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Secure Inter-Domain Routing M. Lepinski
Working Group S. Kent
Internet Draft BBN Technologies
Intended status: Informational July 13, 2009
Expires: January 13, 2010
An Infrastructure to Support Secure Internet Routing
draft-ietf-sidr-arch-07.txt
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Abstract
This document describes an architecture for an infrastructure to
support improved security of Internet routing. The foundation of this
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architecture is a public key infrastructure (PKI) that represents the
allocation hierarchy of IP address space and Autonomous System
Numbers; and a distributed repository system for storing and
disseminating the data objects that comprise the PKI, as well as
other signed objects necessary for improved routing security. As an
initial application of this architecture, the document describes how
a legitimate holder of IP address space can explicitly and verifiably
authorize one or more ASes to originate routes to that address space.
Such verifiable authorizations could be used, for example, to more
securely construct BGP route filters.
Table of Contents
1. Introduction...................................................3
1.1. Terminology...............................................4
2. PKI for Internet Number Resources..............................5
2.1. Role in the overall architecture..........................5
2.2. CA Certificates...........................................6
2.3. End-Entity (EE) Certificates..............................7
2.4. Trust Anchors.............................................8
3. Route Origination Authorizations...............................9
3.1. Role in the overall architecture..........................9
3.2. Syntax and semantics......................................9
4. Repositories..................................................11
4.1. Role in the overall architecture.........................12
4.2. Contents and structure...................................12
4.3. Access protocols.........................................14
4.4. Access control...........................................14
5. Manifests.....................................................15
5.1. Syntax and semantics.....................................15
6. Local Cache Maintenance.......................................16
7. Common Operations.............................................17
7.1. Certificate issuance.....................................17
7.2. ROA management...........................................18
7.2.1. Single-homed subscribers (without provider independent
addresses).................................................19
7.2.2. Multi-homed subscribers (without provider independent
addresses).................................................19
7.2.3. Provider-Independent Address Space..................20
8. Security Considerations.......................................20
9. IANA Considerations...........................................20
10. Acknowledgments..............................................20
11. References...................................................22
11.1. Normative References....................................22
11.2. Informative References..................................22
Authors' Addresses...............................................23
Pre-5378 Material Disclaimer.....................................23
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1. Introduction
This document describes an architecture for an infrastructure to
support improved security for BGP routing [2] for the Internet. The
architecture encompasses three principle elements:
. a public key infrastructure (PKI)
. digitally-signed routing objects to support routing security
. a distributed repository system to hold the PKI objects and the
signed routing objects
The architecture described by this document enables an entity to
verifiably assert that it is the legitimate holder of a set of IP
addresses or a set of Autonomous System (AS) numbers. As an initial
application of this architecture, the document describes how a
legitimate holder of IP address space can explicitly and verifiably
authorize one or more ASes to originate routes to that address space.
Such verifiable authorizations could be used, for example, to more
securely construct BGP route filters. In addition to this initial
application, the infrastructure defined by this architecture also is
intended to provide future support for security protocols such as S-
BGP [11] or soBGP [12]. This architecture is applicable to the
routing of both IPv4 and IPv6 datagrams. IPv4 and IPv6 are currently
the only address families supported by this architecture. Thus, for
example, use of this architecture with MPLS labels is beyond the
scope of this document.
In order to facilitate deployment, the architecture takes advantage
of existing technologies and practices. The structure of the PKI
element of the architecture corresponds to the existing resource
allocation structure. Thus management of this PKI is a natural
extension of the resource-management functions of the organizations
that are already responsible for IP address and AS number resource
allocation. Likewise, existing resource allocation and revocation
practices have well-defined correspondents in this architecture. Note
that while the initial focus of this architecture is routing security
applications, the PKI described in this document could be used to
support other applications that make use of attestations of IP
address or AS number resource holdings.
To ease implementation, existing IETF standards are used wherever
possible; for example, extensive use is made of the X.509 certificate
profile defined by PKIX [3] and the extensions for IP Addresses and
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AS numbers representation defined in RFC 3779 [5]. Also CMS [4] is
used as the syntax for the newly-defined signed objects required by
this infrastructure.
As noted above, the architecture is comprised of three main
components: an X.509 PKI in which certificates attest to holdings of
IP address space and AS numbers; non-certificate/CRL signed objects
(including route origination authorizations and manifests) used by
the infrastructure; and a distributed repository system that makes
all of these signed objects available for use by ISPs in making
routing decisions. These three basic components enable several
security functions; this document describes how they can be used to
improve route filter generation, and to perform several other common
operations in such a way as to make them cryptographically
verifiable.
1.1. Terminology
It is assumed that the reader is familiar with the terms and concepts
described in "Internet X.509 Public Key Infrastructure Certificate
and Certificate Revocation List (CRL) Profile" [3], and "X.509
Extensions for IP Addresses and AS Identifiers" [5].
