One document matched: draft-bryan-p2psip-reload-02.xml
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<front>
<title abbrev="RELOAD">REsource LOcation And Discovery (RELOAD)</title>
<author fullname="Cullen Jennings" initials="C." surname="Jennings">
<organization>Cisco</organization>
<address>
<postal>
<street>170 West Tasman Drive</street>
<street>MS: SJC-21/2</street>
<city>San Jose</city>
<region>CA</region>
<code>95134</code>
<country>USA</country>
</postal>
<phone>+1 408 421-9990</phone>
<email>fluffy@cisco.com</email>
</address>
</author>
<author fullname="Bruce B. Lowekamp" initials="B. B." surname="Lowekamp">
<organization>SIPeerior; William & Mary</organization>
<address>
<postal>
<street>3000 Easter Circle</street>
<city>Williamsburg</city>
<region>VA</region>
<code>23188</code>
<country>USA</country>
</postal>
<phone>+1 757 565 0101</phone>
<email>lowekamp@sipeerior.com</email>
</address>
</author>
<author fullname="Eric Rescorla" initials="E.K." surname="Rescorla">
<organization>Network Resonance</organization>
<address>
<postal>
<street>2064 Edgewood Drive</street>
<city>Palo Alto</city>
<region>CA</region>
<code>94303</code>
<country>USA</country>
</postal>
<phone>+1 650 320-8549</phone>
<email>ekr@networkresonance.com</email>
</address>
</author>
<author fullname="Jonathan Rosenberg" initials="J.D." surname="Rosenberg">
<organization>Cisco</organization>
<address>
<postal>
<street></street>
<city>Edison</city>
<region>NJ</region>
<country>USA</country>
</postal>
<email>jdrosen@cisco.com</email>
</address>
</author>
<date day="18" month="November" year="2007" />
<area>RAI</area>
<workgroup>P2PSIP</workgroup>
<abstract>
<t>This document defines REsource LOcation And Discovery (RELOAD), a
peer-to-peer (P2P) binary signaling protocol for usage on the Internet.
A P2P signaling protocol provides its clients with an abstract hash
table service between a set of cooperating peers that form the overlay
network. RELOAD is designed to support a P2P Session Initiation Protocol
(P2PSIP) network, but it can be utilized by other applications with
similar requirements by defining new usages that specify the data types
that must be stored for a particular application, such as location for
SIP. RELOAD defines a security model based on a certificate enrollment
service that provides unique identities. NAT traversal is a fundamental
service of the protocol.</t>
<t>This draft represents a concrete proposal for the P2PSIP Peer
Protocol. The protocol described here builds on the lessons and
experiences from designing and implementing the dSIP, ASP, and RELOAD
protocols and is a merge of features from RELOAD-01 and ASP.</t>
</abstract>
</front>
<middle>
<section title="Introduction">
<t>This document defines REsource LOcation And Discovery (RELOAD), a
peer-to-peer (P2P) signaling protocol for usage on the Internet. It
provides a Distributed Hash Table (DHT) service, which allows
participating nodes to read and write entries into a hash table that is
stored collectively among the participants. RELOAD is a lightweight,
binary protocol. It provides several functions that are critical for a
successful P2P protocol for the Internet. These are:</t>
<t><list style="hanging">
<t hangText="Security Framework:">Security is one of the most
challenging problems in a P2P protocol. A P2P network will often be
established among a set of peers none of which trust each other.
Yet, despite this lack of trust, the network must operate reliably
to allow storage and retrieval of data. RELOAD defines an abstract
enrollment server, which all entities trust to generate unique
identifiers for each user. Using that small amount of trust as an
anchor, RELOAD defines a security framework that allows for
authorization of P2P protocol functions and authentication of data
stored in the overlay.</t>
<t hangText="Usage Model:">RELOAD is designed to support a variety
of applications, including P2P multimedia communications with the
Session Initiation Protocol <xref
target="I-D.ietf-p2psip-concepts"></xref>. Consequently, RELOAD has
the notion of a usage, one of which is defined to support each
application (this document also defines the SIP usage for multimedia
communications). Each usage identifies a set of data types that need
to be stored and retrieved from the DHT (the SIP usage defines data
types for registrations, certificates, and Traversal Using Relay NAT
(TURN) <xref target="I-D.ietf-behave-turn"></xref> servers). Each
type defines a data structure, authorization policies, size quota,
and information required for storage and retrieval in the DHT. The
usage concept allows RELOAD to be used with new applications through
a simple documentation process that supplies the details for each
application.</t>
<t hangText="NAT Traversal:">Operations for NAT traversal are part
of the base design, including establishing new RELOAD connections
and tunneling SIP or other application protocols required by P2PSIP.
RELOAD makes use of Interactive Connectivity Establishment (ICE)
<xref target="I-D.ietf-mmusic-ice"></xref> to facilitate the
creation of the P2P network and the establishment of links for use
by the application protocol (SIP and RTP, for example). RELOAD also
defines how peers in the P2P network act as STUN and TURN servers
and how those resources can be discovered through the DHT. With
these features, RELOAD can run in modes in which all the peers are
behind NATs, yet are able to fully participate without imposing any
constraints on the actual DHT algorithm or routing topology.</t>
<t hangText="High Performance Routing:">The very nature of DHT
algorithms introduces a requirement that peers participating in the
P2P network route requests on behalf of other peers in the network.
This introduces a load on those other peers, in the form of
bandwidth and processing power. RELOAD has been defined to reduce
the amount of bandwidth and processing required of peers. It does so
by using a very lightweight binary protocol, and furthermore, by
defining a packet structure that facilitates low-complexity
forwarding, including hardware-based forwarding. In particular, a
fixed-length header is used for routing the message through the
overlay without the contents needing to be parsed by (or even
visible to) intermediate peers. The header includes no information
about specific IP addresses because none are needed to route along
an overlay. The header only includes lists of peers which the
message should be routed through/too, as well as some minor options
and version flags. Clearly separating the header components
necessary for routing from the message contents simplifies
processing and increases security.</t>
<t hangText="Transport Flexibility:">RELOAD has native support for
both DTLS and TLS for the underlying transport protocol, with
support for DTLS over UDP as mandatory to implement. TLS over TCP is
preferred because it has better bulk performance and connection
stability, but UDP is more likely to provide direct connections
between peers in the presence of NATs. Explicit support for
fragmentation is provided and required when using UDP. Because there
is no single universally available and suitable transport protocol,
the peer protocol must be flexible in this regard. New transports
can be supported trivially.</t>
<t hangText="Pluggable DHT Algorithms:">RELOAD has been designed
with an abstract interface to the DHT layer to simplify implementing
a variety of DHT algorithms. This specification also defines how
RELOAD is used with Chord, which is mandatory to implement.
Specifying a default "must implement" DHT will allow
interoperability, while the extensibility allows selection of DHTs
optimized for a particular application.</t>
</list></t>
<t>These properties were designed specifically to meet the requirements
for a P2P protocol to support SIP. However, RELOAD is not limited to
usage by SIP and could serve as a tool for supporting other P2P
applications with similar needs. RELOAD is also based on the concepts
introduced in <xref target="I-D.ietf-p2psip-concepts"></xref>.</t>
<section title="Architecture">
<t>Architecturally this specification splits into several layers, as
shown in the following figure.</t>
<figure>
<artwork><![CDATA[
Application
-------------------------------------- Usage-defined API
+-------+ +-------+
Usage | SIP | | XMPP | ...
Layer | Usage | | Usage |
+-------+ +-------+
-------------------------------------- Distributed Storage API
Overlay Overlay +-------------+
Routing & Routing & +----+ | +-----+ |
Storage Replication | DB | | |Chord| ... | Topology
Layer Logic +----+ | | | | Plugins
| +-----+ |
+-------------+
--------------------------------------
+------+ +-----+
Forwarding Forwarding & | STUN | | ICE |
Layer Encoding Logic +------+ +-----+
-------------------------------------- Common Packet Encoding
Transport +-------+ +------+
Layer |TLS | |DTLS |
+-------+ +------+
]]></artwork>
</figure>
<t>The three layers defined by RELOAD include: <list style="hanging">
<t hangText="Usage Layer:">Provides an application-specific
interface that maps an application's requirements onto the generic
services of the DHT.</t>
<t hangText="Overlay Routing & Storage Layer:">Implements the
DHT. Chooses what links to establish to form the DHT's overlay
network, manages the storage and migration of data for this peer
and on behalf of other peers, and performs searches for requested
data across the DHT.</t>
<t hangText="Forwarding Layer:">Provides services analogous to the
Link Layer in the IP model. Also handles setting up connections
across NATs using ICE.</t>
</list></t>
<section title="Usage Layer">
<t>The top layer, called the Usage Layer, has application usages,
such as the SIP Location Usage, that use the abstract distributed
storage API to store and retrieve data from the DHT. The goal of
this layer is to implement application-specific usages of the
Overlay Routing and Storage Layer below it. The Usage defines how a
specific application maps its data into something that can be stored
in the DHT, where to store the data, how to secure the data, and
finally how applications can retrieve and use the data.</t>
<t>The architecture diagram shows both a SIP usage and an XMPP
usage. A single application may require multiple usages. A usage may
define multiple types of data that are stored in the overlay and may
also rely on types originally defined by other usages. A usage is
not itself encoded on the wire --- only the types are --- but is
rather a specification of the functionality that is required for a
given application.</t>
<t>One usage may depend on another. For example, the SIP usage
depends on a Certificate Store usage (not shown in the diagram) to
obtain the certificates required to authenticate messages. Because
certificates are stored in standard X.509 form, there is no reason
for each usage to specify this service independently.</t>
</section>
<section title="Overlay Routing and Storage Layer">
<t>The Overlay Routing and Storage Layer stores and retrieves
information, performs maintenance of the DHT as peers join and leave
the DHT, and routes messages on the overlay. The DHT implementation
is provided by a pluggable component so that each overlay can select
an appropriate DHT that relies on the common RELOAD core code.</t>
<t>The Overlay Routing and Replication Logic provides a fairly
generic interface that allows the DHT implementation to control the
overlay and resource operations and messages. Since each DHT is
defined and functions differently, we generically refer to the table
of other peers that the DHT maintains and uses to route requests
(neighbors) as a Routing Table. The Logic component makes queries to
the DHT's Routing Table to determine the next hop, then encodes and
sends the message itself. Similarly, the DHT issues periodic update
requests through the logic component to maintain and update its
Routing Table.</t>
<t>The DHT shown in the illustration is Chord, but a variety of DHT
algorithms are possible through a pluggable interface. A single node
could be functioning in multiple overlays simultaneously, each using
its own DHT algorithm. Each peer is identified by and its location
in the overlay determined by its Peer-ID that is assigned by the
enrollment server when the user or peer first enrolls in the
overlay. The Peer-ID also determines the range of Resource-IDs for
which it will be responsible. The exact mapping between these is
determined by the DHT algorithm used by the overlay, therefore the
logic component always queries the DHT to determine where a
particular resource should be stored.</t>
<t>As peers enter and leave, resources may be stored on different
peers, so the information related to them is exchanged as peers
enter and leave. Redundancy is used to protect against loss of
information in the event of a peer failure and to protect against
compromised or subversive peers. The Logic component notifies the
DHT as neighbors join and leave, and the DHT updates its Routing
Table and issues resource migration requests as appropriate.</t>
</section>
<section title="Forwarding Layer">
<t>This layer is responsible for getting a packet to the next peer,
as determined by the Routing and Storage Layer. The Forwarding Layer
establishes and maintains the network connections required by the
DHT's Routing Table. This layer is also responsible for setting up
connections to other peers through NATs and firewalls using ICE, and
it can elect to forward traffic using relays for NAT and firewall
traversal.</t>
</section>
</section>
<section title="Security">
<t>RELOAD's security framework is built upon an enrollment server. The
enrollment server issues each new peer a certificate that assigns it a
Peer-ID. By generating the Peer-IDs randomly and controlling what
peers are issued certificates, the enrollment server protects against
many of the attacks on the overlay network. Similarly, all users are
issued certificates for their identities by the enrollment server. All
resources stored on the overlay must be signed by their creator, thus
ensuring that an attacker cannot forge data belonging to another user.
The enrollment process is a one-time-only procedure. The peer or user
do not have to communicate further with it once they have obtained
their certificates.</t>
<t>TLS or DTLS are used for communication between peers. In
combination with the certificates, this provides both confidentiality
and authentication for communication across the overlay. Applications
such as P2PSIP can also make use of the users' certificates to achieve
secure end-to-end connections at the application layer.</t>
<!-- <t>Further security is provided by replicating the resources stored
on the overlay. Even if an attacker can compromise a single peer
(either directly or through the routing), by locating replicas
randomly around the overlay, a valid copy of the data is likely to
be obtained. </t>-->
<t>In addition to the enrollment server model, RELOAD offers a
security model using a pre-shared-key. Although this provides
significantly less security than is provided through an enrollment
server, it allows ad hoc or ephemeral overlays to be set up with
minimal effort on the part of the users.</t>
</section>
</section>
<section title="Terminology">
<t></t>
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in <xref
target="RFC2119">RFC 2119</xref>.</t>
<t>We use the terminology and definitions from the <xref
target="I-D.ietf-p2psip-concepts">Concepts and Terminology for Peer to
Peer SIP</xref> draft extensively in this document. Other terms used in
this document are defined inline when used and are also defined below
for reference.</t>
<t>The following important terms from the Concepts document are defined
below for reference.</t>
<t><list style="hanging">
<t hangText="DHT:" />
<t>A distributed hash table. A DHT is an abstract hash table service
realized by storing the contents of the hash table across a set of
peers.</t>
<t hangText="DHT Algorithm:">An algorithm that defines the rules for
determining which peers in a DHT store a particular piece of data
and for determining a topology of interconnections amongst peers in
order to find a piece of data. Examples of DHT algorithms are Chord,
Bamboo and Tapestry.</t>
<t hangText="DHT Instance:">A specific hash table and the collection
of peers that are collaborating to provide read and write access to
it. There can be any number of DHT instances running in an IP
network at a time, and each operates in isolation of the others.</t>
<t hangText="P2P Network:">Another name for a DHT instance.</t>
<t hangText="P2P Network Name:">A string that identifies a unique
P2P network. P2P network names look like DNS names - for example,
"example.org". Lookup of such a name in DNS would typically return
services associated with the DHT, such as enrollment servers,
bootstrap peers, or gateways (for example, a SIP gateway between a
traditional SIP and a P2P SIP network called "example.com").</t>
<t hangText="Resource-ID:">A non-human-friendly value that
identifies some resources and which is used as a key for storing and
retrieving the resource. One way to generate a Resource-ID is by
applying a mapping function to some other unique name (e.g., User
Name or Service Name) for the resource. The Resource-ID is used by
the distributed database algorithm to determine the peer or peers
that are responsible for storing the data for the overlay.</t>
<t hangText="Peer:">A host that is participating in the DHT. By
virtue of its participation it can store data and is responsible for
some portion of the overlay.</t>
<t hangText="Peer-ID:">A Resource-ID that uniquely identifies a
peer. Peer-IDs 0 and 2^N - 1 are reserved and are invalid peer-IDs.
A value of zero is not used in the wire protocol but can be used to
indicate an invalid peer in implementations and APIs. The peer-id of
2^N-1 is used on the wire protocol as a wildcard.</t>
<t hangText="Resource:">An object associated with an identifier. The
identifier for the object is a string that can be mapped into a
Resource-ID by using the string as a seed to the hash function. A
SIP resource, for example, is identified by its AOR.</t>
<t hangText="User:">A human being.</t>
</list> <t>We also introduce the following important new terms.</t>
<list style="hanging">
<t hangText="Connection Table:">The set of peers to which a peer is
directly connected. This includes peers with which CONNECT
handshakes have been done but which have not sent any UPDATEs.</t>
<t hangText="Routing Table:">The set of peers which a peer can use
to route DHT messages. In general, these peers will all be on the
connection table but not vice versa, because some peers will have
CONNECTed but not sent updates. Peers may send messages directly to
peers which are on the connection table but may only route messages
to other peers through peers which are on the routing table.</t>
<t hangText="Seed:">A seed is a string used as an input to a hash
function, the result of which is a Resource-ID.</t>
<t hangText="Usage:">A usage is an application that wishes to use
the DHT for some purpose. Each application wishing to use the DHT
defines a set of data types that it wishes to use. The SIP usage
defines the location, certificate, STUN server and TURN server data
types.</t>
</list></t>
</section>
<section title="Overview">
<section title="Distributed Storage Layer">
<t>Each logical address in the DHT where data can be stored is
referred to as a Resource-ID. A given peer will be responsible for
storing data from many Resource-ID locations. Typically literature on
DHTs uses the term "key" to refer to a location in the DHT; however,
in this specification the term key is used to refer to public or
private keys used for cryptographic operations and the term
Resource-ID is used to refer to a location for storage in the DHT.</t>
<section title="DHT Concepts">
<t>While very early P2P systems used flood based techniques, most
newer P2P systems locate resources using a Distributed Hash Table,
or DHT to improve efficiency. Peers are organized using a
Distributed Hash Table (DHT) structure. In such a system, every
resource has a Resource-ID, which is obtained by hashing some
keyword or value that uniquely identifies the resource. Resources
can be thought of as being stored in a hash table at the entry
corresponding to their Resource-ID. The peers that make up the
overlay network are also assigned an ID, called a Peer-ID, in the
same hash space as the Resource-IDs. A peer is responsible for
storing all resources that have Resource-IDs near the peer's
Peer-ID. The hash space is divided up so that all of the hash space
is always the responsibility of some particular peer, although as
peers enter and leave the system a particular peer's area may
change. Messages are exchanged between the peers in the DHT as the
peers enter and leave to preserve the structure of the DHT and
exchange stored entries. Various DHT implementations may visualize
the hash space as a grid, circle, or line.</t>
<t>Peers keep information about the location of other peers in the
hash space and typically know about many peers nearby in the hash
space, and progressively fewer more distant peers. We refer to this
table of other peers as a Routing Table. When a peer wishes to
search, it consults the list of peers it is aware of and contacts
the peer with the Peer-ID nearest the desired Resource-ID. If that
peer does not know how to find the resource, it either returns
information about a closer peer it knows about, or forwards the
request to a closer peer. In this fashion, the request eventually
reaches the peer responsible for the resource, which then replies to
the requester.</t>
</section>
<section title="DHT Topology">
<t>Each DHT will have a somewhat different structure, but many of
the concepts are common. The DHT defines a large space of
Resource-IDs, which can be thought of as addresses. In many DHTs,
the Resource-IDs are simply 128- or 160-bit integers. Each DHT also
has a distance metric such that we can say that Resource-ID A is
closer to Resource-ID B than to Resource-ID C. When the Resource-IDs
are n-bit integers, they are often considered to be arranged in a
ring so that (2^n)-1 and (0) are consecutive and distance is simply
distance around the ring.</t>
<t>Each peer in the DHT is assigned a Peer-ID and is "responsible"
for the nearby space of Resource-IDs. So, for instance, if we have a
peer P, then it could also be responsible for storing data
associated with Resource-ID P+epsilon as long as no other peer P was
closer. The DHT Resource-ID space is divided so that some peer is
responsible for each Resource-ID.</t>
</section>
<section anchor="sec.routing" title="Routing">
<t>The way routing works in a DHT is specified by the specific DHT
algorithm but the basic concepts are common to most systems. Each
peer maintains connections to some other set of peers N. There need
not be anything special about the peers in N, except that the peer
has a direct connection to them: it can reach them without going
through any other peer. When it wishes to deliver a message to some
peer P, it selects some member of N, N_i that is closer to P than
itself (as a degenerate case, P may be in N). The peer sends message
to message to N_i. At this point two things can happen:</t>
<t><list style="hanging">
<t hangText="Recursive Routing">N_i repeats the same process as
P, sending the message to one of its peers N_j. This same
process repeats until the message is delivered to N.</t>
<t hangText="Iterative Routing">N_i consults its table of direct
connections and selects a new peer N_j which is closer to N. It
responds to the original sending peer with a redirect to N_j.
The original peer then sends the message to N_j, where the
process repeats until the sending peer is redirected to N.</t>
</list></t>
<t>The advantage of iterative routing is that it consumes less
resources for the intermediate peers; they only have to send
redirect messages rather than forwarding requests and responses. The
advantage of recursive routing is that it does not require the
sending or receiving peer to have a rich set of connections to other
nodes in the overlay. Thus, iterative routing is problematic in
NATed networks because there is no way to guarantee that a peer will
be able to form a connection to whatever peer it is redirected
to.</t>
<t>[[TODO: The details of which routing strategy are to be used and
how they are selected are kind of unclear. This needs WG
discussion.]]</t>
<t>In most DHTs, the peers in N are selected in a particular way.