Throughout this document we use the terms "address space holder" or
"holder of IP address space" interchangeably to refer to a legitimate
holder of IP address space who has received this address space
through the standard IP address allocation hierarchy. That is, the
address space holder has either directly received the address space
as an allocation from a Regional Internet Registry (RIR) or IANA; or
else the address space holder has received the address space as a
sub-allocation from a National Internet Registry (NIR) or Local
Internet Registry (LIR). We use the term "resource holder" to refer
to a legitimate holder of either IP address or AS number resources.
Throughout this document we use the terms "registry" and ISP to refer
to an entity that has an IP address space and/or AS number allocation
that it is permitted to sub-allocate. We use the term "subscriber" to
refer to an entity (e.g., an enterprise) that receives an IP address
space and/or AS number allocation, but does not sub-allocate its
resources.
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 RFC-2119 [1].
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2. PKI for Internet Number Resources
Because the holder of a block IP address space is entitled to define
the topological destination of IP datagrams whose destinations fall
within that block, decisions about inter-domain routing are
inherently based on knowledge of the allocation of the IP address
space. Thus, a basic function of this architecture is to provide
cryptographically verifiable attestations as to these allocations. In
current practice, the allocation of IP addresses is hierarchic. The
root of the hierarchy is IANA. Below IANA are five Regional Internet
Registries (RIRs), each of which manages address and AS number
allocation within a defined geopolitical region. In some regions the
third tier of the hierarchy includes National Internet Registries
(NIRs) as well as Local Internet Registries (LIRs) and subscribers
with so-called provider-independent ("portable") allocations. (The
term LIR is used in some regions to refer to what other regions
define as an ISP. Throughout the rest of this document we will use
the term LIR/ISP to simplify references to these entities.) In other
regions the third tier consists only of LIRs/ISPs and subscribers
with provider-independent allocations.
In general, the holder of a block of IP address space may sub-
allocate portions of that block, either to itself (e.g., to a
particular unit of the same organization), or to another
organization, subject to contractual constraints established by the
registries. Because of this structure, IP address allocations can be
described naturally by a hierarchic public-key infrastructure, in
which each certificate attests to an allocation of IP addresses, and
issuance of subordinate certificates corresponds to sub-allocation of
IP addresses. The above reasoning holds true for AS number resources
as well, with the difference that, by convention, AS numbers may not
be sub-allocated except by RIRs or NIRs. Thus allocations of both IP
addresses and AS numbers can be expressed by the same PKI. Such a
PKI is a central component of this architecture.
2.1. Role in the overall architecture
Certificates in this PKI are called Resource Certificates, and
conform to the certificate profile for such certificates [6].
Resource certificates attest to the allocation by the (certificate)
issuer of IP addresses or AS numbers to the subject. They do this by
binding the public key contained in the Resource Certificate to the
IP addresses or AS numbers included in the certificate's IP Address
Delegation or AS Identifier Delegation Extensions, respectively, as
defined in RFC 3779 [5].
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An important property of this PKI is that certificates do not attest
to the identity of the subject. Therefore, the subject names used in
certificates are not intended to be "descriptive." That is, this PKI
is intended to provide authorization, but not authentication. This is
in contrast to most PKIs where the issuer ensures that the
descriptive subject name in a certificate is properly associated with
the entity that holds the private key corresponding to the public key
in the certificate. Because issuers need not verify the right of an
entity to use a subject name in a certificate, they avoid the costs
and liabilities of such verification. This makes it easier for these
entities to take on the additional role of Certificate Authority
(CA).
Most of the certificates in the PKI assert the basic facts on which
the rest of the infrastructure operates. CA certificates within the
PKI attest to IP address space and AS number holdings. End-entity
(EE) certificates are issued by resource holder CAs to delegate the
authority attested by their allocation certificates. The primary use
for EE certificates is the validation of Route Origination
Authorizations (ROAs). Additionally, signed objects called manifests
will be used to help ensure the integrity of the repository system,
and the signature on each manifest will be verified via an EE
certificate.
2.2. CA Certificates
Any resource holder who is authorized to sub-allocate these resources
must be able to issue Resource Certificates to correspond to these
sub-allocations. Thus, for example, CA certificates will be
associated with IANA and each of the RIRs, NIRs, and LIRs/ISPs. A CA
certificate also is required to enable a resource holder to issue
ROAs, because it must issue the corresponding end-entity certificate
used to validate each ROA. Thus some entities that do not sub-
allocate their resources also will need to have CA certificates for
their allocations, e.g., a multi-homed subscriber with a provider-
independent allocation, to enable them to issue ROAs. (A subscriber
who is not multi-homed, whose allocation comes from an LIR/ISP, and
who has not moved to a different LIR/ISP, need not be represented in
the PKI. Moreover, a multi-homed subscriber with an allocation from
an LIR/ISP may or may not need to be explicitly represented, as
discussed in Section 7.2.2)
Unlike in most PKIs, the distinguished name of the subject in a CA
certificate is chosen by the certificate issuer. The subject's
distinguished name must not attempt to convey the identity of the
subject in a descriptive fashion, and must be unique among all
certificates issued by a given authority. The subject's distinguished
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name must include the common name attribute and may additionally
include the serial attribute.
In this PKI, the certificate issuer, being an RIR, NIR, or LIR/ISP,
is not in the business of verifying the legal right of the subject to
assert a particular identity. Therefore, selecting a distinguished
name that does not convey the identity of the subject in a
descriptive fashion minimizes the opportunity for the subject to
misuse the certificate to assert an identity, and thus minimizes the
legal liability of the issuer. Since all CA certificates are issued
to subjects with whom the issuer has an existing relationship, it is
recommended that the issuer select a subject name that enables the
issuer to easily link the certificate to existing database records
associated with the subject. For example, an authority may use
internal database keys or subscriber IDs as the subject common name
in issued certificates.
Each Resource Certificate attests to an allocation of resources to a
resource holder, so entities that have allocations from multiple
sources will have multiple CA certificates. A CA also may issue
distinct certificates for each distinct allocation to the same
entity, if the CA and the resource holder agree that such an
arrangement will facilitate management and use of the certificates.
For example, an LIR/ISP may have several certificates issued to it by
one registry, each describing a distinct set of address blocks,
because the LIR/ISP desires to treat the allocations as separate.
2.3. End-Entity (EE) Certificates
The private key corresponding to public key contained in an EE
certificate is not used to sign other certificates in a PKI. The
primary function of end-entity certificates in this PKI is the
verification of signed objects that relate to the usage of the
resources described in the certificate, e.g., ROAs and manifests.
For ROAs and manifests there will be a one-to-one correspondence
between end-entity certificates and signed objects, i.e., the private
key corresponding to each end-entity certificate is used to sign
exactly one object, and each object is signed with only one key.
This property allows the PKI to be used to revoke these signed
objects, rather than creating a new revocation mechanism. When the
end-entity certificate used to sign an object has been revoked, the
signature on that object (and any corresponding assertions) will be
considered invalid, so a signed object can be effectively revoked by
revoking the end-entity certificate used to sign it.
A secondary advantage to this one-to-one correspondence is that the
private key corresponding to the public key in a certificate is used
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exactly once in its lifetime, and thus can be destroyed after it has
been used to sign its one object. This fact should simplify key
management, since there is no requirement to protect these private
keys for an extended period of time.
Although this document describes only two uses for end-entity
certificates, additional uses will likely be defined in the future.
For example, end-entity certificates could be used as a more general
authorization for their subjects to act on behalf of the specified
resource holder. This could facilitate authentication of inter-ISP
interactions, or authentication of interactions with the repository
system. These additional uses for end-entity certificates may
require retention of the corresponding private keys, even though this
is not required for the private keys associated with end-entity
certificates keys used for verification of ROAs and manifests, as
described above.
2.4. Trust Anchors
In any PKI, each relying party (RP) chooses its own set of trust
anchors. This general property of PKIs applies here as well. There is
an extant IP address space and AS number allocation hierarchy, and
thus IANA and/or the five RIRs are obvious candidates to be default
TAs here. Nonetheless, each RP ultimately chooses the set of trust
anchors it will use for certificate validation.
For example, a RP (e.g., an LIR/ISP) could create a trust anchor to
which all address space and/or all AS numbers are assigned, and for
which the RP knows the corresponding private key. The RP could then
issue certificates under this trust anchor to whatever entities in
the PKI it wishes, with the result that the certification paths
terminating at this locally-installed trust anchor will satisfy the
RFC 3779 validation requirements. A large ISP that uses private
(i.e., RFC 1918) IP address space and runs BGP internally will need
to create this sort of trust anchor to accommodate a CA to which all
private (RFC 1918) address space is assigned. The RP could then issue
certificates under this CA that correspond to the RP's internal use
of private address space.
Note that a RP who elects to create and manage its own set of trust
anchors may fail to detect allocation errors that arise under such
circumstances, but the resulting vulnerability is local to the RP.
It is expected that some parties within the extant IP address space
and AS number allocation hierarchy may wish to publish trust anchor
material for possible use by relying parties. A standard profile for
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the publication of trust anchor material for this public key
infrastructure can be found in [9].
3. Route Origination Authorizations
The information on IP address allocation provided by the PKI is not,
in itself, sufficient to guide routing decisions. In particular, BGP
is based on the assumption that the AS that originates routes for a
particular prefix is authorized to do so by the holder of that prefix
(or an address block encompassing the prefix); the PKI contains no
information about these authorizations. A Route Origination
Authorization (ROA) makes such authorization explicit, allowing a
holder of IP address space to create an object that explicitly and
verifiably asserts that an AS is authorized originate routes to a
given set of prefixes.