One common strategy is to have them arranged exponentially further
away from yourself so that any message can be routed in a O(log(N))
steps. The details of the routing structure depend on the DHT
algorithm, however, since it defines the distance metric and the
structure of the connection table.</t>
<t>In RELOAD, messages may either be REQUESTS or RESPONSES to
REQUESTS. Requests are routed as described above. In principle,
responses could be routed the same way. This is called "Asymmetric"
routing because requests and responses will generally follow
different paths through the network. Asymmetric routing makes
diagnosis of errors difficult because you need to be able to acquire
debugging information at multiple locations. In the alternative
strategy, called "Symmetric" routing, as requests travel through the
network they accumulate a history of the peers they passed through
and responses are routed in the opposite direction so that they
follow the same path in reverse. RELOAD supports both flavors of
routing.</t>
<t>Symmetric routing is easier to debug. Symmetric routing is also
required when the overlay topology is changing. For example, when a
new peer is joining the overlay, asymmetric routing cannot work
because the response would not be able to reach the new peer until
it has completed the joining process. Symmetric routing solves this
situation because the response is routed from the admitting peer
through the bootstrap peer, thus relying on a path that is already
known and established. In order to implement symmetric routing,
RELOAD provides the Via List (<xref target="sec-via-list"></xref>)
feature. Asymmetric routing, however, requires no state to be stored
in the message (as a Via List) or in on-path peers.</t>
<t>[[TODO: again, this is a topic that needs WG discussion. It seems
like there are situations where symmetric is very desirable (e.g.,
startup). It's less clear that asymmetric will have a
performance/state difference that will be significant.]]</t>
</section>
<section anchor="sec-typed-data"
title="Storing and Retrieving Typed Data">
<t>The Data Storage Layer provides operations to STORE, FETCH, and
REMOVE data. Each location in the DHT is referenced by a single
integer Resource-ID. However, each location may contain data
elements of multiple types. Furthermore, there may be multiple
values of each type, as shown below.</t>
<figure>
<artwork><![CDATA[
+--------------------------------+
| Resource-ID |
| |
| +------------+ +------------+ |
| | Type 1 | | Type 2 | |
| | | | | |
| | +--------+ | | +--------+ | |
| | | Value | | | | Value | | |
| | +--------+ | | +--------+ | |
| | | | | |
| | +--------+ | | +--------+ | |
| | | Value | | | | Value | | |
| | +--------+ | | +--------+ | |
| | | +------------+ |
| | +--------+ | |
| | | Value | | |
| | +--------+ | |
| +------------+ |
+--------------------------------+
]]></artwork>
</figure>
<t>Each type-id is a code point assigned by IANA. Note that a
type-id may be employed by multiple usages and new usages are
encouraged to use previously defined types where possible. As part
of the type definition, protocol designers may define constraints,
such as limits on size, on the values which may be stored. For many
types, the set may be restricted to a single item; some sets may be
allowed to contain multiple identical items while others may only
have unique items. Some typical types of sets that a type definition
would use include:</t>
<t><list style="hanging">
<t hangText="single value:">There can be at most one item in the
set and any value overwrites the previous item.</t>
<t hangText="array:">Many values can be stored and addressed by
index.</t>
<t hangText="dictionary:">The values stored are indexed by a
key. Often this key is one of the values from the certificate of
the peer sending the STORE request.</t>
</list></t>
<!--
EKR REMOVED
<t>Application usages define the types and any enforceable
constraints. These are implemented by a STORE, FETCH, and REMOVE
methods that are routed to the correct peer by the underling DHT
instance. The STORE and REMOVE requests can affect a single member of
the set or multiple members. The FETCH request returns the complete
set. The security around who can STORE or REMOVE data is defined by
the application's usage, but typically only a specific user can modify
the data at a specific location and the request to modify the data
will be accompanied by a signature that is signed with the appropriate
user's certificate authorizing the request. All data stored in the DHT
has an expiry date after which point it may be discarded.</t>
<t>It is possible to discover whether a specific peer is storing any
records of a particular type using the FIND operation. This operation only
looks on a single peer and does not require the underlying DHT
implementation to provide search functionality. The FIND request
also returns various statistics about the peer that is storing the
data. These statistics include the portion of the Resource-ID space the
peer is responsible for and the number of items it is storing. These
can be used to estimate the number of unique Resource-ID and peers in the
DHT.</t>
-->
</section>
<section anchor="sec-join-leave-maint"
title="Joining, Leaving, and Maintenance">
<t>When a new peer wishes to join the DHT, it must have a peer-id
that it is allowed to use. It uses one of the peer-ids in the
certificate it received from the enrollment server. The main steps
in joining the DHT are:</t>
<t><list style="symbols">
<t>Forming connections to some other peers.</t>
<t>Acquiring the data values this peer is responsible for
storing.</t>
<t>Informing the other peers which were previously responsible
for that data that this peer has taken over responsibility.</t>
</list></t>
<t>First, the peer ("JP," for Joining Peer) uses the bootstrap
procedures to find some (any) peer in the DHT. It then typically
contacts the peer which would have formerly been responsible for the
peer's Resource-ID (since that is where in the DHT the peer will be
joining), the Admitting Peer (AP). It copies the other peer's state,
including the data values it is now responsible for and the
identities of the peers with which the other peer has direct
connections.</t>
<t>The details of this operation depend mostly on the DHT involved,
but a typical case would be:</t>
<t><list style="numbers">
<t>JP sends a JOIN request to AP announcing its intention to
join.</t>
<t>AP sends an OK response.</t>
<t>AP does a sequence of STOREs to JP to give it the data it
will need.</t>
<t>AP does UPDATEs to JP and to other peers to tell it about its
own routing table. At this point, both JP and AP consider JP
responsible for some section of the DHT.</t>
<t>JP makes its own connections to the appropriate peers in the
DHT.</t>
</list></t>
<t>After this process is completed, JP is a full member of the DHT
and can process STORE/FETCH requests.</t>
</section>
</section>
<section title="Forwarding Layer">
<t>The forwarding layer is responsible for looking at message and
doing one of three things: <list style="symbols">
<t>Deciding the message was destined for this peer and passing the
message up to the layer above this.</t>
<t>Looking at the peer-id that represents the next peer to send
the message too and if there is an existing connection, sending
the message over the connection.</t>
<t>Requesting the DHT Routing logic to tell the forwarding layer
which peer the message needs to be forwarded to, and then sending
the message.</t>
</list></t>
<section anchor="direct.connect" title="Forming Direct Connections">
<t>As described in <xref target="sec.routing"></xref>, a peer
maintains a set of direct connections to other peers in the DHT.
Consider the case of a peer JP just joining the DHT. It communicates
with the admitting peer AP and gets the list of the peers in AP's
routing table. Naively, it could simply connect to the IP address
listed for each peer, but this works poorly if some of those peers
are behind a NAT or firewall. Instead, we use the CONNECT request to
establish a connection.</t>
<t>Say that peer A wishes to form a direct connection to peer B. It
gathers ICE candidates and packages them up in a CONNECT request
which it sends to B through usual DHT routing procedures. B does its
own candidate gathering and sends back an OK response with its
candidates. A and B then do ICE connectivity checks on the candidate
pairs. The result is a connection between A and B. At this point, A
and B can add each other to their routing tables and send messages
directly between themselves without going through other DHT
peers.</t>
<t>In general, a peer needs to maintain connections to all of the
peers near it in the DHT and to enough other peers to have efficient
routing (the details depend on the specific DHT). If a peer cannot
form a connection to some other peer, this isn't necessarily a
disaster; DHTs can route correctly even with not fully connected
links. However, a peer should try to maintain the specified link set
and if it detects that it has fewer direct connections, should form
more as required.</t>
</section>
<section anchor="sec-via-list" title="Via Lists">
<t>In a general messaging system, messages need a source and a
destination and peers need to be able to send a response to the peer
that sent the request. This can be particularly tricky in overlay
networks when a new peer is joining, or the overlay network is
stabilizing and different peers have different ideas on what the
overlay topology is. A simple and reliable way to make sure that a
response can reach the node that sent the request in these
situations is to have the response traverse the reverse path of the
request.</t>
<t>The approach used to do this is to have each node the request
traverses add its peer-id to the "via list" in the request. Then the
response is routed by looking at the list and using it as list of
peers that the response will be routed thorough. To support this,
each message has a route list of nodes it needs to be routed through
as well as a via list of what nodes it has traversed.</t>
<t>When a peer receives a message from the Transport Layer, it adds
the peer-id of the node it received the message from to the end of
the via list. When a peer goes to transmit a message to the
Transport Layer, it looks at the first entry on the route list. If
the entry is this peer, it removes this entry from the list and
looks at the next entry and if the entry is not this peer, it sends
the message to the first peer on the route list.</t>
<t>When a peer goes to send a response to a request, it can simply
copy the via list in reverse to form the route list for the response
if it wishes to route the response along the reverse path as the
request. [Discussion is need about if all responses are routed this
way or not]</t>
<t>Peers that are willing to maintain state may do list compression
for privacy reason and to reduce the message size. They do this by
taking some number of entries off the via list and replacing them
with a unique entry that this peer can later identify. Later, if the
peer sees the unique entry in a route list, it removes the unique
entry and replaces it with the all the entries removed from the
original via list (and reverses the order of these entries). Note
that this technique will generally require storing some per-message
state on the intermediate peer, so this is a bandwidth/per-peer
state tradeoff. The exception is if the list is not compressed but
rather the peer-ids are simply encrypted.</t>
<t>The via list approach provides several features. First it allows
a response to follow the same path as the request. This is
particularly important for peers that are sending requests while
they are joining and before other peers can route to them as well as
situations where message are being exchanged to stabilize the
overlay network. It also makes it easier to diagnose and manage the
system when all peers see the response to any request they
forward.</t>
</section>
<section title="Clients">
<t>RELOAD also allows for the possibility of Client nodes. A client
is a node which connects to an admitting peer (or peers) like an
ordinary peer but never sends a JOIN or an UPDATE. It is therefore
in the AP's connection table but not routing table and never is used
to store any DHT data. However, because it is reachable through the
AP, it can still send and receive messages. The client MUST still
have the usual credentials.</t>
<t>Because the client may only have a connection to a single AP,
which, due to topology shifts may no longer be the responsible peer,
clients SHOULD use symmetric routing and should advertise route
lists that contain both the AP to which they are connected and
themselves. E.g., if the client has peer-id X and the AP has peer-id
Y, the client should advertise the route list (Y, X). This
guarantees reachability.</t>
<t>Note that clients MAY also contact APs which are not in fact
responsible for the client's peer-id.</t>
</section>
</section>
<section title="Transport Layer">
<t>This layer sends and receives messages over TLS and DTLS. For TLS
it simply pushes the messages into the stream. For DTLS it takes care
of fragmentation issues. The reason for including TLS is the improved
performance it can offer for bulk transport of data. The reason for
including DTLS is that the percentage of the time that two devices
behind NATs can form a direct connection without a relay is much
higher for DTLS than for TLS.</t>
</section>
<section title="Enrollment">
<t>Before a new user can join the DHT for the first time, they must
enroll in the P2P Network for the DHT they want to join. Enrollment
will typically be done by contacting a centralized enrollment server.
Other approaches (for instance static out of band configuration) are
possible but are outside the scope of this specification. During
enrollment a new node learns about a particular overlay, sets up a
names and credentials, and discovers the bootstrap nodes. This would
typically be done when a new peer joined an overlay for the very first
time. Bootstrap is the process that happens each time a node boots and
is how the peer finds an node that can be used to join the
overlay.</t>
<t>Before a node can join an overlay, it needs to be provided with a
name for the overlay. Some examples are "example.com", "example", and
"example.local". An DNS SRV lookup is done on this name for the
service name p2p_enroll and a proto of tcp. If the TLD for the name is
.local, then this DNS SRV lookup is done using <xref
target="I-D.cheshire-dnsext-multicastdns"></xref> and the service name
p2p_menroll. The intention here is to support ad hoc/local overlays.
The resulting DNS lookup will provide the address of a enrollment
server. Once this server is found, HTTPS is used to retrieve a XML
file that contains the parameters for the overlay. These include
things such as: what algorithms the overlay uses, overlay parameters,
what usages are a peer on this overlay is required to support, the
type of credentials required, addresses of credentials servers, the
root certificate for the DHT, information about the DHT algorithm that
is being used, a P2P-Network-Id that uniquely identifies this ring,
and any other parameters it may need to connect to the DHT. The DHT
also informs the peers what Usages it is required to support to be a
peer on this P2P Network. An initial list of bootstrap nodes that
consist of multiple bootstrap entries that each have the IP address
and port for contacting a bootstrap server. Some of the address may be
multicast addresses. In the case of multicast DNS, every peer may also
act as an enrollment server.</t>
<t>If shared-key security (<xref target="sec-shared-key"></xref>) is
being used, then the peer can proceed directly to bootstrap. If
certificate-based security (<xref target="sec-cert-security"></xref>
is being used, the peer MUST contact the credential server to obtain a
certificate.</t>
<section title="Certificate Issuance">
<t>Once the peer has the XML file that identifies if credentials are
needed, it can contact the credential server. The user establishes
his identity to the server's satisfaction and provides the server
with its public key. The centralized server then returns a
certificate binding the user's user name to their public key. The
properties of the certificate are discussed more in <xref
target="sec-security-intro"></xref>. The amount of authentication
performed here can vary radically depending on the DHT network being
joined. Some networks may do no verification at all and some may
require extensive identity verification. The only invariant that the
enrollment server needs to ensure is that no two users may have the
same identity.</t>
</section>
<section title="Bootstrap">
<t>The above steps are only done the first time a peer joins a new
overlay or when the overlay parameters are close to expiring and
need to be refreshed. The next step is the bootstrap step which is
done every time the peer boots.</t>
<t>Bootstrapping consists of looking at the list of cached nodes and
bootstraps nodes and sending a RELOAD PING to them to see if they
respond. Once a node responds, it can be used to join the overlay.
After a node has joined, it keeps track of a small number of peers
to which it could directly connect. Theses are saved as the cached
nodes and used next time the peer boots. The point of the cached
nodes is to reduce the load on the bootstrap nodes.</t>
</section>
</section>
<section anchor="sec-security-intro" title="Security">
<section anchor="sec-cert-security" title="Certificate-Based Security">
<t>The certificate-based security model revolves around the
enrollment process allocating a unique name to the user and issuing
a certificate <xref target="RFC3280"></xref> for a public/private
key pair for the user. All peers in a particular DHT can verify
these certificates. A given peer acts on behalf of a user, and that
user is somewhat responsible for its operation.</t>
<t>The certificate serves two purposes:</t>
<t><list style="symbols">
<t>It entitles the user to store data at specific locations in
the DHT.</t>
<t>It entitles the user to operate a peer that has a peer-id
found in the certificate. When the peer is acting as a DTLS or
TLS server, it can use this certificate so that a client
connecting to it knows it is connected to the correct
server.</t>
</list></t>
<t>When a user enrolls, or enrolls a new device, the user is given a
certificate. This certificate contains information that identifies
the user and the device they are using. If a user has more than one
device, typically they would get one certificate for each device.
This allows each device to act as a separate peer.</t>
<t>The contents of the certificate include:</t>
<t><list style="symbols">
<t>A public key provided by the user.</t>
<t>Zero, one, or more user names that the DHT is allowing this
user to use. For example, "alice@example.org". Typically a
certificate will have one name. In the SIP usage, this name
corresponds to the AOR.</t>
<t>Zero, one, or more peer-ids. Typically there will be one
peer-id. Each device will use a different peer-id, even if two
devices belong to the same user. Peer-IDs should be chosen
randomly by the enrollment server.</t>
<t>A serial number that is unique to this certificate across all
the certificates issued for this DHT.</t>
<t>An expiration time for the certificate.</t>
</list></t>
<t>Note that because peer-IDs are chosen randomly, they will be
randomly distributed with respect to the user name. This has the
result that any given peer is highly unlikely to be responsible for
storing data corresponding to its own user, which promotes high
availability.</t>
<section title="Storage Permissions">
<t>When a peer uses a STORE request to place data at a particular
location X, it must sign with the private key that corresponds to
a certificate that is suitable for storing at location X. Each
data type in a usage defines the exact rules for determining what
certificate is appropriate. However, the most natural rule is that
a certificate for a user name or peer-id X is a permission to
store data at the same resource id that would be found by an
attempt to look up X.</t>
<t>The digital signature over the data serves two purposes. First,
it allows the peer responsible for storing the data to verify that
this STORE is authorized. Second, it provides integrity for the
data. The signature is saved along with the data value (or values)
so that any reader can verify the integrity of the data. Of
course, the responsible peer can "lose" the value but it cannot
undetectably modify it.</t>
</section>
<section title="Peer Permissions">
<t>The second purpose of a certificate is to allow the device to
act as a peer with the specified peer-ID. When a peer wishes to
connect to peer X, it forms a TLS/DTLS connection to the peer and
then performs TLS mutual authentication and verifies that the
presented certificate contains peer-ID X.</t>
<t>Note that because the formation of a connection between two
nodes generally requires traversing other nodes in the DHT, as
specified in <xref target="direct.connect"></xref>, those nodes
can interfere with connection initiation. However, if they attempt
to impersonate the target peer they will be unable to complete the
TLS mutual authentication: therefore such attacks can be
detected.</t>
</section>
<section title="Expiry and Renewal">
<t>At some point before the certificate expires, the user will
need to get a new certificate from the enrollment server.</t>
</section>
</section>
<section anchor="sec-shared-key" title="Shared-Key Security">
<t>RELOAD also defines a shared-key security model which can be used
in closed networks where the peers are not mutually suspicious. In
this model, the peers all share a single key which is used to
authenticate the peer-to-peer DTLS connections via TLS-PSK. If
shared-key security mode is in use, a TLS-PSK cipher suite MUST be
used. This is useful for admission control, but is completely unsafe
in any setting where peers are not mutually trusted, since it allows
any peer to impersonate any other peer.</t>
</section>
</section>
<section title="Migration">
<t>At some point in time, a given P2P Network may want to migrate from
one underlying DHT algorithm to another or update to a later extension
of the protocol. This can also be used for crypto agility issues. The
migration approach is done by basically having peers initializing
algorithm A. When the clients go to periodically renew their
credentials, they find out that the P2P Network now requires them to
use algorithm A but also to store all the data with algorithm B. At
this point there are effectively two DHT rings in use, rings A and B.
All data is written to both but queries only go to A. At some point
when the clients periodically renew their credentials, they learn that
the P2P Network has moved to storing to both A and B but that FETCH
requests are done with P2P Network B and that any SEND should first be
attempted on P2P Network B and if that fails, retried on P2P Network
A. In the final stage when clients renew credentials, they find out
that P2P Network A is no longer required and only P2P Network B is in
use. Some types of usages and environments may be able to migrate very
quickly and do all of these steps in under a week, depending on how
quickly software that supports both A and B is deployed and how often
credentials are renewed. On the other hand, some very ad-hoc
environments involving software from many different providers may take
years to migrate.</t>
</section>
<section title="Usages Layer">
<t>By itself, the distributed storage layer just provides
infrastructure on which applications are built. In order to do
anything useful, a usage must be defined. Each Usage needs to specify
several things:</t>
<t><list style="symbols">
<t>Register code points for any type that the Usage defines.</t>
<t>Define the data structure for each of the types.</t>
<t>Define access control rules for each type.</t>
<t>Provide a size limit for each type.</t>
<t>Define how the seed is formed that is hashed to form the
Resource-ID where each type is stored.</t>
<t>Describe how values will be merged after a network partition.
Unless otherwise specified, the default merging rule is to act as
if all the values that need to be merged were stored and that the
order they were stored in corresponds to the storing times
associated with (and carried in) their values.</t>
</list></t>
<t>The types defined by a usage may also be applied to other usages.
However, a need for different parameters, such as different size
limits, would imply the need to create a new type.</t>
<section anchor="sec-sip-usage" title="SIP Usage">
<t>From the perspective of P2PSIP, the most important usage is the
SIP Usage. The basic function of the SIP usage is to allow Alice to
start with a SIP URI (e.g., "bob@dht.example.com") and end up with a
connection which Bob's SIP UA can use to pass SIP messages back and
forth to Alice's SIP UA.</t>
<!--
<t>This operation can take a number of forms, but in the simplest
case, Bob's SIP UA has peer-ID "B". When Bob joins the DHT (i.e.,
turns on his phone), he stores the following mapping in the DHT:</t>
<t><list style="symbols">
<t>sip:bob@dht.example.com -> B</t>
</list></t>
<t>When Alice wants to call Bob, she starts with his URI and her UA
uses the DHT to look up his peer-ID B. She then routes a message
through the DHT to B requesting a direct connection. Once this
connection is established she can send SIP messages over it, which
allows her to set up the phone call.</t>
-->
<t>This is done using three key operations that are provided by the
SIP Usage. They are:</t>
<t><list style="symbols">
<t>Mapping SIP URIs that are not GRUUs to other SIP URIs or to
the DHT peer responsible for the SIP UA.</t>
<t>Mapping SIP GRUUs to the DHT peer responsible for the SIP
UA.</t>
<t>Forming a connection directly to a DHT peer that is used to
send SIP messages to the SIP UA.</t>
</list></t>
<t>All SIP URIs for a given overlay MUST be constructed so that they
terminate in the domain name of the overlay. For instance, if the
overlay name is "example.com", then all AORs must be of the form
{sip,sips}:username@example.com. Accordingly, to dereference a URI,
a P2PSIP implementation MUST check to see if the domain matches an
overlay which it is a member of. If so, it uses the following
procedures. Otherwise, it MUST follow <xref target="RFC3263"></xref>
procedures. Note that unless the P2PSIP overlay provides some kind
of SIP gateway, this is likely to be only partially successful,
since, for instance, the callee may not be able to call back.</t>
<section title="SIP Location">
<t>A peer acting as a SIP UA stores their registration information
in the DHT by storing either another URI (for retargeting) or a
route lists to reach them at a Resource-ID in the DHT formed from
the user's SIP AOR. When another peer wishes to find a peer that
is registered for a SIP URI, the lookup of the user's name is done
by taking the user's SIP Address or Record (AOR) and using it as
the seed that is hashed to get a Resource-ID. When the seed is
dereferenced, the result is a set of values. Each value is either
another SIP URI or a route list. If the value is a SIP URI, the
calling peer looks up that URI and continues the process until he
gets a route list.</t>
<t>If the value is a route list, then it is used to reach a peer
that represents a SIP UA registered for that AOR. Typically this
route list will have just one entry but in the case of peers or
clients that can not be directly reached, a route list with more
than one entry may need to be used.</t>
<t>The seed for this usage is a user's SIP AOR, such as
"sip:alice@example.com". This allows the set to store many values
but only one for each peer. The authorization policy is that STORE
requests are only allowed if the user name in the signing
certificate, when turned into a SIP URL and hashed, matches the
Resource-ID. This policy ensures that only a user with the
certificate with the user name "alice@example.com" can write to
the Resource-ID that will be used to look up calls to
"sip:alice@example.com".</t>
<t>Open Issue: Should the seed be "sip:alice@example.com",
"alice@example.com", or a string that includes the code point
defined for the type? The issue here is determining whether
different usages that store data at a seed that is primarily
formed from "alice@example.com" should hash to the same
Resource-ID as the SIP Usage. For example, if a buddy list had a
seed that was roughly the same, would we want the buddy list
information to end up on the same peers that stored the SIP
location data or on different peers?</t>
</section>
<section title="SIP GRUUs">
<t>GRUUs that refer to peers in the P2P network are constructed by
simply forming a GRUU, where the value of gr URI parameter
contains a base64 encoded version of the route list that will
reach the peer. Typically the route list is just a single entry
with the peer-id of peer.</t>
</section>
<section title="SIP Connect">
<t>This usage allows two clients to form a new TLS or DTLS
connection between them and then use this connection for sending
SIP messages to one another. This does not store any information
in the DHT, but it allows the CONNECT request to be used to set up
a TLS or DTLS connection between two peers and then use that
connection to send SIP messages back and forth.</t>
<t>The CONNECT request will ensure that the connection is formed
to a peer that has a certificate which includes the user that the
connection is being formed to.</t>
</section>
<section title="SIP Tunnel">
<!-- EKRTODO: remove?-->
<t>This TUNNEL request allows two peers to exchange SIP messages
across the overlay using the TUNNEL method without first setting
up a direct connection using CONNECT. This allows a SIP message to
be sent immediately, without the delay associated with CONNECT and
for a simple SIP exchange, it may result in fewer messages being
sent.</t>
</section>
</section>
<section title="Certificate Store Usage">
<t>This usage allows each user to store their certificate in the DHT
so that it can be retrieved to be checked by various peers and
applications. Peers acting on behalf of a particular user store that
user's certificate in the DHT, and any peer that needs the
certificate can do a FETCH to retrieve the certificate. Typically it
is retrieved to check a signature on a request or the signature on a
chunk of data that the DHT has received.</t>
</section>
<section title="TURN Usage">
<t>This usage defines a new type for finding STUN-Relay servers. Any
peer that supports this usage saves a pointer to the IP address and
port of the TURN server in the DHT. When a peer wishes to discover a
TURN server, it picks a random Resource-ID and performs a FIND at
that Resource-ID for the appropriate type for the service. If
nothing is found, this can be repeated until an appropriate set of
servers are found.</t>
</section>
<section title="Other Usages">
<t>This will likely be left out of scope of the initial system but
just to give people a flavor of how these issues might be dealt
with....</t>
<section title="Storing Buddy Lists">
<t>Buddy lists with reciprocal subscribes - when see indication
buddy might be online, such as SUBSCRIBE from buddy, retry
SUBSCRIBE to buddy. Subscriber ends up doing composition.</t>
<t>Single users with different devices can synchronize buddy lists
when both are online</t>
</section>
<section title="Storing Users' VCards"></section>
<section title="Finding Voicemail Message Recorder">
<t>Voicemail is a complicated problem because the amount of
storage required to store a voicemail message can be large. Some
proposed designs may require peers to store voicemail and others
may require users to provide their own storage and delivery
systems. Accordingly, this is being left out of the base
protocol.</t>
</section>
<!-- <section title="ID/Locator Mappings"></section> -->
</section>
</section>
<figure>
<!-- begin-prologue -->
<artwork><![CDATA[
primitive uint8 8;
primitive uint16 16;
primitive uint24 24;
primitive uint32 32;
primitive int32 32;
primitive uint64 64;
primitive uint128 128;
primitive char 8;
primitive opaque 8;
primitive blob 0;
typedef char string<65000>;
primitive peer_id 128;
primitive resource_id 128;
typedef uint32 overlay;
typedef uint64 transaction_id;
typedef uint24 type_id;
typedef uint64 generation_counter;
struct {
uint32 addr;
uint16 port;
} ip4_addr_port;
struct {
uint128 addr;
uint16 port;
} ip6_addr_port;
enum {ip4_address_type (1), ip6_address_type (2)} address_type;
select {
case ip4_address_type:
ip4_addr_port v4;
case ip6_address_type:
ip6_addr_port v6;
} ip_address_and_port;
]]></artwork>
<!-- end-prologue -->
</figure>
</section>
<section anchor="sec-base-protocol" title="Base Protocol">
<t>RELOAD is a message-oriented request/response protocol. The messages
are encoded using binary fields. All integers are represented in network
byte order. The general philosophy behind the design was to use Type,
Length, Value fields to allow for extensibility. However, for the parts
of a structure that were required in all messages, just define theses in
a fixed position as adding a type and length for them is unnecessary and
would simply increases bandwidth and introduces new potentials for
interoperability issues.</t>
<t>Each message has three parts:</t>
<t><list style="hanging">
<t hangText="Forwarding Header:">Each message has a generic header
which is used to forward the message between peers and to its final
destination. This header is the only information that an
intermediate peer (i.e., one that is not the target of a message)
needs to examine.</t>
<t hangText="Message Contents:">The message being delivered between
the peers. From the perspective of the forwarding layer, the
contents is opaque, however, it is interpreted by the higher
layers.</t>
<t hangText="Signature:">A digital signature over the message
contents and parts of the header of the message. Note that this
signature can be computed without parsing the message contents.</t>
</list></t>
<t>The following sections describe the format of each part of the
message.</t>
<section anchor="sec-forwarding-header" title="Forwarding Header">
<t>The layout of the forwarding header is shown below</t>
<t><artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| R | E | L | O |
4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Overlay |
8 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |F|L| |
| TTL | Routing |R|F| Fragment Offset |
| | |A|R| |
| | |G|G| |
12 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|E| | |
|X| Version | Length |
|P| | |
16 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transaction ID |
+ +
| |
24 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Route | Via | |
| List | List | Flags |
| Length | Length | |
28 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Route List //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Via List //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Route Log //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork></t>
<t>The first four bytes identify this message as a RELOAD message.</t>
<t>The Overlay field is the 32bit checksum/hash of the overlay being
used. The CRC-32 checksum MUST be used to convert the variable length
string representing the overlay name into a 32bit value. The purpose
of this field is to allow nodes to participate in multiple overlays
and to detect accidental misconfiguration.</t>
<t>TTL (time-to-live) is an 8 bit field indicating the number of
iterations, or hops, a message can experience before it is discarded.
The TTL u_int8 number MUST be stored in network byte order and MUST be
decremented by one at every hop along the route the message traverses.
If the TTL is 0, the message MUST NOT be propagated further and MUST
be discarded. The initial value of the TTL should be TBD.</t>
<t>Routing is an 8 bit field that specifies the type of routing the
requester would like for the message. The following Routing options
MUST be understood:</t>
<t><list style="empty">
<artwork><![CDATA[
UNSPECIFIED : 0x00
RECURSIVE : 0x01
ITERATIVE : 0x02
]]></artwork>
</list></t>
<t>If a peer is unable or unwilling to perform the type of routing
requested, the peer MUST respond with a 499 error message that
indicates its unwillingness to process the message.</t>
<!--
<t>[[Open Issue: It is possible to indicate what type of routing
using the TTL field. If TTL is 0, assume iterative, otherwise
assume recursive. Do we want to do this?]] </t>
-->
<t>FRAG is a 1 bit field used to specify if this message is a
fragment.</t>
<t><list style="empty">
<artwork><![CDATA[
NOT-FRAGMENT : 0x0
FRAGMENT : 0x1
]]></artwork>
</list></t>
<t>LFRG is a 1 bit field used to specify whether this is the last
fragment in a complete message.</t>
<t><list style="empty">
<artwork><![CDATA[
NOT-LAST-FRAGMENT : 0x0
LAST-FRAGMENT : 0x1
]]></artwork>
</list></t>
<t>[[Open Issue: How should the fragment offset and total length be
encoded in the header? Right now we have 14 bits reserved with the
intention that they be used for fragmenting, though additional bytes
in the header might be needed for fragmentation.]]</t>
<t>EXP is a 1 bit field that specifies if this protocol is
experimental or not. The EXP bit can be set to denote that this
version of the protocol is private, in-house. This makes it possible
to have private protocol versions that don't collide with IETF
standards.</t>
<t>Version is a 7 bit field that indicates the version of the RELOAD
protocol being used.</t>
<t><list style="empty">
<artwork><![CDATA[
Version1.0 : 0x1
]]></artwork>
</list></t>
<t>The message Length is the count in bytes of the size of the
message, including the header.</t>
<t>The Transaction ID is a unique 64 bit number that identifies this
transaction and also serves as a salt to randomize the request and the
response. Responses use the same Transaction ID as the request they
correspond to. Transaction IDs are also used for fragment
reassembly.</t>
<t>The Route List Length and the Via List Length contain the lengths
of the route and via lists respectively, in the number of
peer-ids.</t>
<t>[[Open Issue: How should we handle peer-id lengths? This basically
assumes they're fixed length per DHT algorithm (but not fixed-length
for RELOAD) so that you can unambiguously parse things. Should we have
a length byte?]]</t>
<t>The flags word contains control flags. There is one currently
defined flag.</t>
<t><list style="empty">
<artwork><![CDATA[
ROUTE-LOG : 0x1
]]></artwork>
</list></t>
<t>The ROUTE-LOG flag indicates that the route log should be included
(see <xref target="sec-route-log"></xref></t>
<t>The Route List contains a sequence of peer-ids which the message
should pass through. The route list is constructed by the message
originator. The route list shrinks as the message traverses each
listed peer.</t>
<t>The Via List contains the sequence of peer-ids through which the
message has passed. The via list starts out empty and grows as the
message traverses each peer.</t>
<section anchor="sec-reload-diffs"
title="Changes to Forwarding Header">
<t>The RELOAD-01 forwarding header was completely fixed, whereas
this header includes lists that change en-route. However, this type
of operation is easily accomplished in both software and hardware,
therefore we still view it as a low-overhead header. The changes
include the following.</t>
<list style="symbols">
<t>Rearranged fields to have a cleaner separation between payload
and header.</t>
<t>Removed DHT, Hash, and Security parameters. These are now in
the overlay bootstrap system rather than per-message.</t>
<t>Source and destination IDs are now route lists to accommodate
source routing and recursion without state on intermediate
peers.</t>
<t>Added route log to header to allow payload/header
separation.</t>
</list>
</section>
<section anchor="sec-transport-routing" title="Message Routing">
<section anchor="sec-request-origination"
title="Request Origination">
<t>In order to send a message to a given peer-id or resource-id, a
peer must construct an appropriate route list. The most common
such route list is a single entry containing the peer/resource-id.
This simply uses the normal DHT routing mechanisms to forward the
message to that destination.</t>
<t>Messages can also be source routed. In order to construct a
source route, the originator provides a route list containing a
sequence of resource-ids. The semantics of this route list are
that the message is to traverse in order (potentially with
intermediate hops) each entry on the route list. As each peer is
traversed, that entry is removed from the route list. This makes
it possible to address a peer which is potentially behind a NAT or
a firewall in such a way that it cannot be connected to directly
under any circumstances.</t>
</section>
<section anchor="sec-response-origination"
title="Response Origination">
<t>When a peer sends a response to a request, it SHOULD construct
the route list by reversing the order of the entries on the via
list. This has the result that the response traverses (at least)
the same peers as the request traversed, except in reverse order
(symmetric routing). For asymmetric routing, the peer MAY simply
use the first entry on the via list.</t>
</section>
<section anchor="sec-message-forwarding"
title="Message Receipt and Forwarding">
<t>When a peer receives a message, it first examines the overlay,
version, and other header fields to determine whether the message
is one it can process. If any of these are incorrect (e.g., the
message is for an overlay in which the peer does not participate)
it is an error. The peer SHOULD generate an appropriate error but
MAY simply drop the message.</t>
<t>Once the peer has determined that the message is correctly
formatted, it examines the first entry on the route list. There
are three possible cases here:</t>
<t><list style="symbols">
<t>The first entry on the route list is a private id which is
being used for route list compression.</t>
<t>The first entry on the route list is an id for which the
peer is responsible.</t>
<t>The first entry on the route list is for which another peer
is responsible.</t>
</list></t>
<t>These cases are handled separately.</t>
<section anchor="sec-private-peer-id" title="Private ID">
<t>If the first entry on the route list is a private id, the
peer replaces that entry with the store local value that it
indexes and then re-examines the route list to determine which
case now applies.</t>
</section>
<section anchor="sec-responsible-id" title="Responsible ID">
<t>If the first entry on the route list is a id for which the
peer is responsible, the peer strips the entry off the route
list. If there are remaining entries on the route list, the peer
then re-examines the route list to determine which case now
applies. If the route list is now empty, then the message was
destined for this peer and it MUST pass it to the next layer
up.</t>
</section>
<section anchor="sec-other-id" title="Other ID">
<t>If neither of the other two cases applies, then the peer MUST
forward the message towards the first entry on the route list.
This means that it MUST select one of the peers in its route
table which is closer to the first entry than to itself and send
the message to that peer. If the first entry on the route list
is in the peer's connection table, then it SHOULD forward the
message to that peer directly.</t>
<t>When forwarding a message, the peer MUST:</t>
<t><list style="symbols">
<t>Decrement the TTL value</t>
<t>Update the via list.</t>
</list></t>
<t>The natural way to update the via list is simply to add the
peer-id of the peer from which the message was received to the
end of the list. However, peers may use any algorithm of their
choice provided that if the peer received a route list
constructed by reversing the via list it would be able to route
the outgoing message correctly, enabling symmetric routing.</t>
<t>For instance, if node D receives a message from node C with
via list (A, B), the simple approach is simply to forward to the
next node (E) with via list (A, B, C). Now, if E wants to
respond to the message, it reverses the via list to produce the
route list, resulting in (D, C, B, A). When D forwards the
response to C, the route list will contain (B, A). However, node
D could also list compression and send E the via list (X). E
would then use the route list (D, X). When D processes this
route list, it MUST detect that X is a compressed entry, recover
the via list (A, B, C), and reverse that to produce the correct
route list (C, B, A) before sending it to C.</t>
<t>Note that if a peer is using list compression and then exits
the overlay, the message cannot be forwarded and will be
dropped. The ordinary timeout and retransmission networks
provide stability over this type of failure.</t>
</section>
</section>
</section>
<section anchor="sec-frag-reass" title="Fragmentation and Reassembly">
<t>In order to allow transport over datagram protocols, RELOAD
messages may be fragmented. If a message is too large for a peer to
transmit to the next peer it MUST fragment the message. Note that
this implies that intermediate peers may re-fragment messages if the
incoming and outgoing paths have different maximum datagram sizes.
Intermediate peers SHOULD NOT reassemble fragments.</t>
<t>Upon receipt of a fragmented message by the intended peer, the
peer holds the fragments in a holding buffer until the entire
message has been received. The message is then reassembled into a
single unfragmented message and processed. In order to prevent
denial of service attacks, receivers SHOULD time out incomplete
fragments. [[TODO: Describe algorithm]]</t>
</section>
<section anchor="sec-route-log" title="Route Logging">
<t>The route logging feature provides diagnostic information about
the path taken by the request so far and in this manner it is
similar in function to <xref target="RFC3261">SIP's</xref> Via
header field. If the ROUTE-LOG flag is set in the Flags word, at
each hop peers MUST append a route log entry to the route log
element in the header. The order of the route log entry elements in
the message is determined by the order of the peers were traversed
along the path. The first route log entry corresponds to the peer at
the first hop along the path, and each subsequent entry corresponds
to the peer at the next hop along the path. If the ROUTE-LOG flag is
set in a request, the route log MUST be copied into the response and
the ROUTE-LOG flag set so that the originator receives the ROUTE-LOG
data.</t>
<figure>
<!-- begin-pdu-->
<artwork><![CDATA[
public struct {
route_log_entry entries<65000>;
} route_log;
]]></artwork>
</figure>
<t>The route log is simply a variable length list of route log
entries. The first two bytes are the length, followed by a sequence
of route leg entries, each of which may be individually parsed.</t>
<figure>
<!-- begin-pdu-->
<artwork><![CDATA[
struct {
peer_id id;
uint32 uptime;
opaque certificate<65000>;
ip_address_and_port address;
} peer_info_data;
public struct {
string version;
uint8 transport;
peer_info_data peer_info;
} route_log_entry;
]]></artwork>
</figure>
<t>Each route log entry consists of the following values:</t>
<list style="hanging">
<t hangText="Version -">A textual representation of the software
version</t>
<t hangText="Transport -">The transport type, 1 for TLS, 2 for
DTLS</t>
<t hangText="Id -">The peer-id of the peer.</t>
<t hangText="Uptime -">The uptime of the peer in seconds.</t>
<t hangText="Certificate -">The peer's certificate. Note that this
may be omitted by setting the length to zero.</t>
<t hangText="Address -">The address and port of the peer.</t>
</list>
<!--
route-log = uint16 ; number of route-log-entries
*route-log-entry
route-log-entry = route-log-p2psip-version
route-log-entry-transport
route-log-entry-peer-info
route-log-version = string
route-log-entry-transport = route-log-transport-tcp /
route-log-transport-udp /
route-log-transport-tls /
route-log-transport-dtls / uint8
route-log-transport-tcp = 1
route-log-transport-udp = 2
route-log-transport-tls = 3
route-log-transport-dtls = 4
route-log-entry-peer-info = peer-id
peer-name
peer-uptime
peer-ip-port
peer-certificate
peer-name = string ; a textual representation of the peer name
peer-ip-port = string ; a textual representation of the IP/port
peer-uptime = uint32 ; time in seconds since peer start
peer-certificate = data-value ; the peer's certificate -->
</section>
</section>
<section anchor="sec-contents" title="Message Contents Format">
<t>Although from the perspective of the forwarding layer the content
is opaque, all RELOAD messages share a common content structure
consisting of two parts:</t>
<t><list style="hanging">
<t hangText="Common Header:">A common header containing the
request method/response code, and a transaction ID.</t>
<t hangText="Payload:">The actual body of the request/response.
These are dependent on whether this is a request or response and
the type of request being carried.</t>
</list></t>
<section anchor="sec-contents-common-header" title="Common Header">
<t>The layout of the common header is shown below:</t>
<t><artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|R| | |
|/| Code | Reserved |
|r| | |
4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork></t>
<t>R/r is a one bit field used to specify if this is a request or
a response.</t>
<t><list style="empty">
<artwork><![CDATA[
REQUEST : 0x0
RESPONSE : 0x1
]]></artwork>
</list></t>
<t>Code is a 15 bit field that indicates either the message method
or the response code (depending on the value of the R/r bit)</t>
</section>
<section anchor="sec-payload" title="Payload">
<t>Payload is a simple string of uninterpreted bytes preceded by a
length field indicating the length of the data. The bytes
themselves are dependent on the code value.</t>
<t><artwork><![CDATA[
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Length |
| |
4 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
// Length bytes of data //
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
]]></artwork></t>
</section>
<section anchor="sec-signature" title="Signature">
<t>The Signature element is used to attach signatures to messages
and or stored data elements. All signatures are formatted using
this element. However, the input structure to the signature
computation varies depending on the data element being signed.</t>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
uint8 algorithm;
opaque signature_value<65000>;
signature_identity identity;
} signature;
]]></artwork>
</figure>
<t>The signature construct is just a container for the signature.
It contains the following values:</t>
<list style="hanging">
<t hangText="Algorithm -">The signature algorithm in use. This
may have the values RSA-SHA1 (0x01) or RSA-SHA-256 (0x02).</t>
<t hangText="Value - ">The signature value itself. This is just
the string of bytes emitted by the signature algorithm.</t>
<t hangText="Identity -">The identity or certificate used to
form the signature</t>
</list>
<t>A number of possible identity formats are permitted, as shown
below. The peer may indicate any of:</t>
<t>
<list style="symbols">
<t>Peer-id</t>
<t>User name</t>
<t>The certificate itself.</t>
</list>
</t>
<t>The first byte of the identity field is a type indicating the
type of identity in use.</t>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
enum {signer_identity_peer (1), signer_identity_name (2),
signer_identity_certificate (3)} signer_identity_type;
select {
case signer_identity_peer:
peer_id id;
case signer_identity_name:
string signer_name;
case signer_identity_certificate:
opaque certificate<65000>;
} signer_identity;
]]></artwork>
</figure>
<!--
signature = signature-algorithm
signer-identity
signature-value
signature-algorithm = rsa-sha1-id / rsa-sha-256-id / uint16
rsa-sha1-id = 0x01
rsa-sha256-id = 0x02
signer-identity = signer-identity-type
peer-id / signer-name / certificate / *byte
signer-identity-type = signer-identity-peer / signer-identity-name /
signer-identity-certificate / uint8
signer-identity-peer = 0x01
signer-identity-name = 0x02
signer-identity-certificate = 0x03
signer-name = string
certificate = data-value
signature = data-value
-->
<t>For signatures over messages the input to the signature
function is:</t>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
overlay overlay;
transaction_id xid;
blob signer_identity;
blob message_contents;
} message_signature_input;
]]></artwork>
</figure>
<t>The contents of this structure are as follows:</t>
<t>
<list style="hanging">
<t hangText="Overlay -">The overlay identifier from the
message.</t>
<t hangText="Xid -">The transaction id from the message.</t>
<t hangText="Signer Identity -">The identify of the signer
(from the signature structure.)</t>
<t hangText="Message Contents -">The contents section of the
message.</t>
</list>
</t>
<!--
message-signature-input = overlay ; from forwarding header
transaction-id ; from forwarding header
signer-identity
message-contents
-->
<t>[[TODO: Check the inputs to this carefully.]]</t>
<t>The input to signatures over data values is different, and is
decribed in <xref target="sec-data-sig" />.</t>
</section>
</section>
<section anchor="sec-response-code"
title="Response Codes and Response Errors">
<t>A peer processing a request returns its status in the Code field
of the common header. If the request was a success, the code should
be 200 (OK) and the payload should be as specified above. If the
request failed, then the response code should be as defined
below.</t>
<t>
<list style="hanging">
<t hangText="200 (OK):">Indicates a successful request. The
information returned in the response will depend on the request
method.</t>
<t hangText="302 (Moved Temporarily):">The requesting peer
SHOULD retry the request at the new address specified in the 302
response message.</t>
<t hangText="401 (Unauthorized):">The requesting peer needs to
sign and provide a certificate. [[TODO: The semantics here don't
seem quite right.]]</t>
<t hangText="403 (Forbidden):">The requesting peer does not have
permission to make this request.</t>
<t hangText="404 (Not Found):">The resource or peer cannot be
found or does not exist.</t>
<t hangText="408 (Request Timeout):">A response to the request
has not been received in a suitable amount of time. The
requesting peer MAY resend the request at a later time.</t>
<t hangText="412 (Precondition Failed):">A request can't be
completed because some precondition was incorrect. For instance,
the wrong generation counter was provided</t>
<t hangText="498 (Incompatible with Overlay)">A peer receiving
the request is using a different overlay, DHT algorithm, or hash
algorithm. [[Open Issue: What is the best error number and
reason phrase to use?]]</t>
<t hangText="499 (UnWilling To Proxy)">A peer receiving the
request is unwilling to support the Routing mechanism specified
in the Routing field of the message header. [[Open Issue: What
is the best error number and reason phrase to use?]]</t>
</list>
</t>
<t>For any code other than 200, the payload should be as defined
below:</t>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
string reason_phrase;
opaque error_info<65000>;
} error_response;
]]></artwork>
</figure>
<!--
error-payload = string ; reason phrase
error-payload-rest
error-payload-rest = error-payload-302 / *byte
error-payload-302 = peer-id -->
<t>The contents of this payload are:</t>
<list style="hanging">
<t hangText="Reason Phrase -">A freeform text string indicating
the reason for the response. The reason phrase SHOULD BE as
indicated in the above list (e.g., "Moved Temporarily).</t>
<t hangText="Error Info -">Payload specific error information.
This MUST be empty except as specified below.</t>
</list>
<t>For the response code 302, the error-payload-rest is the peer-id
of the peer to which the request SHOULD be redirected. This error
code is used for iterative routing.</t>
</section>
<section anchor="sec-timeout" title="Timeout and Retransmission">
<t>Timeout and retransmission are handled on an end-to-end basis.
The requesting node retransmits requests until it receives a
response or a timeout. The retransmit algorithm defined in Section
17.1.2.1 of <xref target="RFC3261"></xref> SHOULD be used.