3.1. Role in the overall architecture
A ROA is an attestation that the holder of a set of prefixes has
authorized an autonomous system to originate routes for those
prefixes. A ROA is structured according to the format described in
[7]. The validity of this authorization depends on the signer of the
ROA being the holder of the prefix(es) in the ROA; this fact is
asserted by an end-entity certificate from the PKI, whose
corresponding private key is used to sign the ROA.
ROAs may be used by relying parties to verify that the AS that
originates a route for a given IP address prefix is authorized by the
holder of that prefix to originate such a route. For example, an ISP
might use validated ROAs as inputs to route filter construction for
use by its BGP routers. (See [14] for information on the use of ROAs
to validate the origination of BGP routes.)
Initially, the repository system will be the primary mechanism for
disseminating ROAs, since these repositories will hold the
certificates and CRLs needed to verify ROAs. In addition, ROAs also
could be distributed in BGP UPDATE messages or via other
communication paths, if needed to meet timeliness requirements.
3.2. Syntax and semantics
A ROA constitutes an explicit authorization for a single AS to
originate routes to one or more prefixes, and is signed by the holder
of those prefixes. A detailed specification of the ROA syntax can be
found in [7] but, at a high level, a ROA consists of (1) an AS
number; (2) a list of IP address prefixes; and, optionally, (3) for
each prefix, the maximum length of more specific (longer) prefixes
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that the AS is also authorized to advertise. (This last element
facilitates a compact authorization to advertise, for example, any
prefixes of length 20 to 24 contained within a given length 20
prefix.)
Note that a ROA contains only a single AS number. Thus, if an ISP has
multiple AS numbers that will be authorized to originate routes to
the prefix(es) in the ROA, an address space holder will need to issue
multiple ROAs to authorize the ISP to originate routes from any of
these ASes.
A ROA is signed using the private key corresponding to the public key
in an end-entity certificate in the PKI. In order for a ROA to be
valid, its corresponding end-entity (EE) certificate must be valid
and the IP address prefixes of the ROA must exactly match the IP
address prefix(es) specified in the EE certificate's RFC 3779
extension. Therefore, the validity interval of the ROA is implicitly
the validity interval of its corresponding certificate. A ROA is
revoked by revoking the corresponding EE certificate. There is no
independent method of invoking a ROA. One might worry that this
revocation model could lead to long CRLs for the CA certification
that is signing the EE certificates. However, routing announcements
on the public internet are generally quite long lived. Therefore, as
long as the EE certificates used to verify a ROA are given a validity
interval of several months, the likelihood that many ROAs would need
to revoked within that time is quite low.
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--------- ---------
| RIR | | NIR |
| CA | | CA |
--------- ---------
| |
| |
| |
--------- ---------
| ISP | | ISP |
| CA 1 | | CA 2 |
--------- ---------
| \ |
| ----- |
| \ |
---------- ---------- ----------
| ISP | | ISP | | ISP |
| EE 1a | | EE 1b | | EE 2 |
---------- ---------- ----------
| | |
| | |
| | |
---------- ---------- ----------
| ROA 1a | | ROA 1b | | ROA 2 |
---------- ---------- ----------
FIGURE 2: This figure illustrates an ISP with allocations from two
sources (and RIR and an NIR). It needs two CA certificates due to RFC
3779 rules.
Because each ROA is associated with a single end-entity certificate,
the set of IP prefixes contained in a ROA must be drawn from an
allocation by a single source, i.e., a ROA cannot combine allocations
from multiple sources. Address space holders who have allocations
from multiple sources, and who wish to authorize an AS to originate
routes for these allocations, must issue multiple ROAs to the AS.
4. Repositories
Initially, an LIR/ISP will make use of the resource PKI by acquiring
and validating every ROA, to create a table of the prefixes for which
each AS is authorized to originate routes. To validate all ROAs, an
LIR/ISP needs to acquire all the certificates and CRLs. The primary
function of the distributed repository system described here is to
store these signed objects and to make them available for download by
LIRs/ISPs. Note that this repository system provides a mechanism by
which relying parties can pull fresh data at whatever frequency they
deem appropriate. However, it does not provide a mechanism for
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pushing fresh data to relying parties (e.g. by including resource PKI
objects in BGP or other protocol messages) and such a mechanism is
beyond the scope of the current document.
The digital signatures on all objects in the repository ensure that
unauthorized modification of valid objects is detectable by relying
parties. Additionally, the repository system uses manifests (see
Section 5) to ensure that relying parties can detect the deletion of
valid objects and the insertion of out of date, valid signed objects.