Retransmissions MUST use the same transaction ID.</t>
</section>
</section>
<section anchor="sec-requests" title="Method Definitions">
<t>In this section, we define the initial set of methods supported by
RELOAD. New methods are defined by adding new method codes. Each method
defines the contents of the payload element (see <xref
target="sec-payload"></xref>).</t>
<section title="Connection Management">
<section title="PING">
<t>PING is used to test connectivity along a path. A ping can be
addressed to a specific peer-id or to the anycast peer-id (all 1s).
In either case, the target peer-ids respond with a simple response
containing some status information.</t>
<section title="Request Definition">
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
uint8 ping_info<255>;
} ping_request;
]]></artwork>
</figure>
<!--
ping-request = [ping-request-info-responsible]
[ping-request-info-num_resources] (uint8)*
ping-request-info-responsible = 0x01
ping-request-info-num_resource = 0x02
-->
<t>The PING request contains a list (potentially empty) of the
pieces of status information that the requester would like the
responder to provide. The two currently defined types are:</t>
<t><list style="empty">
<artwork><![CDATA[
RESPONSIBLE-SET : 0x01
NUM-RESOURCES : 0x02
]]></artwork>
</list></t>
<t>RESPONSIBLE-SET indicates that the peer should Respond with the
fraction of the overlay for which the responding peer is
responsible (in parts per billion).</t>
<t>NUM-RESOURCES indicates that the peer should Respond with the
number of resources currently being stored by the peer.</t>
</section>
<section title="Response Definition">
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
uint64 response_id;
ping_info_data infos<65000>;
} ping_response;
]]></artwork>
</figure>
<t>The ping response contains the following elements: <list
style="hanging">
<t hangText="Response ID -">A randomly generated 64-bit
response ID. This is used to distinguish PING responses in
cases where the PING request is multicast.</t>
<t hangText="Infos -">A sequence of ping info data structures,
as shown below.</t>
</list></t>
<t><figure>
<!--begin-pdu-->
<artwork><![CDATA[
enum {info_responsible_type(1),
info_num_resources_type(2)}
ping_info_types;
select {
case info_responsible_type:
uint32 responsible_ppb;
case info_num_resources_type:
uint32 num_resources;
} ping_info_select;
public struct {
ping_info_select info;
} ping_info_data;
]]></artwork>
</figure></t>
<t>The ping info data elements are simple typed elements, with a
type identifier as the leading 16 bits and then arbitrary
(type-specific) text following. In the case of the two defined
types, the responses are 32-bit integers.</t>
<!--
ping-response = ping-response-id (ping-response-value)*
ping-response-value = ping-response-info-responsible /
ping-response-info-num-resources /
ping-response-info-any
ping-response-info-responsible = ping-request-info-responsible
0x04
uint32 ; parts per billion
ping-response-info-num-resources = ping-request-info-num-resources
0x04
uint32 ; count
ping-response-info-any = uint8
uint8
*byte
-->
<t>The responding peer SHOULD include any values that the
requesting peer requested and that it recognizes. They SHOULD be
returned in the requested order.</t>
</section>
</section>
<section anchor="sec-connect-details" title="CONNECT">
<t>A node sends a CONNECT request when it wishes to establish a
direct TCP or UDP connection to another node for the purposes of
sending RELOAD messages or application layer protocol messages, such
as SIP. Detailed procedures for the CONNECT and its response are
described in <xref target="sec-connect-ice" />.</t>
<note title="Note">
<t>A CONNECT does not result in updating the routing table of
either node. That function is performed by UPDATEs. If node A has
CONNECTed to node B, it MAY route messages which are directly
addressed to B through that channel but MUST NOT route messages
through B to other peers via that channel.</t>
</note>
<section anchor="sec-connect-request" title="Request Definition">
<t>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
string ufrag;
string password;
uint16 application;
string fingerprint;
string role;
candidate candidate_list<65000>;
} connect_data;
public struct {
string candidate_string;
} candidate;
]]></artwork>
</figure>
<!--
connect-data = connect-ufrag
connect-password
connect-application
connect-fingerprint
connect-actpass
1*connect-attribute
connect-ufrag = string ; ICE "password"
connect-password = string ; ICE "ufrag"
connect-application = uint16 ; an IANA registered port number
connect-fingerprint = string ; RFC 4572 "fingerprint"
connect-actpass = string ; RFC 4145 "role"
;
connect-attribute = string ; ICE candidate
-->
</t>
<t>The values contained in connect-request are:</t>
<t>
<list style="hanging">
<t hangText="Ufrag -">The username fragment (from ICE)</t>
<t hangText="Password -">The ICE password.</t>
<t hangText="Application -">A 16-bit port number. This port
number represents the IANA registered port of the protocol
that is going to be sent on this connection. For SIP, this is
5060 or 5061, and for RELOAD is TBD. By using the IANA
registered port, we avoid the need for an additional registry
and allow RELOAD to be used to set up connections for any
existing or future application protocol.</t>
<t hangText="Fingerprint -">One fingerprint attribute (from
RFC 4572 <xref target="RFC4572" />.</t>
<t hangText="Role -">An active/passive/actpass attribute from
RFC 4145 <xref target="RFC4145" />.</t>
<t hangText="Candidate -">One or more ICE candidate values.
Each candidate has an IP address, IP address family, port,
transport protocol, priority, foundation, component ID, STUN
type and related address. The candidate_list is a list of
string candidate values.</t>
</list>
</t>
<t>These values should be generated using the procedures of <xref
target="sec-connect-ice" />.</t>
</section>
<section anchor="sec-connect-response" title="Response Definition">
<t>If a peer receives a CONNECT request, it SHOULD follow the
procedures of <xref target="sec-connect-ice" /> to process the
request and generate its own response, containing a connect-data
production. It should then begin ICE checks. When a peer receives
a CONNECT response, it SHOULD parse the response and begin its own
ICE checks.</t>
</section>
</section>
<section anchor="sec-tunnel-details" title="TUNNEL">
<t>A node sends a TUNNEL request when it wishes to exchange
application-layer protocol messages without the expense of
establishing a direct connection via CONNECT or when ICE is unable
to establish a direct connection via CONNECT and a TURN relay is not
available. The application-level protocols that are routed via the
TUNNEL request are defined by that application's usage.</t>
<note title="Note">
<t>The decision of whether to route application-level traffic
across the overlay or to open a direct connection requires careful
consideration of the overhead involved in each transaction.
Establishing a direct connection requires greater initial setup
costs, but after setup, communication is faster and imposes no
overhead on the overlay. For example, for the SIP usage, an INVITE
to establish a voice call might be routed over the overlay, a
SUBSCRIBE with regular updates would be better used with a
CONNECT, and media would both impose too great a load on the
overlay and likely receive unacceptable performance. However,
there may be a tradeoff between locating TURN servers and relying
on TUNNEL for packet routing.</t>
</note>
<t>When a usage requires the TUNNEL method, it must specify the
specific application protocol(s) that will be TUNNELed and for each
protocol, specify: <list style="symbols">
<t>An application attribute that indicates the protocol being
tunneled. This the IANA-registered port of the application
protocol.</t>
<t>The conditions under which the application will be TUNNELed
over the overlay rather than using a direct CONNECT.</t>
<t>A mechanism for moving future application-level communication
from TUNNELing on the overlay to a direct CONNECTion, or an
explanation why this is unnecessary.</t>
<t>A means of associating messages together as required for
dialog-oriented or request/response-oriented protocols.</t>
<t>How the TUNNELed message (and associated responses) will be
delivered to the correct application. This is particularly
important if there might be multiple instances of the
application on or behind a single peer.</t>
</list></t>
<section anchor="sec-tunnel-request" title="Request Definition">
<t>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
uint16 application;
string dialog_id;
string application_pdu;
} tunnel_data;
]]></artwork>
</figure>
</t>
<t>For each of the values indicated here which were originally
text, they are preceded by a length field of either one or two
bytes.</t>
<t>The values contained in connect-request are:</t>
<t>
<list style="hanging">
<t hangText="Application -">A 16-bit port number. This port
number represents the IANA registered port of the protocol
that is going to be sent on this connection. For SIP, this is
5060 or 5061, and for RELOAD is TBD. By using the IANA
registered port, we avoid the need for an additional registry
and allow RELOAD to be used to set up connections for any
existing or future application protocol.</t>
<t hangText="Dialog ID -">An arbitrary string providing an
application-defined way of associating related TUNNELed
messages. This attribute may also encode sequence information
as required by the application protocol.</t>
<t hangText="Application PDU -">An application PDU in the
format specified by the application.</t>
</list>
</t>
</section>
<section anchor="sec-tunnel-response" title="Response Definition">
<t>A TUNNEL response serves as confirmation that the message was
received by the destination peer. It implies nothing about the
processing of the application. If the application protocol
specifies an acknowledgement or confirmation, that must be sent
with a separate TUNNEL request</t>
</section>
</section>
</section>
<section title="Data Storage and Retrieval">
<t>The STORE, FETCH, and REMOVE methods are used to manipulate
information in the DHT. They form an instantiation of the abstract GET
and PUT operations described in <xref
target="I-D.ietf-p2psip-concepts"></xref>.</t>
<section anchor="sec-store" title="STORE">
<t>The STORE method is used to store data in the overlay. As
described in <xref target="sec-typed-data"></xref> each location may
contain data of multiple types. Each type-id is a code point
assigned to a specific application usage by IANA. As part of the
Usage definition, protocol designers may define constraints, such as
limits on size, on the values which may be stored. For many types,
the set may be restricted to a single item; some sets may be allowed
to contain multiple identical items while others may only have
unique items. The protocol currently defines the following data
models:</t>
<t><list style="symbols">
<t>single value</t>
<t>array</t>
<t>dictionary</t>
</list></t>
<t>Each type-id MUST specify the appropriate data model for that
type. The format of the STORE request depends on the data model.</t>
<section anchor="sec-store-req" title="Request Definition">
<t>A STORE production is a sequence of type-data pairs, each of
which represents a sequence of stored values for a given type-id.
The same type-id MUST NOT be used twice in a given store request.
Each value is then processed in turn. These operations MUST be
atomic. If any operation fails, the state MUST be rolled back to
before the request was received.</t>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
resource_id resource;
store_type_data store_data<65000>;
} store_request;
]]></artwork>
</figure>
<t>A single STORE request stores data of a number of types to a
single resource location. The contents of the request are:</t>
<list style="hanging">
<t hangText="Resource -">The resource to store at.</t>
<t hangText="Store Type Data -">A series of elements, one for
each type of data to be stored.</t>
</list>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
type_id type;
generation_counter generation;
stored_data values<65000>;
} store_type_data;
]]></artwork>
</figure>
<t>Each store type data element represents the data to be stored
for a single type-id. The contents of the element are:</t>
<list style="hanging">
<t hangText="Type -">The type-id</t>
<t hangText="Generation -">The expected current state of the
generation counter.</t>
<t hangText="Values -">The value or values to be stored. This
may contain one or more stored_data values depending on the data
model associated with each type-id.</t>
</list>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
uint32 length;
uint32 storage_time;
uint32 lifetime;
blob data-value;
blob signature;
} stored_data;
]]></artwork>
</figure>
<t>Each stored_data element represents a single stored data value.
These elements are individually signed. The contents of the
element are as follows:</t>
<list style="hanging">
<t hangText="Length -">The length of the stored data
element.</t>
<t hangText="Storage Time -">The time when the data was stored
in absolute time, represented in seconds since the Unix epoch.
Any attempt to store a data value with a storage time before
that of a value known to the receiving peer MUST generate a 412
error. This prevents rollback attacks. Note that this does not
require synchronized clocks: the receiving peer uses the storage
time in the previous store, not its own clock.</t>
<t hangText="Lifetime -">The validity period for the data, in
seconds, starting from the time of store.</t>
<t hangText="Signature -">A signature over the data value. <xref
target="sec-data-sig" /> describes the signature computation.
The element is formatted as described in <xref
target="sec-signature" /></t>
<t hangText="Data Value -">The data value itself, as described
below.</t>
</list>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
opaque value<65000>;
} single_value_entry;
public struct {
int32 index;
opaque value<65000>;
} array_entry;
public struct {
opaque key<65000>;
opaque value<65000>;
} dictionary_entry;
]]></artwork>
</figure>
<!-- store-request = resource-id 1*store-type-data
store-type-data = type-id
generation-counter
uint16 ; number of stored data elements
1*stored-data
generation-counter = uint64
stored-data = uint32 ; length of the rest of the production
stored-data-expiry-time
stored-data-value
signature
stored-data-value = single-value / array-entry / dictionary-entry /
*byte
single-value = data-value
data-value = uint32 ; length
*byte ; data
array-entry = int32 ; index
data-value
dictionary-entry = data-value ; key
data-value ; value
-->
<t>The responsible peer MUST perform the following checks:</t>
<t>
<list style="symbols">
<t>The type-id is known.</t>
<t>The signature over the message is valid or (depending on
overlay policy) no signature is required.</t>
<t>The signatures over each individual data element (if any)
are valid.</t>
<t>Each element is signed by a credential which is authorized
to write this type at this resource-id</t>
<t>If the generation-counter is non-zero, it must equal the
current value of the generation-counter for this type. This
feature allows the generation counter to be used in a way
similar to the HTTP Etag feature.</t>
<t>The storage time values are greater than that of any value
which would be replaced by this STORE. [[OPEN ISSUE: do peers
need to save the storage time of REMOVEs to prevent
reinsertion?]]</t>
</list>
</t>
<t>If all these checks succeed, the peer MUST attempt to store the
data values. If the store succeeds and the data is changed, then
the peer must increase the generation counter by at least one. If
there are multiple stored values in a single store-type-data, it
is permissible for the peer to increase the generation counter by
only 1 for the entire type-id, or by 1 or more than one for each
value.</t>
<t>We now discuss each type of value.</t>
<section title="Single Value">
<t>There may be only one single-value element for each
resource-id, type pair. A store of a new single-value element
MUST overwrite the current value.</t>
</section>
<section title="Array">
<t>A store of an array entry replaces (or inserts) the given
value at the location specified by the index. Arrays are
zero-based. Note that arrays can be sparse. Thus, a store of "X"
at index 2 in an empty array produces an array with the values [
NA, NA, "X"]. Future attempts to fetch elements at index 0 or 1
will return empty strings. If the index value is -1, then the
value is placed at the end of the array.</t>
</section>
<section title="Dictionary">
<t>A stored dictionary entry has a dictionary-key used as a
lookup key and a dictionary-value containing the data. There may
be only one value any given dictionary-key and therefore a write
to a dictionary-key overwrites whatever is there.</t>
</section>
</section>
<section title="Response Definition">
<t>In response to a successful STORE request the peer MUST return
a series of store_type_response elements containing the current
value of the generation counter for each type-id.</t>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
type_id type;
generation_counter generation;
} store_type_response;
]]></artwork>
</figure>
<!--
store-response = 1*store-type-response
store-type-response = type-id generation-counter
-->
<t>The contents of each element are:</t>
<list style="hanging">
<t hangText="Type -">The type-id being represented.</t>
<t hangText="Generation -">The current value of the generation
counter for that type-id.</t>
</list>
<t>The response itself is just the store_type_response values
packed end-to-end.</t>
<t>If the request was rejected because of an invalid generation
counter, then the store-response MUST also be returned, but with a
response code of 412. Otherwise, the response MAY contain a
response-error-reason production or MAY be empty. [[TODO: The
generation counter may need more thinking for uniqueness.]]</t>
</section>
<section anchor="sec-data-sig" title="Data Signature Computation">
<t>Each stored-data element is individually signed. However, the
signature also must be self-contained and cover the type-id and
resource-id even though they are not present in the stored value.
The data signed is defined as:</t>
<t>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
resource_id resource;
type_id type;
blob stored_data;
} stored_data_to_be_signed;
]]></artwork>
</figure>
</t>
<!-- stored-data-to-be-signed = resource-id type-id stored-data -->
<t>The contents of this value are as follows:</t>
<list style="hanging">
<t hangText="Resource -">The resource ID where this data is
stored.</t>
<t hangText="Type -">The type-id for this data.</t>
<t hangText="Stored Data -">The contents of the stored data
value, as described in the stored_data PDU of <xref
target="sec-store-req" /></t>
</list>
<t>[[TODO: Should we include the identity?.]]</t>
<t>Once the signature has been computed, the signature is
represented using a signature element, as described in <xref
target="sec-signature" />.</t>
</section>
</section>
<section title="FETCH">
<t>The FETCH request retrieves one or more data elements stored at a
given resource-id.</t>
<section title="Request Definition">
<t>The request consists of a single fetch_request element followed
by a series of fetch_type_data elements. <figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
resource_id resource;
fetch_type_data fetch_data<65000>;
} fetch_request;
]]></artwork>
</figure> <t> The contents of the request are as follows: </t>
<list style="hanging">
<t hangText="Resource -">The resource ID to fetch from.</t>
<t hangText="Fetch Data -">A sequence of data specifiers, one
for each desired type ID.</t>
</list> <t> Each fetch_type_data element is specified as
follows. </t> <figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
type_id type;
generation_counter generation;
fetch_data_reference reference;
} fetch_type_data;
]]></artwork>
</figure></t>
<list style="hanging">
<t hangText="Type -">The type of the data being fetched.</t>
<t hangText="Generation -">The last generation counter that the
requesting peer saw. This is used to avoid unnecessary
fetches.</t>
<t hangText="Reference -">A reference to the data value being
requested within the data model specified for the type, as
specified below.</t>
</list>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
int32 first;
int32 last;
} fetch_array_reference;
public struct {
dictionary_key dictionary_keys<65000>;
} fetch_dictionary_reference;
public struct {
string key_value<65000>;
} dictionary_key;
]]></artwork>
</figure>
<!--
enum {fetch_single_type(1), fetch_array_type(2), fetch_dictionary_type(3)} fetch_type;
select {
case fetch_array_type:
fetch_array_reference array_ref;
case fetch_dictionary_type:
fetch_dictionary_reference dictionary_ref;
} fetch_data_reference;
-->
<!-- fetch-request = resource-id 1*fetch-type-data
fetch-type-data = type-id
generation-counter
fetch-data-reference
fetch-data-reference = array-reference / dictionary-reference / *byte
array-reference = int32 int32
dictionary-reference = uint32 ; number of keys
*data-value ; list of dictionary keys-->
<t>As with STORE, the fetch request contains a list of type-ids
and associated references. The reference encoding depends on the
type of value being stored.</t>
<list style="symbols">
<t>If the data is of type single value, the reference is
empty.</t>
<t>If the data is of type array, the reference contains two
integers. The first integer is the beginning of the range and
the second is the end of the range. 0 is used to indicate the
first element and -1 is used to indicate the final element. The
beginning of the range MUST be earlier in the array then the
end.</t>
<t>If the data is of type dictionary then the reference contains
a list of the dictionary keys being requested. If no keys are
specified, than this is a wildcard fetch and all key-value pairs
should be returned.</t>
</list>
<t>The generation-counter is used to indicate the requester's
expected state of the storing peer. If the generation-counter in
the request matches the stored counter, then the storing peer
returns a cache hit indicator rather than the stored data.</t>
<t>Note that because the certificate for a user is typically
stored at the same location as any data stored for that user, a
requesting peer which does not already have the user's certificate
should request the certificate in the FETCH as an
optimization.</t>
</section>
<section title="Response Definition">
<t><figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
type_id type;
generation_counter generation;
opaque stored_data<65000>;
} fetch_response;
]]></artwork>
</figure></t>
<!--
fetch-response = 1*fetch-type-value
fetch-type-value = type-id
generation-counter
uint16 ; number of stored data elements
1*stored-data
-->
<t>There MUST be one fetch_type_data element for each type-id in
the request. If the generation-counter in the request matches the
generation-counter in the stored data, then the count of stored
data elements MUST be zero. Otherwise, all relevant data values
MUST be returned. A nonexistent value is represented as a value
with an empty data value portion and no signature. In particular,
if a dictionary key that does not exist is requested, then there
must be a dictionary entry with that key but an empty value.</t>
</section>
</section>
<section title="REMOVE">
<t>The REMOVE request is used to remove a stored element or elements
from the storing peer. Although each type-id defines its own access
control requirements, in general only the original signer of the
data should be allowed to remove it. Any successful remove of an
existing element for a given type-id MUST increment the generation
counter by at least one.</t>
<t>A remove-request has exactly the same syntax as a FETCH request
except that each entry represents a set of values to be removed
rather than returned. The same type-id MUST NOT be used twice in a
given remove-request. Each fetch-type-data is then processed in
turn. These operations MUST be atomic. If any operation fails, the
state MUST be rolled back to before the request was received.</t>
<t>Before processing the REMOVE request, the peer MUST perform the
following checks.</t>
<t><list style="symbols">
<t>The type-id is known.</t>
<t>The signature over the message is valid or (depending on
overlay policy) no signature is required.</t>
<t>The signer of the message has permissions which permit him to
remove this type of data.</t>
<t>If the generation-counter is non-zero, it must equal the
current value of the generation-counter for this type. This
feature allows the generation counter to be used in a way
similar to the HTTP Etag feature.</t>
</list></t>
<t>Assuming that the request is permitted, the operations proceed as
follows.</t>
<section title="Single Value">
<t>A REMOVE of a single value element simple causes it not to
exist. If no such element exists, then this simply is a silent
success.</t>
</section>
<section title="Array">
<t>A REMOVE of an array element (or element range) replaces those
elements with empty elements. Note that this does not cause the
array to be packed. An array which contains ["A", "B", "C"] and
then has element 0 removed produces an array containing [NA, "B",
"C"]. Note, however, that the removal of the final element of the
array shortens the array, so in the above case, the removal of
element 2 makes the array ["A", "B"].</t>
</section>
<section title="Dictionary">
<t>A REMOVE of a dictionary element (or elements) replaces those
elements with empty elements. If no such elements exist, then this
is a silent success.</t>
</section>
<section title="Response Definition">
<t>The response to a successful REMOVE simply contains a list of
the new generation counters for each type-id, using the same
syntax as the response to a STORE request. Note that if the
generation counter does not change, that means that the requested
items did not exist. However, if the generation counter does
change, that does not mean that the items existed.</t>
</section>
</section>
<section title="FIND">
<t>The FIND request is used to explore the DHT. A FIND request for a
resource-id R and a type-id T retrieves the resource-id (if any) of
the resource of type T known to the target peer which is closes to
R. This method can be used to walk the DHT by interactively fetching
R_n+1=nearest(1 + R_n).</t>
<section title="Request Definition">
<t>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
resource_id resource;
type_id ids<255>;
} find_request;
]]></artwork>
</figure>
</t>
<!-- find-request = resource-id 1*type-id -->
</section>
<t>The request contains a list of type-ids which the FIND is for, as
indicated below.</t>
<list style="hanging">
<t hangText="Resource -">The desired resource-id</t>
<t hangText="Ids -">The desired type-ids. Each value MUST only
appear once.</t>
</list>
<section title="Response Definition">
<t>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
type_id type;
resource_id closest_resource;
} find_type_data;
]]></artwork>
</figure>
</t>
<t>If the processing peer is not responsible for the specified
resource-id, it SHOULD return a 404 error.</t>
<t>When each type is defined, it can indicate if the type is not
allowed to be used in a FIND request. This would be done to help
achieve some types of security properties for the data stored in
that type.</t>
<t>For each type-id in the request the response MUST contain a
find-response-value indicating the closest resource-id for that
type-id unless the type is not allowed to be used with FIND in
which case a find_type_data for that type_id MUST NOT be included
in the response. If a type-id is not known, then the corresponding
resource-id MUST be 0. Note that different type-ids may have
different closest resource-ids.</t>
<t>The response is simply a series of find_type_data elements, one
per type, concatenated end-to-end. The contents of each element
are:</t>
<list style="hanging">
<t hangText="Type -">The type-id.</t>
<t hangText="Closest Resource -">The closest resource ID to the
specified resource ID. This is 0 if no resource ID is known.</t>
</list>
<t>Note that the response does not contain the contents of the
data stored at these resource-ids. If the requester wants this, it
must retrieve it using FETCH.</t>
</section>
</section>
</section>
<section anchor="sec-dht-maint" title="DHT Maintenance">
<t>This section describes methods that are expected to be useful for
all DHTs. These methods have generic semantics (join, leave, update)
and some common fields, but where appropriate allow room for
DHT-specific data.</t>
<section title="JOIN">
<t>A new peer (but which already has credentials) uses the JOIN
message to join the DHT. The JOIN is sent to the peer which
previously was responsible for the resource-id corresponding to the
peer-id which the new peer has. This notifies the responsible peer
that the new peer is taking over some of the overlay and it needs to
synchronize its state.</t>
<t><figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
peer_id desired_peer_id;
blob dht_specific_data;
} join_request;
]]></artwork>
</figure></t>
<!-- join-request = peer-id -->
<t>The default JOIN request contains only the peer-id which the
sending peer wishes to assume. DHTs MAY specific other data to
appear in this request.</t>
<t>By default, responding peer simply responds with success or
failure. However, if it is success it MUST follow up by executing
the right sequence of STOREs and UPDATEs to transfer the appropriate
section of the overlay space to the joining peer. In addition, DHTs
MAY define data to appear in the response payload.</t>
</section>
<section title="LEAVE">
<t>The LEAVE message is used to indicate that a peer is exiting the
overlay. The peer SHOULD send this message to each peer with which
it is directly connected prior to exiting the overlay.</t>
<t><figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
peer_id leaving_peer_id;
blob dht_specific_data;
} leave_request;
]]></artwork>
</figure></t>
<!-- leave-request = peer-id -->
<t>The default LEAVE request contains only the peer-id of the
leaving peer. DHTs MAY specific other data to appear in this
request.</t>
<t>Upon receiving LEAVE, a peer MUST update its own routing and
routing table, and send the appropriate STORE/UPDATE sequences to
restabilize the overlay.</t>
</section>
<section title="UPDATE">
<t>Update is the primary DHT-specific maintenance message. It is
used by the sender to notify the recipient of the sender's view of
the current state of the overlay and it is up to the recipient to
take whatever actions are appropriate to deal with the state
change.</t>
<t>The contents of the UPDATE request are completely DHT-specific.