The repository system is also a point of enforcement for access
controls for the signed objects stored in it, e.g., ensuring that
records related to an allocation of resources can be manipulated only
by authorized parties. The use of access controls prevents denial of
service attacks based on deletion of or tampering to repository
objects. Indeed, although relying parties can detect tampering with
objects in the repository, it is preferable that the repository
system prevent such unauthorized modifications to the greatest extent
possible.
4.1. Role in the overall architecture
The repository system is the central clearing-house for all signed
objects that must be globally accessible to relying parties. When
certificates and CRLs are created, they are uploaded to this
repository, and then downloaded for use by relying parties (primarily
LIRs/ISPs). ROAs and manifests are additional examples of such
objects, but other types of signed objects may be added to this
architecture in the future. This document briefly describes the way
signed objects (certificates, CRLs, ROAs and manifests) are managed
in the repository system. As other types of signed objects are added
to the repository system it will be necessary to modify the
description, but it is anticipated that most of the design principles
will still apply. The repository system is described in detail in
[10].
4.2. Contents and structure
Although there is a single repository system that is accessed by
relying parties, it is comprised of multiple databases. These
databases will be distributed among registries (RIRs, NIRs,
LIRs/ISPs). At a minimum, the database operated by each registry will
contain all CA and EE certificates, CRLs, and manifests signed by the
CA(s) associated with that registry. Repositories operated by
LIRs/ISPs also will contain ROAs. Registries are encouraged to
maintain copies of repository data from their customers, and their
customer's customers (etc.), to facilitate retrieval of the whole
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repository contents by relying parties. Ideally, each RIR will hold
PKI data from all entities within its geopolitical scope.
For every certificate in the PKI, there will be a corresponding file
system directory in the repository that is the authoritative
publication point for all objects (certificates, CRLs, ROAs and
manifests) verifiable via this certificate. A certificate's Subject
Information Authority (SIA) extension provides a URI that references
this directory. Additionally, a certificate's Authority Information
Authority (AIA) extension contains a URI that references the
authoritative location for the CA certificate under which the given
certificate was issued. That is, if certificate A is used to verify
certificate B, then the AIA extension of certificate B points to
certificate A, and the SIA extension of certificate A points to a
directory containing certificate B (see Figure 2).
+--------+
+--------->| Cert A |<----+
| | CRLDP | | +---------+
| | AIA | | +-->| A's CRL |<-+
| +--------- SIA | | | +---------+ |
| | +--------+ | | |
| | | | |
| | +---+----+ |
| | | | |
| | +---------------|---|-----------------+ |
| | | | | | |
| +->| +--------+ | | +--------+ | |
| | | Cert B | | | | Cert C | | |
| | | CRLDP ----+ | | CRLDP -+--------+
+----------- AIA | +----- AIA | |
| | SIA | | SIA | |
| +--------+ +--------+ |
| |
+-------------------------------------+
FIGURE 3: In this example, certificates B and C are issued under
certificate A. Therefore, the AIA extensions of certificates B and C
point to A, and the SIA extension of certificate A points to the
directory containing certificates B and C.
If a CA certificate is reissued with the same public key, it should
not be necessary to reissue (with an updated AIA URI) all
certificates signed by the certificate being reissued. Therefore, a
certification authority SHOULD use a persistent URI naming scheme for
issued certificates. That is, reissued certificates should use the
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same publication point as previously issued certificates having the
same subject and public key, and should overwrite such certificates.
4.3. Access protocols
Repository operators will choose one or more access protocols that
relying parties can use to access the repository system. These
protocols will be used by numerous participants in the infrastructure
(e.g., all registries, ISPs, and multi-homed subscribers) to maintain
their respective portions of it. In order to support these
activities, certain basic functionality is required of the suite of
access protocols, as described below. No single access protocol need
implement all of these functions (although this may be the case), but
each function must be implemented by at least one access protocol.
Download: Access protocols MUST support the bulk download of
repository contents and subsequent download of changes to the
downloaded contents, since this will be the most common way in which
relying parties interact with the repository system. Other types of
download interactions (e.g., download of a single object) MAY also be
supported.
Upload/change/delete: Access protocols MUST also support mechanisms
for the issuers of certificates, CRLs, and other signed objects to
add them to the repository, and to remove them. Mechanisms for
modifying objects in the repository MAY also be provided. All access
protocols that allow modification to the repository (through
addition, deletion, or modification of its contents) MUST support
verification of the authorization of the entity performing the
modification, so that appropriate access controls can be applied (see
Section 4.4).
Current efforts to implement a repository system use RSYNC [13] as
the single access protocol. RSYNC, as used in this implementation,
provides all of the above functionality. A document specifying the
conventions for use of RSYNC in the PKI will be prepared.
4.4. Access control
In order to maintain the integrity of information in the repository,
controls must be put in place to prevent addition, deletion, or
modification of objects in the repository by unauthorized parties.