The UPDATE response is expected to be either success or an
error.</t>
</section>
</section>
</section>
<section anchor="sec-connect-ice" title="ICE and Connection Formation">
<t>At numerous times during the operation of RELOAD, a node will need to
establish a connection to another node. This may be for the purposes of
building finger tables when the node joins the P2P network, or when the
node learns of a new neighbor through an UPDATE and needs to establish a
connection to that neighbor.</t>
<t>In addition, a node may need to connect to another node for the
purposes of an application connection. In the case of SIP, when a node
has looked up the target AOR in the DHT, it will obtain a Node-ID that
identifies that peer. The next step will be to establish a "direct"
connection for the purposes of performing SIP signaling.</t>
<t>In both of these cases, the node starts with a destination Node-ID,
and its objective is to create a connection (ideally using TCP, but
falling back to UDP when it is not available) to the node with that
given Node-ID. The establishment of this connection is done using the
CONNECT request in conjunction with ICE. It is assumed that the reader
has familiarity with ICE.</t>
<t>RELOAD implementations MUST implement full ICE. Because RELOAD always
tries to use TCP and then UDP as a fallback, there will be multiple
candidates of the same IP version, which requires full ICE.</t>
<section title="Overview">
<t>To utilize ICE, the CONNECT method provides a basic offer/answer
operation that exchanges a set of candidates for a single "stream". In
this case, the "stream" refers not to RTP or other types of media, but
rather to a connection for RELOAD itself or for SIP signaling. The
CONNECT request contains the candidates for this stream, and the
CONNECT response contains the corresponding answer with candidates for
that stream. Though CONNECT provides an offer/answer exchange, it does
not actually carry or utilize Session Description Protocol (SDP)
messages. Rather, it carries the raw ICE parameters required for ICE
operation, and the ICE spec is utilized as if these parameters had
actually been used in an SDP offer or answer. In essence, ICE is
utilized by mapping the CONNECT parameters into an SDP for the
purposes of following the details of ICE itself. That avoids the need
for RELOAD to respecify ICE, yet allows it to operate without the
baggage that SDP would bring.</t>
<t>In addition, RELOAD only allows for a single offer/answer exchange.
Unlike the usage of ICE within SIP, there is never a need to send a
subsequent offer to update the default candidates to match the ones
selected by ICE.</t>
<t>RELOAD and SIP always run over TLS for TCP connections and DTLS
<xref target="RFC4347"></xref> for UDP "connections". Consequently,
once ICE processing has completed, both agents will begin TLS and DTLS
procedures to establish a secure link. Its important to note that, had
a TURN server been utilized for the TCP or UDP stream, the TURN server
will transparently relay the TLS messaging and the encrypted TLS
content, and thus will not have access to the contents of the
connection once it is established. Any attack by the TURN server to
insert itself as a man-in-the-middle are thwarted by the usage of the
fingerprint mechanism of RFC 4572 <xref target="RFC4572"></xref>,
which will reveal that the TLS and DTLS certificates are not a match
for the ones used to sign the RELOAD messages.</t>
<t>An agent follows the ICE specification as described in <xref
target="I-D.ietf-mmusic-ice"></xref> and <xref
target="I-D.ietf-mmusic-ice-tcp"></xref> with the changes and
additional procedures described in the subsections below.</t>
</section>
<section anchor="sec-collect" title="Collecting STUN Servers">
<t>ICE relies on the node having one or more STUN servers to use. In
conventional ICE, it is assumed that nodes are configured with one or
more STUN servers through some out-of-band mechanism. This is still
possible in RELOAD but RELOAD also learns STUN servers as it connects
to other peers. Because all RELOAD peers implement ICE and use STUN
keepalives, every peer is a STUN server<xref
target="I-D.ietf-behave-rfc3489bis"></xref>. Accordingly, any peer you
know about will be willing to be a STUN server for you -- though of
course it may be behind a NAT.</t>
<t>A peer on a well-provisioned wide-area overlay will be configured
with one or more bootstrap peers. These peers make an initial list of
STUN servers. However, as the peer forms connections with additional
peers, it builds more peers it can use as STUN servers.</t>
<t>Because complicated NAT topologies are possible, a peer may need
more than one STUN server. Specifically, a peer that is behind a
single NAT will typically observe only two IP addresses in its STUN
checks: its local address and its server reflexive address from a STUN
server outside its NAT. However, if there are more NATs involved, it
may discover that it learns additional server reflexive addresses
(which vary based on where in the topology the STUN server is). To
maximize the chance of achieving a direct connection, A peer SHOULD
group other peers by the peer-reflexive addresses it discovers through
them. It SHOULD then select one peer from each group to use as a STUN
server for future connections.</t>
<t>Only peers to which the peer currently has connections may be used.
If the connection to that host is lost, it MUST be removed from the
list of stun servers and a new server from the same group SHOULD be
selected.</t>
<t>OPEN ISSUE: should the peer try to keep at least one peer in each
group, even if it has no other reason for the connection? Need to
specify when to stop adding new groups if the peer is behind a really
bad NAT.</t>
<t>OPEN ISSUE: RELOAD-01 had a Peer-Info structure that allowed peers
to exchange information such as a "default" IP-port pair in UPDATEs.
This structure could be expanded to include the candidate list for a
peer, thus allowing ICE negotiation to begin or even direct
communication before a CONNECT request has been received. (The
candidate pairs for the P2P port are fixed because the same source
port is used for all connections.) However, because this would require
significant changes to the ICE algorithm, we have not introduced such
an extension at this point.</t>
</section>
<section anchor="sec-gather" title="Gathering Candidates">
<t>When a node wishes to establish a connection for the purposes of
RELOAD signaling or SIP signaling (or any other application protocol
for that matter), it follows the process of gathering candidates as
described in Section 4 of ICE <xref
target="I-D.ietf-mmusic-ice"></xref>. RELOAD utilizes a single
component, as does SIP. Consequently, gathering for these "streams"
requires a single component.</t>
<t>An agent MUST implement ICE-tcp <xref
target="I-D.ietf-mmusic-ice"></xref>, and MUST gather at least one UDP
and one TCP host candidate for RELOAD and for SIP.</t>
<t>The ICE specification assumes that an ICE agent is configured with,
or somehow knows of, TURN and STUN servers. RELOAD provides a way for
an agent to learn these by querying the ring, as described in <xref
target="sec-collect"></xref> and <xref
target="sec-stun-turn-usage"></xref>.</t>
<t>The agent SHOULD prioritize its TCP-based candidates over its
UDP-based candidates in the prioritization described in Section 4.1.2
of ICE <xref target="I-D.ietf-mmusic-ice"></xref>.</t>
<t>The default candidate selection described in Section 4.1.3 of ICE
is ignored; defaults are not signaled or utilized by RELOAD.</t>
</section>
<section title="Encoding the CONNECT Message">
<t>Section 4.3 of ICE describes procedures for encoding the SDP.
Instead of actually encoding an SDP, the candidate information (IP
address and port and transport protocol, priority, foundation,
component ID, type and related address) is carried within the
attributes of the CONNECT request or its response. Similarly, the
username fragment and password are carried in the CONNECT message or
its response. <xref target="sec-connect-details"></xref> describes the
detailed attribute encoding for CONNECT. The CONNECT request and its
response do not contain any default candidates or the ice-lite
attribute, as these features of ICE are not used by RELOAD. The
CONNECT request and its response also contain a Next-Protocol
attribute, with a value of SIP or RELOAD, which indicates what
protocol is to be run over the connection. The RELOAD CONNECT request
MUST only be utilized to set up connections for application protocols
that can be multiplexed with STUN and RELOAD itself.</t>
<t>Since the CONNECT request contains the candidate information and
short term credentials, it is considered as an offer for a single
media stream that happens to be encoded in a format different than
SDP, but is otherwise considered a valid offer for the purposes of
following the ICE specification. Similarly, the CONNECT response is
considered a valid answer for the purposes of following the ICE
specification.</t>
<t>Since all messages with RELOAD are secured between nodes, the node
MUST implement the fingerprint attribute of RFC 4572 <xref
target="RFC4572"></xref>, and encode it into the CONNECT request and
response as described in <xref target="sec-connect-details"></xref>.
This fingerprint will be matched with the certificates utilized to
authenticate the RELOAD CONNECT request and its response.</t>
<t>Similarly, the node MUST implement the active, passive, and actpass
attributes from RFC 4145 <xref target="RFC4145"></xref>. However, here
they refer strictly to the role of active or passive for the purposes
of TLS handshaking. The TCP connection directions are signaled as part
of the ICE candidate attribute.</t>
</section>
<section title="Verifying ICE Support">
<t>An agent MUST skip the verification procedures in Section 5.1 and
6.1 of ICE. Since RELOAD requires full ICE from all agents, this check
is not required.</t>
</section>
<section title="Role Determination">
<t>The roles of controlling and controlled as described in Section 5.2
of ICE are still utilized with RELOAD. However, the offerer (the
entity sending the CONNECT request) will always be controlling, and
the answerer (the entity sending the CONNECT response) will always be
controlled. The connectivity checks MUST still contain the
ICE-CONTROLLED and ICE-CONTROLLING attributes, however, even though
the role reversal capability for which they are defined will never be
needed with RELOAD. This is to allow for a common codebase between ICE
for RELOAD and ICE for SDP.</t>
</section>
<section title="Connectivity Checks">
<t>The processes of forming check lists in Section 5.7 of ICE,
scheduling checks in Section 5.8, and checking connectivity checks in
Section 7 are used with RELOAD without change.</t>
</section>
<section title="Concluding ICE">
<t>The controlling agent MUST utilize regular nomination. This is to
ensure consistent state on the final selected pairs without the need
for an updated offer, as RELOAD does not generate additional
offer/answer exchanges.</t>
<t>The procedures in Section 8 of ICE are followed to conclude ICE,
with the following exceptions:</t>
<t><list style="symbols">
<t>The controlling agent MUST NOT attempt to send an updated offer
once the state of its single media stream reaches Completed.</t>
<t>Once the state of ICE reaches Completed, the agent can
immediately free all unused candidates. This is because RELOAD
does not have the concept of forking, and thus the three second
delay in Section 8.3 of ICE does not apply.</t>
</list></t>
</section>
<section title="Subsequent Offers and Answers">
<t>An agent MUST NOT send a subsequent offer or answer. Thus, the
procedures in Section 9 of ICE MUST be ignored.</t>
</section>
<section title="Media Keepalives">
<t>STUN MUST be utilized for the keepalives described in Section 10 of
ICE.</t>
</section>
<section title="Sending Media">
<t>The procedures of Section 11 apply to RELOAD as well. However, in
this case, the "media" takes the form of application layer protocols
(RELOAD or SIP for example) over TLS or DTLS. Consequently, once ICE
processing completes, the agent will begin TLS or DTLS procedures to
establish a secure connection. The fingerprint from the CONNECT
request and its response are used as described in RFC 4572 <xref
target="RFC4572"></xref>, to ensure that another node in the P2P
network, acting as a TURN server, has not inserted itself as a
man-in-the-middle. Once the TLS or DTLS signaling is complete, the
application protocol is free to use the connection.</t>
<t>The concept of a previous selected pair for a component does not
apply to RELOAD, since ICE restarts are not possible with RELOAD.</t>
</section>
<section title="Receiving Media">
<t>An agent MUST be prepared to receive packets for the application
protocol (TLS or DTLS carrying RELOAD, SIP or anything else) at any
time. The jitter and RTP considerations in Section 11 of ICE do not
apply to RELOAD or SIP.</t>
</section>
</section>
<!-- <section title="DHT Algorithms">
<t>This section describes what needs to be specified when specifying a
new DHT Algorithm.</t>
<t>Describe this from point of view of event driven system. Events
include a user deciding to join, leave, etc. and protocol events such as
receive update, join, etc. When an event is received, DHT defines a
series of things to send and things to store - the DHT algorithm
specifies what message gets sent on each event and what gets stored.</t>
<section title="Generic Algorithm Requirements">
<t>TODO</t>
<t><list style="symbols">
<t>How to store redundant encoding</t>
<t>Algorithm to go from a seed, such as a user name, to a
Resource-ID</t>
<t>Joining procedures</t>
<t>Stabilization procedures</t>
<t>Exit procedures</t>
<t>Keep alive procedures</t>
<t>Routing and loops</t>
<t>Merging procedures to recovering from network partitions</t>
<t>Detecting disconnection from rest of peers</t>
</list></t>
</section>
</section>
-->
<section title="Chord Algorithm ">
<t></t>
<t>This algorithm is assigned the name chord-128-2-8 to indicate it is
based on Chord, uses a 128 bit hash function, stores 2 redundant copies
of all data, and has finger tables with 8 entries.</t>
<section title="Overview">
<t>The algorithm described here is a modified version of the Chord
algorithm. Each peer keeps track of a finger table of 8 entries and a
neighborhood table of 6 entries. The neighborhood table contains the 3
peers before this peer and the 3 peers after it in the DHT ring. The
first entry in the finger table contains the peer half-way around the
ring from this peer; the second entry contains the peer that is 1/4 of
the way around; the third entry contains the peer that is 1/8th of the
way around, and so on. Fundamentally, the chord data structure can be
thought of a doubly-linked list formed by knowing the successors and
predecessor peers in the neighborhood table, sorted by the peer-id. As
long as the successor peers are correct, the DHT will return the
correct result. The pointers to the prior peers are kept to enable
inserting of new peers into the list structure. Keeping multiple
predecessor and successor pointers makes it possible to maintain the
integrity of the data structure even when consecutive peers
simultaneously fail. The finger table forms a skip list, so that
entries in the linked list can rapidly be found - it needs to be there
so that peers can be found in O(log(N)) time instead of the typical
O(N) time that a linked list would provide.</t>
<t>A peer, n, is responsible for a particular Resource-ID k if k is
less than or equal to n and k is greater than p, where p is the peer
id of the previous peer in the neighborhood table. Care must be taken
when computing to note that all math is modulo 2^128.</t>
</section>
<section title="Routing">
<t>If a peer is not responsible for a Resource-ID k, then it routes a
request to that location by routing it to the peer in either the
neighborhood or finger table that has the largest peer-id that is
still less than or equal to k.</t>
</section>
<section title="Redundancy ">
<t>When a peer receives a STORE request for Resource-ID k, and it is
responsible for Resource-ID k, it stores the data and returns a
SUCCESS response. [[Open Issue: should it delay sending this SUCCESS
until it has successfully stored the redundant copies?]]. It then
sends a STORE request to its successor in the neighborhood table and
to that peers successor. Note that these STORE requests are addressed
to those specific peers, even though the Resource-ID they are being
asked to store is outside the range that they are responsible for. The
peers receiving these check they came from an appropriate predecessor
in their neighborhood table and that they are in a range that this
predecessor is responsible for, and then they store the data.</t>
<note title="Note: ">
<t>This redundancy algorithm breaks if the storing node is malicious
and does not store the data in the replica set. Applications which
wish to have defenses against that must explicitly store multiple
copies of the data with separate peers. [[OPEN ISSUE: Where should a
replication algorithm of this type be described? The DHT? The
storage layer? The usage?]]</t>
</note>
</section>
<section title="Joining">
<t>The join process for a joining party (JP) with peer-id n is as
follows.</t>
<list style="numbers">
<t>JP connects to its chosen bootstrap node.</t>
<t>JP uses a series of PINGs to populate its routing table.</t>
<t>JP sends CONNECT requests to initiate connections to each of the
peers in the connection table as well as to the desired finger table
entries. Note that this does not populate their routing tables, but
only their connection tables, so JP will not get messages that it is
expected to route to other nodes.</t>
<t>JP enters all the peers it contacted into its routing table.</t>
<t>JP sends a JOIN to its immediate successor, the admitting peer
(AP) for peer-id n. The AP sends the response to the JOIN.</t>
<t>AP does a series of STORE requests to JP to store the data that
JP will be responsible for.</t>
<t>AP sends JP an UPDATE explicitly labelling JP as its predecessor.
At this point, JP is part of the ring and responsible for a section
of the overlay. AP can now forget any data which is assigned to JP
and not AP.</t>
<t>AP sends an UPDATE to all of its neighbors with the new values of
its neighbor set (including JP).</t>
<t>JP sends UPDATES to all the peers in its routing table.</t>
</list>
<t>In order to populate its routing table, JP sends a PING via the
bootstrap node directed at resource-id n+1 (directly after its own
resource-id). This allows it to discover its own successor. Call that
node p0. It then sends a ping to p0+1 to discover its successor (p1).
This process can be repeated to discover as many successors as
desired. The values for the two peers before p will be found at a
later stage when n receives an UPDATE.</t>
<t>In order to set up its neighbor table entry for peer i, JP simply
sends a CONNECT to peer (n+2^(numBitsInPeerId-i). This will be routed
to a peer in approximately the right location around the ring.</t>
</section>
<section title="UPDATEs">
<t>An UPDATE is defined as</t>
<t>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
peer_id predecessors<255>;
peer_id successors<255>;
} chord_update;
]]></artwork>
</figure>
</t>
<!--
chord-update = uint8 ; number of predecessors
*peer-id ; predecessor set
uint8 ; number of successors
*peer-id ; successor set
-->
<t>The contents of this message are:</t>
<list style="hanging">
<t hangText="Predecessors -">The predecessor set of the UPDATEing
peer.</t>
<t hangText="Successors -">The successor set of the UPDATEing
peer.</t>
</list>
<t>A peer MUST maintain an association (via CONNECT) to every member
of its neighbor set. A peer MUST attempt to maintain at least three
predecessors and three successors. However, it MUST send its entire
set in any UPDATE message.</t>
<section title="Sending UPDATEs">
<t>Every time a connection to a peer in the neighborhood set is lost
(as determined by connectivity pings), the peer should remove the
entry from its neighborhood table and send an UPDATE to all the
remaining neighbors. The update will contain all the peer-ids of the
current entries of the table (after the failed one has been
removed).</t>
<t>If connectivity is lost to all three of the peers that succeed
this peer in the ring, then this peer should behave as if it is
joining the network and use PINGs to find a peer and send it a JOIN.
If connectivity is lost to all the peers in the finger table, this
peer should assume that it has been disconnected from the rest of
the network, and it should periodically try to join the DHT.</t>
</section>
<section title="Receiving UPDATEs">
<t>When a peer, N, receives an UPDATE request, it examines the
peer-ids in the UPDATE and at its neighborhood table and decides if
this UPDATE would change its neighborhood table. This is done by
taking the set of peers currently in the neighborhood table and
comparing them to the peers in the update request. There are three
major cases:</t>
<list style="symbols">
<t>The UPDATE contains peers that would not change the neighbor
set because they match the neighborhood table.</t>
<t>The UPDATE contains peers closer to N than those in its
neighborhood table.</t>
<t>The UPDATE defines peers that indicate a neighborhood table
further away from N than some of its neighborhood table. Note that
merely receiving peers further away does not demonstrate this,
since the update could be from a node far away from N. Rather, the
peers would need to bracket N.</t>
</list>
<t>In the first case, no change is needed.</t>
<t>In the second case, N MUST attempt to CONNECT to the new peers
and if it is successful it MUST adjust its neighbor set accordingly.
Note that it can maintain the now inferior peers as neighbors, but
it MUST remember the closer ones.</t>
<t>The third case implies that a neighbor has disappeared, most
likely because it has simply been disconnected but perhaps because
of overlay instability. N MUST PING the questionable peers to
discover if they are indeed missing and if so, remove them from its
neighborhood table.</t>
<t>After any PINGs and CONNECTs are done, if the neighborhood table
changes, the peer sends an UPDATE request to each of its neighbors
that was in either the old table or the new table. These UPDATEs are
what ends up filling in the predecessor/successor tables of peers
that this peer is a neighbor to. A peer MUST NOT enter itself in
its successor or predecessor table and instead should leave the
entries empty.</t>
<t>A peer N which is responsible for a resource-id R discovers that
the replica set for R (the next two nodes in its successor set) has
changed, it MUST send a STORE for any data associated with R to any
new node in the replica set. It SHOULD not delete data from peers
which have left the replica set.</t>
<t>When a peer N detects that it is no longer in the replica set for
a resource R (i.e., there are three predecessors between N and R),
it SHOULD delete all data associated with R from its local
store.</t>
</section>
<section title="Stabilization">
<t>A peer MUST periodically send an UPDATE to every peer in its
routing table. The purpose of this is to keep the predecessor and
successor lists up to date and to detect connection failures. The
default time is about every ten minutes, but the enrollment server
SHOULD set this in the configuration document using the
"chord-128-2-8-update-frequency" element (denominated in seconds.) A
peer SHOULD randomly offset these UPDATEs so they do not occur all
at once. If an UPDATE fails or times out, the peer MUST mark that
entry in the neighbor table invalid and attempt to reestablish a
connection. If no connection can be established, the peer MUST
attempt to establish a new peer as its neighbor and do whatever
replica set adjustments are required.</t>
<t>Periodically a peer should select a random entry i from the
finger table and do a PING to peer (n+2^(numBitsInPeerId-i). The
purpose of this is to find a more accurate finger table entry if
there is one. This is done less frequently than the connectivity
checks in the previous section because forming new connections is
somewhat expensive and the cost needs to be balanced against the
cost of not having the most optimal finger table entries. The
default time is about every hour, but the enrollment server SHOULD
set this in the configuration document using the
"chord-128-2-8-ping-frequency" element (denominated in seconds). If
this returns a different peer than the one currently in this entry
of the peer table, then a new connection should be formed to this
peer and it should replace the old peer in the finger table.</t>
</section>
</section>
<section title="Leaving">
<t>Peers SHOULD send a LEAVE request prior to exiting the DHT. Any
peer which receives a LEAVE for a peer n in its neighbor set must
remove it from the neighbor set, update its replica sets as
appropriate (including STOREs of data to new members of the replica
set) and send UPDATEs containing its new predecessor and successor
tables.</t>
</section>
</section>
<section anchor="secEnrollment" title="Enrollment and Bootstrap">
<section title="Discovery">
<t>When a peer first joins a new overlay, it starts with a discovery
process to find an enrollment server. Related work to the approach
used here is described in <xref
target="I-D.garcia-p2psip-dns-sd-bootstrapping"></xref> and <xref
target="I-D.matthews-p2psip-bootstrap-mechanisms"></xref>. The peer
first determines the overlay name. This value is provided by the user
or some other out of band provisioning mechanism. If the name is an IP
address, that is directly used otherwise the peer MUST do a DNS SRV
query using a Service name of "p2p_enroll" and a proto of tcp to find
an enrollment server.</t>
<t>If the overlay name ends in .local, then the DNS SRV lookup is done
using implement <xref target="I-D.cheshire-dnsext-dns-sd"></xref> with
a Service name of "p2p_menroll" can also be tried to find an
enrollment server. If they implement this, the user name can be used
as the Instance Identifier label.</t>
<t>Once an address for the enrollment servers is determined, the peer
forms an HTTPS connection to that IP address. The certificate MUST
match the overlay name as described in <xref target="RFC2818"></xref>.
The peer then performs a GET to the URL formed by appending a path of
"/p2psip/enroll" to the overlay name. For example, if the overlay name
was example.com, the URL would be
"https://example.com/p2psip/enroll".</t>
<t>The result is an XML configuration file with the syntax described
in the following section.</t>
</section>
<section anchor="sec-configuration" title="Overlay Configuration">
<t>This specification defines a new content type
"application/p2p-overlay+xml" for an MIME entity that contains overlay
information. An example document is shown below.</t>
<t>
<figure>
<artwork><![CDATA[
<?xml version="1.0" encoding="US-ASCII"?>
<overlay name="chord.example.com" expiration="86400">
<dht name="chord-128-2-8"/>
<root-cert>[DER here]</root-cert>
<required-usage name="SIP"/>
<credential-server url="https://www.example.com/csr"/>
<bootstrap-peer address="192.0.2.2" port="5678"/>
<bootstrap-peer address="192.0.2.3" port="5678"/>
<bootstrap-peer address="192.0.2.4" port="5678"/>
<multicast-bootstrap="192.0.2.99" port="5678"/>
</overlay>
]]></artwork>
</figure>
</t>
<t>The file MUST be a well formed XML document and it SHOULD contain
an encoding declaration in the XML declaration. If the charset
parameter of the MIME content type declaration is present and it is
different from the encoding declaration, the charset parameter takes
precedence. Every application conferment to this specification MUST
accept the UTF-8 character encoding to ensure the minimal
interoperability. The namespace for the elements defined in this
specification is urn:ietf:params:xml:ns:p2p:overlay.</t>
<t>The file can contain multiple "overlay" elements where each one
contains the configuration information for a different overlay. Each
"overlay" has the following attributes:</t>
<t>
<list style="hanging">
<t hangText="name:">name of the overlay</t>
<t hangText="expiration:">time in future at which this overlay
configuration is not longer valid and need to be retrieved again.
This is expressed in seconds from the current time.</t>
</list>
</t>
<t>Inside each overlay element, the following elements can occur:</t>
<list style="hanging">
<t hangText="dht -">This element has an attribute called name that
describes which dht algorithm is being used.</t>
<t hangText="root-cert -">This element contains a DER encoded
X.509v3 certificate that is the root trust store used to sign all
certificates in this overlay. There can be more than one of
these.</t>
<t hangText="required-usage -">This element has an attribute called
"name" that describes a usage that peers in this overlay are
required to support. More than one required-usage element may be
present.</t>
<t hangText="credential-server -">This element contains the URL at
which the credential server can be reached in a "url" element. This
URL MUST be of type "https:". More than one credential-server
element may be present.</t>
<t hangText="bootstrap-peer -">This elements represents the address
of one of the bootstrap peers. It has an attribute called "address"
that represents the IP address and an attribute called "port" that
represents the port. More than one bootstrap-peer element may be
present.</t>
<t hangText="multicast-bootstrap -">This element represents the
address of a multicast address and port that may be used for
bootstrap and that peers SHOULD listen on to enable bootstrap. It
has an attributed called "address" that represents the IP address
and an attribute called "port" that represents the port. More than
one "multicast-bootstrap" element may be present.</t>
</list>
<t>[[TODO: Do a RelaxNG grammar.]]</t>
</section>
<section title="Credentials">
<t>If a credential-server element is provided in the configuration
document, that means that credentials are required to use the DHT. A
peer which does not yet have credentials MUST contact the credential
server to acquire them.</t>
<t>In order to acquire credentials, the peer generates an asymmetric
key pair and then generates a "Simple Enrollment Request" (as defined
in <xref target="I-D.ietf-pkix-2797-bis"></xref>) and sends this over
HTTPS as defined in <xref target="I-D.ietf-pkix-cmc-trans"></xref> to
the URL in the credential-server element. The subjectAltName in the
request MUST contain the required user name(s).</t>
<t>The credential server MUST authenticate the request using HTTP
digest <xref target="RFC2617"></xref>. If the authentication succeeds
and the requested user name(s) is acceptable, the server and returns a
certificate. The SubjectAltName field in the certificate contains the
following values:</t>
<t><list style="symbols">
<t>One or more Peer-IDs which MUST be cryptographically random
<xref target="RFC4086"></xref>. These MUST be chosen by the
credential server in such a way that they are unpredictable to the
requesting user.</t>
<t>The names this user is allowed to use in the overlay</t>
</list></t>
<t>The certificate is returned in a "Simple Enrollment Response".</t>
<t>The client MUST check that the certificate returned was signed by
one of the certificates received in the "root-cert" list of the
overlay configuration data. The peer then reads the certificate to
find the Peer-IDs it can use.</t>
</section>
<section title="Locating a Peer">
<t>In order to join the overlay, the peer MUST contact a bootstrap
peer. If the peer has cached bootstrap peers it SHOULD contact them
first by sending a PING to the known peer address with the destination
peer-id set to that peer's peer-id.</t>
<t>If no cached peers are available, then the peer SHOULD send a PING
to the address and port found in the broadcast-peers element in the
configuration document. This MAY be a multicast or anycast address.
The PING should use the wildcard peer-id as the destination
peer-id.</t>
<t>The responder peer that receives the PING SHOULD check that the
overlay name is correct and that the requester peer sending the
request has appropriate credentials for the overlay before responding
to the PING even if the response is only an error.</t>
<t>When the requester peer finally does receive a response from some
responding peer, it can note the peer-id in the response and use this
peer-id to start sending requests to join the DHT as described in
<xref target="sec-join-leave-maint"></xref> and <xref
target="sec-dht-maint"></xref>.</t>
<t>After a peer has successfully joined the overlay network, it SHOULD
periodically look at any peers to which it has managed to form direct
connections. Some of these peers MAY be added to the cached-peers list
and used in future boots. Peers that are not directly connected MUST
not be cached. The RECOMMENDED number of peers to cache is 10.</t>
</section>
</section>
<section title="Usages ">
<section title="Generic Usage Requirements">
<t>A new usage MUST specify the following information:</t>
<list style="symbols">
<t>The type-ids which the usage defines and what each type
means.</t>
<t>The data model for the data being stored (single value, array,
dictionary, etc.) for each type-id</t>
<t>Access control rules for each type-id.</t>
<t>The minimum amounts of data of each type that a conformant
implementation MUST store.</t>
</list>
<t>While each type-id MUST define what data model is used for its
data, that does not mean that it must define new data models. Where
useful, type-ids SHOULD use the build-in data models. However, they
MAY define any new required data models. The intention is that the
basic data model set be sufficient for most applications/usages.</t>
<note title="Note:">
<t>New usages MAY (and where useful SHOULD) reuse existing type-ids.
New type-ids only need to be defined where different data is stored
or different behavior is required.</t>
</note>
</section>
<section title="SIP Usage">
<t>The SIP usage allows a RELOAD overlay to be used as a distributed
SIP registrar/proxy network. The basic function of the SIP usage is to
allow Alice to start with a SIP URI (e.g., "bob@dht.example.com") and
end up with a connection which Bob's SIP UA can use to pass SIP
messages back and forth to Alice's SIP UA. Provides the following
three functions:</t>
<t><list style="symbols">
<t>Mapping SIP URIs that are not GRUUs to the overlay peer
responsible for the SIP UA.</t>
<t>Mapping SIP GRUUs to the DHT peer responsible for the SIP
UA.</t>
<t>Forming a connection directly to a DHT peer that is used to
send SIP messages to the SIP UA.</t>
</list></t>
<t><xref target="sec-sip-usage"></xref> provides an overview of how
these fit together.</t>
<section title="SIP-REGISTRATION type">
<t>The first mapping is provided using the SIP-REGISTRATION
type:</t>
<t><list style="hanging">
<t hangText="Type IDs">The seed for the SIP-REGISTRATION type is
a URI, typically the AOR for the user. The data stored is a
sip-registration-data, which can contain either another URI or a
route-list to the peer which is acting for the user. [[TODO: we
want to somehow put caller-prefs in here along with the route
list, but I'm not sure how to do it yet.]]</t>
<t hangText="Data Model">The data model for the SIP-REGISTRATION
type is dictionary. The dictionary key is the peer-id of the
storing peer. This allows each peer (presumably corresponding to
a single device) to store a single route mapping.</t>
<t hangText="Access Control">If certificate-based access control
is being used, stored data of type SIP-REGISTRATION must be
signed by a certificate which (1) contains user name matching
the storing URI used as the seed for the resource-id and (2)
contains a peer-id matching the storing dictionary key.</t>
<t hangText="Data Sizes">Peers MUST be prepared to store
SIP-REGISTRATION values of up to 10K and must be prepared to
store up to 10 values for each user name.</t>
</list></t>
<t>The contents of the SIP-REGISTRATION type are</t>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
typedef string sip_registration_uri;
struct {
string contact_prefs;
peer_id route_list<65000>;
} sip_registration_route;
enum {sip_registration_uri_type(1), sip_registration_route_type(2)} sip_registration_type;
select {
case sip_registration_uri_type:
sip_registration_uri registration_uri;
case sip_registration_route_type:
sip_registration_route registration_route;
} sip_registration_data_;
public struct {
sip_registration_data_ registration_data;
} sip_registration;
]]></artwork>
</figure>
<t>A registration may contain either a URI (type code 0x01) or a
contact preferences structure and a route list (type code 0x01). The
leading byte indicates the type.</t>
</section>
<section title="GRUUs">
<t>GRUUs do not require storing data in the DHT. Rather, they are
constructed by embedding a base64-encoded route list in the gr URI
parameter of the GRUU. The base64 encoding is done with the alphabet
specified in table 1 of RFC 4648 with the exception that ~ is used
in place of =. An example GRUU is
"sip:alice@example.com;gr=MDEyMzQ1Njc4OTAxMjM0NTY3ODk~". When a peer
needs to route a message to a GRUU in the same P2P network, it
simply uses the route list and connects to that peer.</t>
<t>Anonymous GRUUs are done in roughly the same way but require
either that the enrollment server issue a different peer-id for each
anonymous GRUU required or that a route list be used that includes a
peer that compresses the route list to stop the peer-id from being
revealed.</t>
</section>
<section title="SIP Connect">
<t>Once the route list for a user has been identified, the calling
peer uses the CONNECT request to form a connection to the peer
identified by the route list. The CONNECT request MUST contain the
connect-application value of 5160 (SIP). If certificate-based
authentication is in use, the responding peer MUST present a
certificate with a peer-id matching the terminal entry in the route
list.</t>
<t>[[TODO: Note that this constrains route lists from hiding the
last peer-id when used here. I think that's OK, but we should take a
look]]</t>
<t>Once the association has been formed, the calling peer sends
generic SIP messages down the new association and ordinary SIP
procedures are followed.</t>
</section>
<section title="SIP Tunnel">
<t>This usage allows two peers to exchange SIP messages across the
overlay using the TUNNEL method. TUNNEL is provided as an
alternative to using CONNECT because it allows a SIP message to be
sent immediately, without the delay associated with CONNECT. For a
simple SIP exchange, it may result in fewer messages being sent, as
well.</t>
<t>An implementation MUST use CONNECT for a dialog that is expected
to endure for sufficient time and exchange significant numbers of
messages. An implementation MAY establish an initial dialog using
TUNNELing and then migrate it to a direct dialog opened with CONNECT
once that negotiation is complete.</t>
<t>As an application of TUNNEL, this usage defines the following
items: <list style="symbols">
<t>For SIP, the application attribute is 5060.</t>
<t>The application MAY establish any dialog using TUNNEL if it
expects to replace it once a CONNECT request completes. The
application SHOULD NOT exchange messages with another SIP UA
repeatedly using a TUNNEL unless it is unable to complete a
CONNECT.</t>
<t>The Replaces header should be used to migrate dialogs
established via TUNNEL to a direct connection.</t>
<t>The dialogid is the GRUU of the destination of the
request.</t>
<t>By using the GRUU of the destination as the dialogid, the
receiving peer is able to deliver the message to the appropriate
process without parsing the SIP message.</t>
</list></t>
<t>In constructing the message, the SIP UA forms the message as if
it were being routed directly to the GRUU of the destination. The
SIP stack hands the message to RELOAD for delivery. Although the
message is passed through a sequence of untrusted peers, it is not
subject to modification by those peers because of the message's
signature.</t>
<t>OPEN ISSUE: should specify how to request encryption of the
message end-to-end.</t>
<note title="Note:">
<t>The easiest implementation of TUNNEL is likely to default to
sending all messages across a TUNNEL when the first message is
sent to a new destination GRUU and simultaneously issuing a
CONNECT. Messages then continue through the TUNNEL until the
CONNECT completes, at which point they are delivered via the new
connection.</t>
</note>
<t>OPEN ISSUE: If the tunneling vs direct decision can be made
equivalently to a link-layer decision, it may not be necessary to
modify the dialog or inform the SIP UA in any way that it has now
obtained a direct route.</t>
</section>
</section>
<section anchor="sec-stun-turn-usage" title="TURN Usage">
<t>When a node starts up, it joins the overlay network and forms
several connection in the process. If the ICE stage in any of these
connection return a reflexive address that is not the same as the
peers perceived address, then the peers is behind a NAT and not an
candidate for a TURN server. Additionally, if the peers IP address is
in the private address space range, then it is not a candidate for a
TURN server. Otherwise, the peer SHOULD assume it is a potential TURN
server and follow the procedures below.</t>
<t>If the node is a candidate for a TURN server it will insert some
pointers in the overlay so that other peers can find it. The overlay
configuration file specifies a turnDensity parameter that indicates
how many times each TURN server should record itself in the overlay.
Typically this should be set to the reciprocal of the estimate of what
percentage of peers will act as TURN servers. For each value, called
d, between 1 and turnDensity, the peer forms a seed by concatenating
its peer-ID and the value d. This seed is hashed to form a
Resource-ID. The address of the peer is stored at that Resource-ID
using type TURN-SERVICE and the turn-server production:</t>
<note title="Note:">
<t>Correct functioning of this algorithm depends critically on
having turnDensity be an accurate estimate of the true density of
TURN servers. If turnDensity is too high, then the process of
finding TURN servers becomes extremely expensive as multiple
candidate resource-ids must be probed.</t>
</note>
<t>Peers peers that provide the STUN-Relay server type need to support
the TURN extensions to STUN for media relay of both UDP and TCP
traffic as defined in <xref target="I-D.ietf-behave-turn" /> and [Add
REF for TURN-TCP].</t>
<figure>
<!--begin-pdu-->
<artwork><![CDATA[
public struct {
uint8 iteration;
ip_address_and_port address;
} turn_server;
]]></artwork>
<t>[[OPEN ISSUE: This structure only works for TURN servers that
have public addresses. It may be possible to use TURN servers that
are behind well-behaved NATs by first ICE connecting to them. If we
decide we want to enable that, this structure will need to change to
either be a peer-id or include that as an option.]]</t>
<!--
turn-server = ip-address-and-port
ip-address-and-port = ip-address
ip-port
ip-address = ip-address-type
ip4-address / ip6-address
ip-address-type = ip4-address-type / ip6-address-type ; uint8
ip4-address-type = 0x01
ip6-address-type = 0x02
ip4-address = uint32
ip6-address = uint128
ip-port = uint16
iteration = uint8
-->
</figure>
<t>
<list style="hanging">
<t hangText="Type IDs">This usage defines the TURN-SERVICE type-id
to indicate that a peer is willing to act as a TURN server. The
FIND command MUST return results for the TURN-SERVICE type-id.</t>
<t hangText="Data Model">The TURN-SERVICE stores a single value
for each resource-id.</t>
<t hangText="Access Control">If certificate-based access control
is being used, stored data of type TURN-SERVICE MUST be
authenticated by a certificate which contains a peer-id which when
hashed with the iteration counter produces the resource-id being
stored at.</t>
<t hangText="Data Sizes">TURN-SERVICE values are of fixed size.
Peers MUST be prepared to store values with iteration counter of
up to 100.</t>
</list>
</t>
<t>The data is stored in a data structure with the IP address of the
server and an indication whether the address is an IPv4 or IPv6
address. The seed used to form the storage Resource-ID is simply the
peer-id. The access control rule is that the certificate used to sign
the request must contain a peer-id that when hashed would match the
Resource-ID where the data is being stored.</t>
<t>Peers can find other servers by selecting a random Resource-ID and
then doing a FIND request for the appropriate server type with that
Resource-ID. The FIND request gets routed to a random peer based on
the Resource-ID. If that peer knows of any servers, they will be
returned. The returned response may be empty if the peer does not know
of any servers, in which case the process gets repeated with some
other random Resource-ID. As long as the ratio of servers relative to
peers is not too low, this approach will result in finding a server
relatively quickly.</t>
<t>Open issues: Should there be low and high bandwidth version of
STUN-Relay one can find? Low would be usable for signaling type things
and high would be usable for audio, video, and others.</t>
</section>
<section title="Certificate Store Usages">
<t>The Certificate Store usage allows a peer to store its certificate
in the overlay, thus avoiding the need to send a certificate in each
message - a reference may be sent instead.</t>
<t>A user/peer SHOULD store its certificate at resource-ids derived
from two seeds:</t>
<t><list style="symbols">
<t>The user names in the certificate.</t>
<t>The peer-ids in the certificate.</t>
</list></t>
<t>Note that in the second case the certificate is not stored at the
peer's peer-id but rather at a hash of the peer's peer-id. The
intention here (as is common throughout RELOAD) is to avoid making a
peer responsible for its own data.</t>
<t>A peer should ensure that the user's certificates are stored in the
DHT when joining and redo the check about every 24 hours after that.
Certificate data should be stored with an expiry time of 60 days. When
a client is checking the existence of data, if the expiry is less than
30 days, it should be refreshed to have an expiry of 60 days. The
certificate information is frequently used for many operations, and
peers should cache it for 8 hours.</t>
<t><list style="hanging">
<t hangText="Type IDs">This usage defines the CERTIFICATE type-id
to store a peer or user's certificate.</t>
<t hangText="Data Model">The data model for CERTIFICATE data is of
type array.</t>
<t hangText="Access Control">The CERTIFICATE MUST contain a
peer-id or user name which, when hashed, maps the resource-id at
which the value is being stored.</t>
<t hangText="Data Sizes">Peers MUST be prepared to store at least
10 certificates of sizes up to 1K each.</t>
</list></t>
</section>
</section>
<section title="Security Considerations">
<section title="Overview">
<t>RELOAD provides a somewhat generic DHT storage service, albeit one
designed to be useful for P2P SIP. In this section we discuss security
issues that are likely to be relevant to any usage of RELOAD. In the
subsequent section we describe issues that are specific to SIP.</t>
<t>In any DHT, any given user depends on a number of peers with which
they have no well-defined relationship except that they are fellow
members of the DHT. In practice, these other nodes may be friendly,
lazy, curious, or outright malicious. No security system can provide
complete protection in an environment where most nodes are malicious.