The identities of parties attempting to make such changes can be
authenticated through the relevant access protocols. Although
specific access control policies are subject to the local control of
repository operators, it is recommended that repositories allow only
the issuers of signed objects to add, delete, or modify them.
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Alternatively, it may be advantageous in the future to define a
formal delegation mechanism to allow resource holders to authorize
other parties to act on their behalf, as suggested in Section 2.3
above.
5. Manifests
A manifest is a signed object listing of all of the signed objects
issued by an authority responsible for a publication in the
repository system. For each certificate, CRL, or ROA issued by the
authority, the manifest contains both the name of the file containing
the object, and a hash of the file content.
As with ROAs, a manifest is signed by a private key, for which the
corresponding public key appears in an end-entity certificate. This
EE certificate, in turn, is signed by the CA in question. The EE
certificate private key may be used to issue one for more manifests.
If the private key is used to sign only a single manifest, then the
manifest can be revoked by revoking the EE certificate. In such a
case, to avoid needless CRL growth, the EE certificate used to
validate a manifest SHOULD expire at the same time that the manifest
expires. If an EE certificate is used to issue multiple (sequential)
manifests for the CA in question, then there is no revocation
mechanism for these individual manifests.
Manifests may be used by relying parties when constructing a local
cache (see Section 6) to mitigate the risk of an attacker who deletes
files from a repository or replaces current signed objects with stale
versions of the same object. Such protection is needed because
although all objects in the repository system are signed, the
repository system itself is untrusted.
5.1. Syntax and semantics
A manifest constitutes a list of (the hashes of) all the files in a
repository point at a particular point in time. A detailed
specification of manifest syntax is provided in [8] but, at a high
level, a manifest consists of (1) a manifest number; (2) the time the
manifest was issued; (3) the time of the next planned update; and (4)
a list of filename and hash value pairs.
The manifest number is a sequence number that is incremented each
time a manifest is issued by the authority. An authority is required
to issue a new manifest any time it alters any of its items in the
repository, or when the specified time of the next update is reached.
A manifest is thus valid until the specified time of the next update
or until a manifest is issued with a greater manifest number,
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whichever comes first. (Note that when an EE certificate is used to
sign only a single manifest, whenever the authority issues the new
manifest, the CA MUST also issue a new CRL which includes the EE
certificate corresponding to the old manifest. The revoked EE
certificate for the old manifest will be removed from the CRL when it
expires, thus this procedure ought not to result in significant CRLs
growth.)
6. Local Cache Maintenance
In order to utilize signed objects issued under this PKI, a relying
party must first obtain a local copy of the valid EE certificates for
the PKI. To do so, the relying party performs the following steps:
1. Query the registry system to obtain a copy of all certificates,
manifests and CRLs issued under the PKI.
2. For each CA certificate in the PKI, verify the signature on the
corresponding manifest. Additionally, verify that the current
time is earlier than the time indicated in the nextUpdate field
of the manifest.
3. For each manifest, verify that certificates and CRLs issued
under the corresponding CA certificate match the hash values
contained in the manifest. Additionally, verify that no
certificate or manifest listed on the manifest is missing from
the repository. If the hash values do not match, or if any
certificate or CRL is missing, notify the appropriate repository
administrator that the repository data has been corrupted.
4. Validate each EE certificate by constructing and verifying a
certification path for the certificate (including checking
relevant CRLs) to the locally configured set of TAs. (See [6]
for more details.)
Note that when a relying party performs these operations regularly,
it is more efficient for the relying party to request from the
repository system only those objects that have changed since the
relying party last updated its local cache. A relying party may
choose any frequency it desires for downloading and validating
updates from the repository. However, a typical ISP might reasonably
choose to perform these operations on a daily schedule. Note also
that by checking all issued objects against the appropriate manifest,
the relying party can be certain that it is not missing an updated
version of any object.
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7. Common Operations
Creating and maintaining the infrastructure described above will
entail additional operations as "side effects" of normal resource
allocation and routing authorization procedures. For example, a
subscriber with provider-independent ("portable") address space who
enters a relationship with an ISP will need to issue one or more ROAs
identifying that ISP, in addition to conducting any other necessary
technical or business procedures. The current primary use of this
infrastructure is for route filter construction; using ROAs, route
filters can be constructed in an automated fashion with high
assurance that the holder of the advertised prefix has authorized the
origin AS to originate an advertised route.
7.1. Certificate issuance
There are several operational scenarios that require certificates to
be issued. Any allocation that may be sub-allocated requires a CA
certificate, e.g., so that certificates can be issued as necessary
for the sub-allocations. Holders of provider-independent IP address
space allocations also must have certificates, so that a ROA can be
issued to each ISP that is authorized to originate a route to the
allocation (since the allocation does not come from any ISP).