The goal of security in RELOAD is to provide strong security
guarantees of some properties even in the face of a large number of
malicious nodes and to allow the DHT to function correctly in the face
of a modest number of malicious nodes.</t>
<t>P2PSIP deployments require the ability to authenticate both peers
and resources (users) without the active presence of a trusted entity
in the system. We describe two mechanisms. The first mechanism is
based on public key certificates and is suitable for general
deployments. The second is based on an overlay-wide shared symmetric
key and is suitable only for limited deployments in which the
relationship between admitted peers is not adversarial.</t>
</section>
<section title="Attacks on P2P Overlays">
<t>The two basic functions provided by DHT nodes are storage and
routing: some node is responsible for storing your data and for
allowing you to fetch data from others. Some other set of nodes are
responsible for routing messages to and from the storing nodes. Each
of these issues is covered in the following sections.</t>
<t>P2P overlays are subject to attacks by subversive nodes that may
attempt to disrupt routing, corrupt or remove user registrations, or
eavesdrop on signaling. The certificate-based security algorithms we
describe in this draft are intended to protect DHT routing and user
registration information in RELOAD messages.</t>
<t>To protect the signaling, the first requirement is to ensure that
all messages are received from authorized members of the overlay. For
this reason, RELOAD transports all messages over DTLS or TLS, which
provides message integrity and authentication of the directly
communicating peer. In addition, when the certificate-based security
system is used, messages and data are digitally signed with the
sender's private key, providing end-to-end security for
communications.</t>
<t>In order to protect data storage, in the certificate-based security
scheme, all stored data is signed by the owner of the data. This
allows the storing peer to verify that the storer is authorized to
perform a store at that resource-id and also allows any consumer of
the data to verify the provenance and integrity of the data when it
retrieves it.</t>
</section>
<section title="Certificate-based Security">
<t>This specification stores users' registrations and possibly other
data in a Distributed Hash table (DHT). This requires a solution to
securing this data as well as securing, as well as possible, the
routing in the DHT. Both types of security are based on requiring that
every entity in the system (whether user or peer) authenticate
cryptographically using an asymmetric key pair tied to a
certificate.</t>
<t>When a user enrolls in the DHT, they request or are assigned a
unique name, such as "alice@dht.example.net". These names are unique
and are meant to be chosen and used by humans much like a SIP Address
of Record (AOR) or an email address. The user is also assigned one or
more peer-IDs by the central enrollment authority. Both the name and
the peer ID are placed in the certificate, along with the user's
public key.</t>
<t>Each certificate enables an entity to act in two sorts of
roles:</t>
<t><list>
<t>As a user, storing data at specific Resource-IDs in the DHT
corresponding to the user name.</t>
<t>As a DHT peer with the peer ID(s) listed in the
certificate.</t>
</list></t>
<t>Note that since only users of this DHT need to validate a
certificate, this usage does not require a global PKI. It does,
however, require a central enrollment authority which acts as the
certificate authority for the DHT. This authority signs each peer's
certificate. Because each peer possesses the CA's certificate (which
they receive on enrollment) they can verify the certificates of the
other entities in the overlay without further communication. Because
the certificates contain the user/peer's public key, communications
from the user/peer can be verified in turn.</t>
<t>All implementations MUST implement certificate-based security.</t>
</section>
<section title="Shared-Secret Security">
<t>For small environments where deployment of the PKI necessary to use
a certificate-based model is impractical, RELOAD supports a shared
secret security that relies on a single key that is shared among all
members of the overlay. It is appropriate for small groups that wish
to form a private network without complexity. In shared secret mode,
all the peers share a single symmetric key which is used to key
TLS-PSK <xref target="RFC4279"></xref> or TLS-SRP <xref
target="I-D.ietf-tls-srp"></xref> mode. A peer which does not know the
key cannot form TLS connections with any other peer and therefore
cannot join the overlay.</t>
<t>The shared-secret scheme prohibits unauthorized peers from joining
the overlay, but it provides no protection from a compromised peer
inserting arbitrary resource registrations, performing a Sybil
attack<xref target="Sybil"></xref>, or performing other attacks on the
resources or routing. Thus, it is only safe to use in limited settings
in which peers are not adversarial. In addition, because the messages
and data are not authenticated, each intermediate peer MUST take care
to use TLS and check the other peer's knowledge of the shared secret,
or message insertion is possible.</t>
<t>If the shared secret key for the shared-key security scheme is
discovered by an attacker, then most of the security of the scheme is
lost: an attacker can impersonate any peer to any other peer. Thus,
the shared-secret scheme is only appropriate for small deployments,
such as a small office or ad hoc overlay set up among participants in
a meeting.</t>
<t>One natural approach to a shared-secret scheme is to use a
user-entered password as the key. The difficulty with this is that in
TLS-PSK mode, such keys are highly subject to dictionary attacks. If
passwords are used as the source of shared-keys, then TLS-SRP is a
superior choice because it is not subject to dictionary attacks.</t>
</section>
<section title="Storage Security">
<t>When certificate-based security is used in RELOAD, any given
Resource-ID/type code pair (a slot) is deterministically bound to some
small set of certificates. In order to write data in a slot, the
writer must prove possession of the private key for one of those
certificates. Moreover, all data is stored signed by the certificate
which authorized its storage. This set of rules makes questions of
authorization and data integrity - which have historically been thorny
for DHTs - relatively simple.</t>
<t>When shared-secret security is used, then all peers trust all other
peers, provided that they have demonstrated that they have the
credentials to join the overlay at all. The following text therefore
applies only to certificate-based security.</t>
<section title="Authorization">
<t>When a client wants to store some value in a slot, it first
digitally signs the value with its own private key. It then sends a
STORE request that contains both the value and the signature towards
the storing peer (which is defined by the seed construction
algorithm for that particular type of value).</t>
<t>When the storing peer receives the request, it must determine
whether the storing client is authorized to store in this slot. In
order to do so, it executes the seed construction algorithm for the
specified type based on the user's certificate information. It then
computes the Resource-ID from the seed and verifies that it matches
the slot which the user is requesting to write to. If it does, the
user is authorized to write to this slot, pending quota checks as
described in the next section.</t>
<t>For example, consider the certificate with the following
properties:</t>
<figure>
<artwork><![CDATA[
User name: alice@dht.example.com
Peer-Id: 013456789abcdef
Serial: 1234
]]></artwork>
</figure>
<t>If Alice wishes to STORE a value of the "SIP Location" type, the
seed will be the SIP AOR "sip:alice@dht.example.com". The
Resource-ID will be determined by hashing the seed. When a peer
receives a request to store a record at Resource-ID X, it takes the
signing certificate and recomputes the seed, in this case
"alice@dht.example.com". If H("alice@dht.example.com")=X then the
STORE is authorized. Otherwise it is not. Note that the seed
construction algorithm may be different for other types.</t>
</section>
<section title="Distributed Quota">
<t>Being a peer in a DHT carries with it the responsibility to store
data for a given region of the DHT. However, if clients were allowed
to store unlimited amounts of data, this would create unacceptable
burdens on peers, as well as enabling trivial denial of service
attacks. RELOAD addresses this issue by requiring each usage to
define maximum sizes for each type of stored data. Attempts to store
values exceeding this size SHOULD be rejected. Because each slot is
bound to a small set of certificates, these size restrictions also
create a distributed quota mechanism, with the quotas administered
by the central enrollment server.</t>
<t>Allowing different types of data to have different size
restrictions allows new usages the flexibility to define limits that
fit their needs without requiring all usages to have expansive
limits. Because peers know at joining time what usages they must
support (see <xref target="sec-configuration"></xref>), peers can to
some extent predict their storage requirements.</t>
</section>
<section title="Correctness">
<t>Because each stored value is signed, it is trivial for any
retrieving peer to verify the integrity of the stored value. Some
more care needs to be taken to prevent version rollback attacks.
Rollback attacks on storage are prevented by the use of store times
and lifetime values in each store. A lifetime represents the latest
time at which the data is valid and thus limits (though does not
completely prevent) the ability of the storing node to perform a
rollback attack on retrievers. In order to prevent a rollback attack
at the time of the STORE request, we require that storage times be
monotonically increasing. Storing peers MUST reject STORE requests
with storage times smaller than or equal to those they are currently
storing. In addition, a fetching node which receives a data value
with a storage time older than the result of the previous fetch
knows a rollback has occurred.</t>
</section>
<section title="Residual Attacks">
<t>The mechanisms described here provide a high degree of security,
but some attacks remain possible. Most simply, it is possible for
storing nodes to refuse to store a value (reject any request). In
addition, a storing node can deny knowledge of values which it
previously accepted. To some extent these attacks can be ameliorated
by attempting to store to/retrieve from replicas, but a retrieving
client has trouble knowing whether it should try this or not (since
there is a cost to doing so.)</t>
<t>Although the certificate-based authentication scheme compromising
a single peer from being able to forge data owned by other peers.
Furthermore, although a subversive peer can refuse to return data
resources for which it is responsible it cannot return forged data
because it cannot provide authentication for such registrations.
Therefore parallel searches for redundant registrations can mitigate
most of the affects of a compromised peer. The ultimate reliability
of such an overlay is a statistical question based on the
replication factor and the percentage of compromised peers.</t>
<t>In addition, when a type is multivalued (e.g., an array), the
storing node can return only some subset of the values, thus biasing
its responses. This can be countered by using single values rather
than sets, but that makes coordination between multiple storing
agents much more difficult. This is a tradeoff that must be made
when designing any usage.</t>
</section>
</section>
<section title="Routing Security">
<t>Because the storage security system guarantees (within limits) the
integrity of the stored data, routing security focuses on stopping the
attacker from performing a DOS attack on the system by mis-routing
requests in the DHT. There are a few obvious observations to make
about this. First, it is easy to ensure that an attacker is at least a
valid peer in the DHT. Second, this is a DOS attack only. Third, if a
large percentage of the peers on the DHT are controlled by the
attacker, it is probably impossible to perfectly secure against
this.</t>
<section title="Background">
<t>In general, attacks on DHT routing are mounted by the attacker
arranging to route traffic through or two nodes it controls. In the
Eclipse attack <xref target="Eclipse"></xref> the attacker tampers
with messages to and from nodes for which it is on-path with respect
to a given victim node. This allows it to pretend to be all the
nodes that are reachable through it. In the Sybil attack <xref
target="Sybil"></xref>, the attacker registers a large number of
nodes and is therefore able to capture a large amount of the traffic
through the DHT.</t>
<t>Both the Eclipse and Sybil attacks require the attacker to be
able to exercise control over her peer IDs. The Sybil attack
requires the creation of a large number of peers. The Eclipse attack
requires that the attacker be able to impersonate specific peers. In
both cases, these attacks are limited by the use of centralized,
certificate-based admission control.</t>
</section>
<section title="Admissions Control">
<t>Admission to an RELOAD DHT is controlled by requiring that each
peer have a certificate containing its peer ID. The requirement to
have a certificate is enforced by using TLS mutual authentication on
each connection. Thus, whenever a peer connects to another peer,
each side automatically checks that the other has a suitable
certificate. These peer IDs are randomly assigned by the central
enrollment server. This has two benefits:</t>
<t><list style="symbols">
<t>It allows the enrollment server to limit the number of peer
IDs issued to any individual user.</t>
<t>It prevents the attacker from choosing specific peer IDs.</t>
</list></t>
<t>The first property allows protection against Sybil attacks
(provided the enrollment server uses strict rate limiting policies).
The second property deters but does not completely prevent Eclipse
attacks. Because an Eclipse attacker must impersonate peers on the
other side of the attacker, he must have a certificate for suitable
peer IDs, which requires him to repeatedly query the enrollment
server for new certificates which only will match by chance. From
the attacker's perspective, the difficulty is that if he only has a
small number of certificates the region of the DHT he is
impersonating appears to be very sparsely populated by comparison to
the victim's local region.</t>
</section>
<section title="Peer Identification and Authentication">
<t>In general, whenever a peer engages in DHT activity that might
affect the routing table it must establish its identity. This
happens in two ways. First, whenever a peer establishes a direct
connection to another peer it authenticates via TLS mutual
authentication. All messages between peers are sent over this
protected channel and therefore the peers can verify the data origin
of the last hop peer for requests and responses without further
cryptography.</t>
<t>In some situations, however, it is desirable to be able to
establish the identity of a peer with whom one is not directly
connected. The most natural case is when a peer UPDATEs its state.
At this point, other peers may need to update their view of the DHT
structure, but they need to verify that the UPDATE message came from
the actual peer rather than from an attacker. To prevent this, all
DHT routing messages are signed by the peer that generated them.</t>
<t>[TODO: this allows for replay attacks on requests. There are two
basic defenses here. The first is global clocks and loose
anti-replay. The second is to refuse to take any action unless you
verify the data with the relevant node. This issue is
undecided.]</t>
<t>[TODO: I think we are probably going to end up with generic
signatures or at least optional signatures on all DHT messages.]</t>
</section>
<section title="Protecting the Signaling">
<t>The goal here is to stop an attacker from knowing who is
signaling what to whom. An attacker being able to observe the
activities of a specific individual is unlikely given the
randomization of IDs and routing based on the present peers
discussed above. Furthermore, because messages can be routed using
only the header information, the actual body of the RELOAD message
can be encrypted during transmission.</t>
<t>There are two lines of defense here. The first is the use of TLS
or DTLS for each communications link between peers. This provides
protection against attackers who are not members of the overlay. The
second line of defense, if certificate-based security is used, is to
digitally sign each message. This prevents adversarial peers from
modifying messages in flight, even if they are on the routing
path.</t>
</section>
<section title="Residual Attacks">
<t>The routing security mechanisms in RELOAD are designed to contain
rather than eliminate attacks on routing. It is still possible for
an attacker to mount a variety of attacks. In particular, if an
attacker is able to take up a position on the DHT routing between A
and B it can make it appear as if B does not exist or is
disconnected. It can also advertise false network metrics in attempt
to reroute traffic. However, these are primarily DoS attacks.</t>
<t>The certificate-based security scheme secures the namespace, but
if an individual peer is compromised or if an attacker obtains a
certificate from the CA, then a number of subversive peers can still
appear in the overlay. While these peers cannot falsify responses to
resource queries, they can respond with 404 error messages,
effecting a DoS attack on the resource registration. They can also
subvert routing to other compromised peers. To defend against such
attacks, a resource search must still consist of parallel searches
for replicated registrations.</t>
</section>
</section>
<section title="SIP-Specific Issues">
<section title="Fork Explosion">
<t>Because SIP includes a forking capability (the ability to
retarget to multiple recipients), fork bombs are a potential DoS
concern. However, in the SIP usage of RELOAD, fork bombs are a much
lower concern because the calling party is involved in each
retargeting event and can therefore directly measure the number of
forks and throttle at some reasonable number.</t>
</section>
<section title="Malicious Retargeting">
<t>Another potential DoS attack is for the owner of an attractive
number to retarget all calls to some victim. This attack is
difficult to ameliorate without requiring the target of a SIP
registration to authorize all stores. The overhead of that
requirement would be excessive and in addition there are good use
cases for ratargeting to a peer without there explicit
cooperation.</t>
</section>
<section title="Privacy Issues">
<t>All RELOAD SIP registration data is public. Methods of providing
location and identity privacy are still being studied.</t>
</section>
</section>
</section>
<!--
<section title="Operations and Management Considerations"></section>
<section title="IANA Considerations">
<section title="DHT Types"></section>
<section title="Stored Data Types"></section>
<section title="Request & Responses Types"></section>
<section title="Parameter Types">
<t></t>
</section>
<t>TODO - add IANA registration for p2p_enroll SRV</t>
</section>
-->
<section title="Examples">
<t>See draft [TODO add ref] for message flow examples.</t>
</section>
<section title="Acknowledgments">
<t>This draft is a merge of the "REsource LOcation And Discovery
(RELOAD)" draft by David A. Bryan, Marcia Zangrilli and Bruce B.
Lowekamp, the "Address Settlement by Peer to Peer" draft by Cullen
Jennings, Jonathan Rosenberg, and Eric Rescorla, the "Security
Extensions for RELOAD" draft by Bruce B. Lowekamp and James Deverick,
and the "A Chord-based DHT for Resource Lookup in P2PSIP" by Marcia
Zangrilli and David A. Bryan.</t>
</section>
<section title="Appendix: Operation with SIP clients outside the DHT domain"></section>
<section title="Appendix: Notes on DHT Algorithm Selection">
<t>An important point: if you assume NATs are doing ICE to set up
connections, you want a lot fewer connections than you might have on a
very open network - this might push towards something like Chord with
fewer connections than, say, bamboo.</t>
<t>TODO - ref draft-irtf-p2prg-survey-search</t>
</section>
</middle>
<back>
<references title="Normative References">
<reference anchor="RFC2119">
<front>
<title abbrev="RFC Key Words">Key words for use in RFCs to Indicate
Requirement Levels</title>
<author fullname="Scott Bradner" initials="S." surname="Bradner">
<organization>Harvard University</organization>
<address>
<postal>
<street>1350 Mass. Ave.</street>
<street>Cambridge</street>
<street>MA 02138</street>
</postal>
<phone>- +1 617 495 3864</phone>
<email>sob@harvard.edu</email>
</address>
</author>
<date month="March" year="1997" />
<area>General</area>
<keyword>keyword</keyword>
</front>
<seriesInfo name="BCP" value="14" />
<seriesInfo name="RFC" value="2119" />
<format octets="4723" target="ftp://ftp.isi.edu/in-notes/rfc2119.txt"
type="TXT" />
<format octets="15905"
target="http://xml.resource.org/public/rfc/html/rfc2119.html"
type="HTML" />
<format octets="5661"
target="http://xml.resource.org/public/rfc/xml/rfc2119.xml"
type="XML" />
</reference>
<reference anchor="I-D.ietf-mmusic-ice">
<front>
<title>Interactive Connectivity Establishment (ICE): A Protocol for
Network Address Translator (NAT) Traversal for Offer/Answer
Protocols</title>
<author fullname="Jonathan Rosenberg" initials="J"
surname="Rosenberg">
<organization></organization>
</author>
<date day="12" month="June" year="2007" />
<abstract>
<t>This document describes a protocol for Network Address
Translator (NAT) traversal for multimedia sessions established
with the offer/ answer model. This protocol is called Interactive
Connectivity Establishment (ICE). ICE makes use of the Session
Traversal Utilities for NAT (STUN) protocol, applying its binding
discovery and relay usages, in addition to defining a new usage
for checking connectivity between peers. ICE can be used by any
protocol utilizing the offer/answer model, such as the Session
Initiation Protocol (SIP).</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-mmusic-ice-16" />
<format target="http://www.ietf.org/internet-drafts/draft-ietf-mmusic-ice-16.txt"
type="TXT" />
</reference>
<reference anchor="I-D.ietf-behave-rfc3489bis">
<front>
<title>Session Traversal Utilities for (NAT) (STUN)</title>
<author fullname="Jonathan Rosenberg" initials="J"
surname="Rosenberg">
<organization></organization>
</author>
<date day="8" month="March" year="2007" />
<abstract>
<t>Session Traversal Utilities for NAT (STUN) is a lightweight
protocol that serves as a tool for application protocols in
dealing with NAT traversal. It allows a client to determine the IP
address and port allocated to them by a NAT and to keep NAT
bindings open. It can also serve as a check for connectivity
between a client and a server in the presence of NAT, and for the
client to detect failure of the server. STUN works with many
existing NATs, and does not require any special behavior from
them. As a result, it allows a wide variety of applications to
work through existing NAT infrastructure.</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft"
value="draft-ietf-behave-rfc3489bis-06" />
<format target="http://www.ietf.org/internet-drafts/draft-ietf-behave-rfc3489bis-06.txt"
type="TXT" />
</reference>
<reference anchor="I-D.ietf-behave-turn">
<front>
<title>Obtaining Relay Addresses from Simple Traversal Underneath
NAT (STUN)</title>
<author fullname="Jonathan Rosenberg" initials="J"
surname="Rosenberg">
<organization></organization>
</author>
<date day="7" month="March" year="2007" />
<abstract>
<t>This specification defines a usage of the Simple Traversal
Underneath NAT (STUN) Protocol for asking the STUN server to relay
packets towards a client. This usage is useful for elements behind
NATs whose mapping behavior is address and port dependent. The
extension purposefully restricts the ways in which the relayed
address can be used. In particular, it prevents users from running
general purpose servers from ports obtained from the STUN
server.</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-behave-turn-03" />
<format target="http://www.ietf.org/internet-drafts/draft-ietf-behave-turn-03.txt"
type="TXT" />
</reference>
<reference anchor="I-D.ietf-pkix-cmc-trans">
<front>
<title>Certificate Management over CMS (CMC) Transport
Protocols</title>
<author fullname="Jim Schaad" initials="J" surname="Schaad">
<organization></organization>
</author>
<author fullname="Michael Myers" initials="M" surname="Myers">
<organization></organization>
</author>
<date day="16" month="May" year="2006" />
<abstract>
<t>This document defines a number of transport mechanisms that are
used to move CMC (Certificate Management over CMS (Cryptographic
Message Syntax)) messages. The transport mechanisms described in
this document are: HTTP, file, mail and TCP.</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-pkix-cmc-trans-05" />
<format target="http://www.ietf.org/internet-drafts/draft-ietf-pkix-cmc-trans-05.txt"
type="TXT" />
</reference>
<reference anchor="I-D.ietf-pkix-2797-bis">
<front>
<title>Certificate Management Messages over CMS</title>
<author fullname="Michael Myers" initials="M" surname="Myers">
<organization></organization>
</author>
<author fullname="Jim Schaad" initials="J" surname="Schaad">
<organization></organization>
</author>
<date day="3" month="March" year="2006" />
<abstract>
<t>This document defines the base syntax for CMC, a Certificate
Management protocol using CMS (Cryptographic Message Syntax). This
protocol addresses two immediate needs within the Internet PKI
community: 1. The need for an interface to public key
certification products and services based on CMS and PKCS #10
(Public Key Cryptography 2. The need in S/MIME (Secure MIME) for a
certificate enrollment protocol for DSA-signed certificates with
Diffie-Hellman public keys. CMC also requires the use of the
transport document and the requirements usage document along with
this document for a full definition.</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-pkix-2797-bis-04" />
<format target="http://www.ietf.org/internet-drafts/draft-ietf-pkix-2797-bis-04.txt"
type="TXT" />
</reference>
<reference anchor="RFC4279">
<front>
<title>Pre-Shared Key Ciphersuites for Transport Layer Security
(TLS)</title>
<author fullname="P. Eronen" initials="P." surname="Eronen">
<organization></organization>
</author>
<author fullname="H. Tschofenig" initials="H." surname="Tschofenig">
<organization></organization>
</author>
<date month="December" year="2005" />
<abstract>
<t>This document specifies three sets of new ciphersuites for the
Transport Layer Security (TLS) protocol to support authentication
based on pre-shared keys (PSKs). These pre-shared keys are
symmetric keys, shared in advance among the communicating parties.
The first set of ciphersuites uses only symmetric key operations
for authentication. The second set uses a Diffie-Hellman exchange
authenticated with a pre-shared key, and the third set combines
public key authentication of the server with pre-shared key
authentication of the client. [STANDARDS TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="4279" />
<format octets="32160" target="ftp://ftp.isi.edu/in-notes/rfc4279.txt"
type="TXT" />
</reference>
<reference anchor="I-D.ietf-tls-srp">
<front>
<title>Using SRP for TLS Authentication</title>
<author fullname="Dave Taylor" initials="D" surname="Taylor">
<organization></organization>
</author>
<date day="14" month="June" year="2007" />
<abstract>
<t>This memo presents a technique for using the Secure Remote
Password protocol as an authentication method for the Transport
Layer Security protocol.</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-tls-srp-14" />
<format target="http://www.ietf.org/internet-drafts/draft-ietf-tls-srp-14.txt"
type="TXT" />
</reference>
<reference anchor="I-D.ietf-mmusic-ice-tcp">
<front>
<title>TCP Candidates with Interactive Connectivity Establishment
(ICE</title>
<author fullname="Jonathan Rosenberg" initials="J"
surname="Rosenberg">
<organization></organization>
</author>
<date day="8" month="March" year="2007" />
<abstract>
<t>Interactive Connectivity Establishment (ICE) defines a
mechanism for NAT traversal for multimedia communication protocols
based on the offer/answer model of session negotiation. ICE works
by providing a set of candidate transport addresses for each media
stream, which are then validated with peer-to-peer connectivity
checks based on Simple Traversal of UDP over NAT (STUN). ICE
provides a general framework for describing alternates, but only
defines UDP-based transport protocols. This specification extends
ICE to TCP-based media, including the ability to offer a mix of
TCP and UDP-based candidates for a single stream.</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft" value="draft-ietf-mmusic-ice-tcp-03" />
<format target="http://www.ietf.org/internet-drafts/draft-ietf-mmusic-ice-tcp-03.txt"
type="TXT" />
</reference>
<reference anchor="RFC3261">
<front>
<title>SIP: Session Initiation Protocol</title>
<author fullname="J. Rosenberg" initials="J." surname="Rosenberg">
<organization></organization>
</author>
<author fullname="H. Schulzrinne" initials="H."
surname="Schulzrinne">
<organization></organization>
</author>
<author fullname="G. Camarillo" initials="G." surname="Camarillo">
<organization></organization>
</author>
<author fullname="A. Johnston" initials="A." surname="Johnston">
<organization></organization>
</author>
<author fullname="J. Peterson" initials="J." surname="Peterson">
<organization></organization>
</author>
<author fullname="R. Sparks" initials="R." surname="Sparks">
<organization></organization>
</author>
<author fullname="M. Handley" initials="M." surname="Handley">
<organization></organization>
</author>
<author fullname="E. Schooler" initials="E." surname="Schooler">
<organization></organization>
</author>
<date month="June" year="2002" />
</front>
<seriesInfo name="RFC" value="3261" />
<format octets="647976"
target="ftp://ftp.isi.edu/in-notes/rfc3261.txt" type="TXT" />
</reference>
<reference anchor="RFC3263">
<front>
<title>Session Initiation Protocol (SIP): Locating SIP
Servers</title>
<author fullname="J. Rosenberg" initials="J." surname="Rosenberg">
<organization></organization>
</author>
<author fullname="H. Schulzrinne" initials="H."
surname="Schulzrinne">
<organization></organization>
</author>
<date month="June" year="2002" />
<abstract>
<t>The Session Initiation Protocol (SIP) uses DNS procedures to
allow a client to resolve a SIP Uniform Resource Identifier (URI)
into the IP address, port, and transport protocol of the next hop
to contact. It also uses DNS to allow a server to send a response
to a backup client if the primary client has failed. This document
describes those DNS procedures in detail. [STANDARDS TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="3263" />
<format octets="42310" target="ftp://ftp.isi.edu/in-notes/rfc3263.txt"
type="TXT" />
</reference>
<reference anchor="RFC4347">
<front>
<title>Datagram Transport Layer Security</title>
<author fullname="E. Rescorla" initials="E." surname="Rescorla">
<organization></organization>
</author>
<author fullname="N. Modadugu" initials="N." surname="Modadugu">
<organization></organization>
</author>
<date month="April" year="2006" />
<abstract>
<t>This document specifies Version 1.0 of the Datagram Transport
Layer Security (DTLS) protocol. The DTLS protocol provides
communications privacy for datagram protocols. The protocol allows
client/server applications to communicate in a way that is
designed to prevent eavesdropping, tampering, or message forgery.
The DTLS protocol is based on the Transport Layer Security (TLS)
protocol and provides equivalent security guarantees. Datagram
semantics of the underlying transport are preserved by the DTLS
protocol. [STANDARDS TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="4347" />
<format octets="56014" target="ftp://ftp.isi.edu/in-notes/rfc4347.txt"
type="TXT" />
</reference>
</references>
<references title="Informative References">
<reference anchor="I-D.ietf-p2psip-concepts">
<front>
<title>Concepts and Terminology for Peer to Peer SIP</title>
<author fullname="David Bryan" initials="D" surname="Bryan">
<organization></organization>
</author>
<date day="3" month="July" year="2007" />
<abstract>
<t>This document defines concepts and terminology for use of the
Session Initiation Protocol in a peer-to-peer environment where
the traditional proxy-registrar and message routing functions are
replaced by a distributed mechanism that might be implemented
using a distributed hash table or other distributed data mechanism
with similar external properties. This document includes a
high-level view of the functional relationships between the
network elements defined herein, a conceptual model of operations,
and an outline of the related open problems being addressed by the
P2PSIP working group. As this document matures, it is expected to
define the general framework for P2PSIP.</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft"
value="draft-ietf-p2psip-concepts-00" />
<format target="http://www.ietf.org/internet-drafts/draft-ietf-p2psip-concepts-00.txt"
type="TXT" />
</reference>
<reference anchor="RFC4145">
<front>
<title>TCP-Based Media Transport in the Session Description Protocol
(SDP)</title>
<author fullname="D. Yon" initials="D." surname="Yon">
<organization></organization>
</author>
<author fullname="G. Camarillo" initials="G." surname="Camarillo">
<organization></organization>
</author>
<date month="September" year="2005" />
<abstract>
<t>This document describes how to express media transport over TCP
using the Session Description Protocol (SDP). It defines the SDP
'TCP' protocol identifier, the SDP 'setup' attribute, which
describes the connection setup procedure, and the SDP 'connection'
attribute, which handles connection reestablishment. [STANDARDS
TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="4145" />
<format octets="30225" target="ftp://ftp.isi.edu/in-notes/rfc4145.txt"
type="TXT" />
</reference>
<reference anchor="RFC4572">
<front>
<title>Connection-Oriented Media Transport over the Transport Layer
Security (TLS) Protocol in the Session Description Protocol
(SDP)</title>
<author fullname="J. Lennox" initials="J." surname="Lennox">
<organization></organization>
</author>
<date month="July" year="2006" />
<abstract>
<t>This document specifies how to establish secure
connection-oriented media transport sessions over the Transport
Layer Security (TLS) protocol using the Session Description
Protocol (SDP). It defines a new SDP protocol identifier,
'TCP/TLS'. It also defines the syntax and semantics for an SDP
'fingerprint' attribute that identifies the certificate that will
be presented for the TLS session. This mechanism allows media
transport over TLS connections to be established securely, so long
as the integrity of session descriptions is
assured.</t><t> This document extends and updates RFC
4145. [STANDARDS TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="4572" />
<format octets="38658" target="ftp://ftp.isi.edu/in-notes/rfc4572.txt"
type="TXT" />
</reference>
<reference anchor="RFC2617">
<front>
<title abbrev="HTTP Authentication">HTTP Authentication: Basic and
Digest Access Authentication</title>
<author fullname="John Franks" initials="J." surname="Franks">
<organization>Northwestern University, Department of
Mathematics</organization>
<address>
<postal>
<street>Northwestern University</street>
<city>Evanston</city>
<region>IL</region>
<code>60208-2730</code>
<country>USA</country>
</postal>
<email>john@math.nwu.edu</email>
</address>
</author>
<author fullname="Phillip M. Hallam-Baker" initials="P.M."
surname="Hallam-Baker">
<organization>Verisign Inc.</organization>
<address>
<postal>
<street>301 Edgewater Place</street>
<street>Suite 210</street>
<city>Wakefield</city>
<region>MA</region>
<code>01880</code>
<country>USA</country>
</postal>
<email>pbaker@verisign.com</email>
</address>
</author>
<author fullname="Jeffery L. Hostetler" initials="J.L."
surname="Hostetler">
<organization>AbiSource, Inc.</organization>
<address>
<postal>
<street>6 Dunlap Court</street>
<city>Savoy</city>
<region>IL</region>
<code>61874</code>
<country>USA</country>
</postal>
<email>jeff@AbiSource.com</email>
</address>
</author>
<author fullname="Scott D. Lawrence" initials="S.D."
surname="Lawrence">
<organization>Agranat Systems, Inc.</organization>
<address>
<postal>
<street>5 Clocktower Place</street>
<street>Suite 400</street>
<city>Maynard</city>
<region>MA</region>
<code>01754</code>
<country>USA</country>
</postal>
<email>lawrence@agranat.com</email>
</address>
</author>
<author fullname="Paul J. Leach" initials="P.J." surname="Leach">
<organization>Microsoft Corporation</organization>
<address>
<postal>
<street>1 Microsoft Way</street>
<city>Redmond</city>
<region>WA</region>
<code>98052</code>
<country>USA</country>
</postal>
<email>paulle@microsoft.com</email>
</address>
</author>
<author fullname="Ari Luotonen" initials="A." surname="Luotonen">
<organization>Netscape Communications Corporation</organization>
<address>
<postal>
<street>501 East Middlefield Road</street>
<city>Mountain View</city>
<region>CA</region>
<code>94043</code>
<country>USA</country>
</postal>
</address>
</author>
<author fullname="Lawrence C. Stewart" initials="L."
surname="Stewart">
<organization>Open Market, Inc.</organization>
<address>
<postal>
<street>215 First Street</street>
<city>Cambridge</city>
<region>MA</region>
<code>02142</code>
<country>USA</country>
</postal>
<email>stewart@OpenMarket.com</email>
</address>
</author>
<date month="June" year="1999" />
<abstract>
<t>"HTTP/1.0", includes the specification for a Basic Access
Authentication scheme. This scheme is not considered to be a
secure method of user authentication (unless used in conjunction
with some external secure system such as SSL ), as the user name
and password are passed over the network as cleartext.</t>
<t>This document also provides the specification for HTTP's
authentication framework, the original Basic authentication scheme
and a scheme based on cryptographic hashes, referred to as "Digest
Access Authentication". It is therefore also intended to serve as
a replacement for RFC 2069 . Some optional elements specified by
RFC 2069 have been removed from this specification due to problems
found since its publication; other new elements have been added
for compatibility, those new elements have been made optional, but
are strongly recommended.</t>
<t>Like Basic, Digest access authentication verifies that both
parties to a communication know a shared secret (a password);
unlike Basic, this verification can be done without sending the
password in the clear, which is Basic's biggest weakness. As with
most other authentication protocols, the greatest sources of risks
are usually found not in the core protocol itself but in policies
and procedures surrounding its use.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="2617" />
<format octets="77638" target="ftp://ftp.isi.edu/in-notes/rfc2617.txt"
type="TXT" />
<format octets="114842"
target="http://xml.resource.org/public/rfc/html/rfc2617.html"
type="HTML" />
<format octets="87592"
target="http://xml.resource.org/public/rfc/xml/rfc2617.xml"
type="XML" />
</reference>
<reference anchor="RFC2818">
<front>
<title>HTTP Over TLS</title>
<author fullname="E. Rescorla" initials="E." surname="Rescorla">
<organization></organization>
</author>
<date month="May" year="2000" />
<abstract>
<t>This memo describes how to use Transport Layer Security (TLS)
to secure Hypertext Transfer Protocol (HTTP) connections over the
Internet. This memo provides information for the Internet
community.</t>
</abstract>
</front>
<seriesInfo name="RFC" value="2818" />
<format octets="15170" target="ftp://ftp.isi.edu/in-notes/rfc2818.txt"
type="TXT" />
</reference>
<reference anchor="RFC4086">
<front>
<title>Randomness Requirements for Security</title>
<author fullname="D. Eastlake" initials="D." surname="Eastlake">
<organization></organization>
</author>
<author fullname="J. Schiller" initials="J." surname="Schiller">
<organization></organization>
</author>
<author fullname="S. Crocker" initials="S." surname="Crocker">
<organization></organization>
</author>
<date month="June" year="2005" />
<abstract>
<t>Security systems are built on strong cryptographic algorithms
that foil pattern analysis attempts. However, the security of
these systems is dependent on generating secret quantities for
passwords, cryptographic keys, and similar quantities. The use of
pseudo-random processes to generate secret quantities can result
in pseudo-security. A sophisticated attacker may find it easier to
reproduce the environment that produced the secret quantities and
to search the resulting small set of possibilities than to locate
the quantities in the whole of the potential number
space.</t><t> Choosing random quantities to foil a
resourceful and motivated adversary is surprisingly difficult.
This document points out many pitfalls in using poor entropy
sources or traditional pseudo-random number generation techniques
for generating such quantities. It recommends the use of truly
random hardware techniques and shows that the existing hardware on
many systems can be used for this purpose. It provides suggestions
to ameliorate the problem when a hardware solution is not
available, and it gives examples of how large such quantities need
to be for some applications. This document specifies an Internet
Best Current Practices for the Internet Community, and requests
discussion and suggestions for improvements.</t>
</abstract>
</front>
<seriesInfo name="BCP" value="106" />
<seriesInfo name="RFC" value="4086" />
<format octets="114321"
target="ftp://ftp.isi.edu/in-notes/rfc4086.txt" type="TXT" />
</reference>
<reference anchor="RFC3280">
<front>
<title>Internet X.509 Public Key Infrastructure Certificate and
Certificate Revocation List (CRL) Profile</title>
<author fullname="R. Housley" initials="R." surname="Housley">
<organization></organization>
</author>
<author fullname="W. Polk" initials="W." surname="Polk">
<organization></organization>
</author>
<author fullname="W. Ford" initials="W." surname="Ford">
<organization></organization>
</author>
<author fullname="D. Solo" initials="D." surname="Solo">
<organization></organization>
</author>
<date month="April" year="2002" />
<abstract>
<t>This memo profiles the X.509 v3 certificate and X.509 v2
Certificate Revocation List (CRL) for use in the Internet.
[STANDARDS TRACK]</t>
</abstract>
</front>
<seriesInfo name="RFC" value="3280" />
<format octets="295556"
target="ftp://ftp.isi.edu/in-notes/rfc3280.txt" type="TXT" />
</reference>
<!--
<reference anchor="sosimple">
<front>
<title>SOSIMPLE: A Serverless, Standards-based, P2P SIP
Communication System</title>
<author fullname="David A. Bryan" initials="D. A." surname="Bryan">
<organization>College of William and Mary</organization>
</author>
<author fullname="Cullen Jennings" initials="C." surname="Jennings">
<organization>Cisco Systems</organization>
</author>
<author fullname="Bruce B. Lowekamp" initials="B. B."
surname="Lowekamp">
<organization>College of William and Mary</organization>
</author>
<date month="June" year="2005" />
</front>
<seriesInfo name="Proceedings of the 2005 International Workshop on Advanced Architectures and Algorithms for Internet Delivery and Applications (AAA-IDEA)"
value="'05" />
<format target="http://www.cs.wm.edu/~bryan/pubs/bryan-AAA-IDEA2005.pdf"
type="PDF" />
</reference>
<reference anchor="I-D.bryan-p2psip-dsip">
<front>
<title>dSIP: A P2P Approach to SIP Registration and Resource
Location</title>
<author fullname="D. Bryan" initials="D." surname="Bryan">
<organization></organization>
</author>
<author fullname="B. Lowekamp" initials="B." surname="Lowekamp">
<organization></organization>
</author>
<author fullname="C. Jennings" initials="C." surname="Jennings">
<organization></organization>
</author>
<date month="February" year="2007" />
</front>
<seriesInfo name="Internet Draft" value="draft-bryan-p2psip-dsip-00" />
</reference>
-->
<reference anchor="Sybil">
<front>
<title>The Sybil Attack</title>
<author fullname="John R. Douceur" initials="J. R."
surname="Douceur">
<organization>Microsoft Research</organization>
</author>
<date month="March" year="2002" />
</front>
<seriesInfo name="IPTPS" value="'02" />
<format target="http://www.cs.rice.edu/Conferences/IPTPS02/101.pdf"
type="PDF" />
</reference>
<reference anchor="Eclipse">
<front>
<title>"Eclipse Attacks on Overlay Networks: Threats and
Defenses"</title>
<author fullname="Atul Singh" initials="A." surname="Singh" />
<author fullname="Tsuen-Wan Ngan" initials="T. W." surname="Ngan" />
<author fullname="Peter Druschel" initials="T." surname="Druschel" />
<author fullname="Dan S. Wallach" initials="D. S." surname="Wallach" />
<seriesInfo name="INFOCOM" value="2006" />
</front>
</reference>
<reference anchor="I-D.cheshire-dnsext-multicastdns">
<front>
<title>Multicast DNS</title>
<author fullname="Stuart Cheshire" initials="S" surname="Cheshire">
<organization></organization>
</author>
<author fullname="Marc Krochmal" initials="M" surname="Krochmal">
<organization></organization>
</author>
<date day="25" month="August" year="2006" />
<abstract>
<t>As networked devices become smaller, more portable, and more
ubiquitous, the ability to operate with less configured
infrastructure is increasingly important. In particular, the
ability to look up DNS resource record data types (including, but
not limited to, host names) in the absence of a conventional
managed DNS server, is becoming essential. Multicast DNS (mDNS)
provides the ability to do DNS-like operations on the local link
in the absence of any conventional unicast DNS server. In
addition, mDNS designates a portion of the DNS namespace to be
free for local use, without the need to pay any annual fee, and
without the need to set up delegations or otherwise configure a
conventional DNS server to answer for those names. The primary
benefits of mDNS names are that (i) they require little or no
administration or configuration to set them up, (ii) they work
when no infrastructure is present, and (iii) they work during
infrastructure failures.</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft"
value="draft-cheshire-dnsext-multicastdns-06" />
<format target="http://www.ietf.org/internet-drafts/draft-cheshire-dnsext-multicastdns-06.txt"
type="TXT" />
</reference>
<reference anchor="I-D.cheshire-dnsext-dns-sd">
<front>
<title>DNS-Based Service Discovery</title>
<author fullname="Marc Krochmal" initials="M" surname="Krochmal">
<organization></organization>
</author>
<author fullname="Stuart Cheshire" initials="S" surname="Cheshire">
<organization></organization>
</author>
<date day="28" month="August" year="2006" />
<abstract>
<t>This document describes a convention for naming and structuring
DNS resource records. Given a type of service that a client is
looking for, and a domain in which the client is looking for that
service, this convention allows clients to discover a list of
named instances of that desired service, using only standard DNS
queries. In short, this is referred to as DNS-based Service
Discovery, or DNS-SD.</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft"
value="draft-cheshire-dnsext-dns-sd-04" />
<format target="http://www.ietf.org/internet-drafts/draft-cheshire-dnsext-dns-sd-04.txt"
type="TXT" />
</reference>
<!--
<reference anchor='I-D.jennings-p2psip-security'>
<front>
<title>Security Mechanisms for Peer to Peer SIP</title>
<author initials='C' surname='Jennings' fullname='Cullen Jennings'>
<organization />
</author>
<date month='February' day='27' year='2007' />
<abstract><t>This document describes an overview of some security mechanisms for P2P SIP. Specifically it discusses mechanisms that can be used to secure the stored data and the routing in the distributed storage. This draft is an very early draft to outline the possible solution space and far more details would be needed. This work is being discussed on the p2psip@ietf.org mailing list.</t></abstract>
</front>
<seriesInfo name='Internet-Draft' value='draft-jennings-p2psip-security-00' />
<format type='TXT'
target='http://www.ietf.org/internet-drafts/draft-jennings-p2psip-security-00.txt' />
</reference>
-->
<reference anchor="I-D.matthews-p2psip-bootstrap-mechanisms">
<front>
<title>Bootstrap Mechanisms for P2PSIP</title>
<author fullname="Eric Cooper" initials="E" surname="Cooper">
<organization></organization>
</author>
<date day="26" month="February" year="2007" />
<abstract>
<t>This document describes mechanisms that a peer can use to
locate and establish a Peer Protocol connection to an admitting
peer in order to join an overlay network. In the first mechanism,
the joining peer uses multicast to locate a bootstrap peer; in the
second, the node uses one or more bootstrap servers to locate a
bootstrap peer; in both cases, the bootstrap peer then proxies the
request by the joining peer on to the admitting peer. Each
mechanism has its advantages and disadvantages, and a node can
utilize both.</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft"
value="draft-matthews-p2psip-bootstrap-mechanisms-00" />
<format target="http://www.ietf.org/internet-drafts/draft-matthews-p2psip-bootstrap-mechanisms-00.txt"
type="TXT" />
</reference>
<reference anchor="I-D.garcia-p2psip-dns-sd-bootstrapping">
<front>
<title>P2PSIP bootstrapping using DNS-SD</title>
<author fullname="Gustavo Garcia" initials="G" surname="Garcia">
<organization></organization>
</author>
<date day="25" month="October" year="2007" />
<abstract>
<t>This document describes a DNS-based bootstrap mechanism to
discover the initial peer or peers needed to join a P2PSIP
Overlay. The document specifies the use of DNS Service Discovery
(DNS-SD) and the format of the required resource records to
support the discovery of P2PSIP peers. This mechanism can be
applied in scenarios with DNS servers or combined with multicast
DNS to fulfill different proposed P2PSIP use cases.</t>
</abstract>
</front>
<seriesInfo name="Internet-Draft"
value="draft-garcia-p2psip-dns-sd-bootstrapping-00" />
<format target="http://www.ietf.org/internet-drafts/draft-garcia-p2psip-dns-sd-bootstrapping-00.txt"
type="TXT" />
</reference>
</references>
</back>
</rfc>
| PAFTECH AB 2003-2026 | 2026-04-24 01:18:57 |