Additionally, multi-homed subscribers may require certificates for
their allocations if they intend to issue the ROAs for their
allocations (see Section 7.2.2). Other resource holders need not be
issued CA certificates within the PKI.
In the long run, a resource holder will not request resource
certificates, but rather receive a certificate as a side effect of
the allocation process for the resource. However, initial deployment
of the RPKI will entail issuance of certificates to existing resource
holders as an explicit event. Note that in all cases, the authority
issuing a CA certificate will be the entity who allocates resources
to the subject. This differs from most PKIs in which a subject can
request a certificate from any certification authority.
If a resource holder receives multiple allocations over time, it may
accrue a collection of resource certificates to attest to them. If a
resource holder receives multiple allocations from the same source,
the set of resource certificates may be combined into a single
resource certificate, if both the issuer and the resource holder
agree. This is accomplished by consolidating the IP Address
Delegation and AS Identifier Delegation Extensions into a single
extension (of each type) in a new certificate. However, if the
certificates for these allocations contain different validity
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intervals, creating a certificate that combines them might create
problems, and thus is NOT RECOMMENDED.
If a resource holder's allocations come from different sources, they
will be signed by different CAs, and cannot be combined. When a set
of resources is no longer allocated to a resource holder, any
certificates attesting to such an allocation MUST be revoked. A
resource holder SHOULD NOT use the same public key in multiple CA
certificates that are issued by the same or differing authorities, as
reuse of a key pair complicates path construction. Note that since
the subject's distinguished name is chosen by the issuer, a subject
who receives allocations from two sources generally will receive
certificates with different subject names.
7.2. ROA management
Whenever a holder of IP address space wants to authorize an AS to
originate routes for a prefix within his holdings, he MUST issue an
end-entity certificate containing that prefix in an IP Address
Delegation extension. He then uses the corresponding private key to
sign a ROA containing the designated prefix and the AS number for the
AS. The resource holder MAY include more than one prefix in the EE
certificate and corresponding ROA if desired. As a prerequisite,
then, any address space holder that issues ROAs for a prefix must
have a resource certificate for an allocation containing that prefix.
The standard procedure for issuing a ROA is as follows:
1. Create an end-entity certificate containing the prefix(es) to be
authorized in the ROA.
2. Construct the payload of the ROA, including the prefixes in the
end-entity certificate and the AS number to be authorized.
3. Sign the ROA using the private key corresponding to the end-
entity certificate (the ROA is comprised of the payload
encapsulated in a CMS signed message [7]).
4. Upload the end-entity certificate and the ROA to the repository
system.
The standard procedure for revoking a ROA is to revoke the
corresponding end-entity certificate by creating an appropriate CRL
and uploading it to the repository system. The revoked ROA and end-
entity certificate SHOULD BE removed from the repository system.
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7.2.1. Single-homed subscribers (without provider independent addresses)
In BGP, a single-homed subscriber with provider allocated (non-
portable) address space does not need to explicitly authorize routes
to be originated for the prefix(es) it is using, since its ISP will
already advertise a more general prefix and route traffic for the
subscriber's prefix as an internal function. Since no routes are
originated specifically for prefixes held by these subscribers, no
ROAs need to be issued under their allocations; rather, the
subscriber's ISP will issue any necessary ROAs for its more general
prefixes under resource certificates from its own allocation. Thus, a
single-homed subscriber with an IP address allocation from his
service provider is not included in the RPKI, i.e., it does not
receive a CA certificate, nor issue EE certificates or ROAs.
7.2.2. Multi-homed subscribers (without provider independent addresses)
Here we consider a subscriber who receives IP address space from a
primary ISP (i.e., the IP addresses used by the subscriber are a
subset of ISP A's IP address space allocation) and receives redundant
upstream connectivity from the primary ISP, as well as one or more
secondary ISPs. The preferred option for such a multi-homed
subscribers is for the subscriber to obtain an AS number (from an RIR
or NIR) and run BGP with each of its upstream providers. In such a
case, there are two ways for ROA management to be handled. The first
is that the primary ISP issues a CA certificate to the subscriber,
and the subscriber issues a ROA to containing the subscriber's AS
number and the subscriber's IP address prefixes. The second
possibility is that the primary ISP does not issue a ROA to the
subscriber, and instead issues a ROA on the subscriber's behalf that
contains the subscriber's AS number and the subscriber's IP address
prefixes.
If the subscriber is unable or unwilling to obtain an AS number and
run BGP, the other option is that the multi-homed subscriber can
request that the primary ISP create a ROA for each secondary ISP that
authorizes the secondary ISP to originate routes to the subscriber's
prefixes. The primary ISP will also create a ROA containing its own
AS number and the subscriber's prefixes, as it is likely in such a
case that the primary ISP wishes to advertise precisely the
subscriber's prefixes and not an encompassing aggregate. Note that
this approach results in inconsistent origin AS numbers for the
subscribers prefixes which are considered undesirable on the public
Internet; thus this approach is NOT RECOMMENDED.
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7.2.3. Provider-Independent Address Space
A resource holder is said to have provider-independent (portable)
address space if the resource holder received its allocation directly
from a RIR or NIR. Because the prefixes represented in such
allocations are not taken from an allocation held by an ISP, there is
no ISP that holds and advertises a more general prefix. A holder of a
portable IP address space allocation MUST authorize one or more ASes
to originate routes to these prefixes. Thus the resource holder MUST
generate one or more EE certificates and associated ROAs to enable
the AS(es) to originate routes for the prefix(es) in question. This
ROA is required because none of the ISP's existing ROAs authorize it
to originate routes to the subscriber's provider-idependent
allocation.
8. Security Considerations
The focus of this document is security; hence security considerations
permeate this specification.
The security mechanisms provided by and enabled by this architecture
depend on the integrity and availability of the infrastructure it
describes. The integrity of objects within the infrastructure is
ensured by appropriate controls on the repository system, as
described in Section 4.4. Likewise, because the repository system is
structured as a distributed database, it should be inherently
resistant to denial of service attacks; nonetheless, appropriate
precautions should also be taken, both through replication and backup
of the constituent databases and through the physical security of
database servers.
9. IANA Considerations
This document requests that the IANA issue RPKI Certificates for the
resources for which it is authoritative, i.e., reserved IPv4
addresses, IPv6 ULAs, and address space not yet allocated by IANA to
the RIRs. IANA SHOULD make available trust anchor material in the
format defined in [10] in support of these functions.
10. Acknowledgments
The architecture described in this draft is derived from the
collective ideas and work of a large group of individuals. This work
would not have been possible without the intellectual contributions
of George Michaelson, Robert Loomans, Sanjaya and Geoff Huston of
APNIC, Robert Kisteleki and Henk Uijterwaal of the RIPE NCC, Tim
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Christensen and Cathy Murphy of ARIN, Rob Austein of ISC and Randy
Bush of IIJ.
Although we are indebted to everyone who has contributed to this
architecture, we would like to especially thank Rob Austein for the
concept of a manifest, Geoff Huston for the concept of managing
object validity through single-use EE certificate key pairs, and
Richard Barnes for help in preparing an early version of this
document.
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11. References
11.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] Rekhter, Y., Li, T., and S. Hares, "A Border Gateway Protocol 4
(BGP-4)", RFC 4271, January 2006
[3] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., Housley,
R., and W. Polk, "Internet X.509 Public Key Infrastructure
Certificate and Certificate Revocation List (CRL) Profile", RFC
5280, May 2008.
[4] Housley, R., "Cryptographic Message Syntax", RFC 3852, July
2004.
[5] Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
Addresses and AS Identifiers", RFC 3779, June 2004.
[6] Huston, G., Michaelson, G., and Loomans, R., "A Profile for
X.509 PKIX Resource Certificates", draft-ietf-sidr-res-certs-
16, February 2009.
[7] Lepinski, M., Kent, S., and Kong, D., "A Profile for Route
Origin Authorizations (ROA)", draft-ietf-sidr-roa-format-04,
November 2008.
[8] Austein, R., et al., "Manifests for the Resource Public Key
Infrastructure", draft-ietf-sidr-rpki-manifests-04, October
2008.
[9] Michaelson, G., Kent, S., and Huston, G., "A Profile for Trust
Anchor Material for the Resource Certificate PKI", draft-ietf-
sidr-ta-00, February 2009.
11.2. Informative References
[10] Huston, G., Michaelson, G., and Loomans, R., "A Profile for
Resource Certificate Repository Structure", draft-ietf-sidr-
repos-struct-01, October 2008.
[11] Kent, S., Lynn, C., and Seo, K., "Secure Border Gateway
Protocol (Secure-BGP)", IEEE Journal on Selected Areas in
Communications Vol. 18, No. 4, April 2000.
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[12] White, R., "soBGP", May 2005, <ftp://ftp-
eng.cisco.com/sobgp/index.html>
[13] Tridgell, A., "rsync", April 2006,
<http://samba.anu.edu.au/rsync/>
[14] Huston, G., Michaelson, G., "Validation of Route Origination in
BGP using the Resource Certificate PKI", draft-ietf-sidr-roa-
validation-01, October 2008.
Authors' Addresses
Matt Lepinski
BBN Technologies
10 Moulton St.
Cambridge, MA 02138
Email: mlepinski@bbn.com
Stephen Kent
BBN Technologies
10 Moulton St.
Cambridge, MA 02138
Email: kent@bbn.com
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Without obtaining an adequate license from the person(s) controlling
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outside the IETF Standards Process, and derivative works of it may
not be created outside the IETF Standards Process, except to format
it for publication as an RFC or to translate it into languages other
than English.
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