One document matched: draft-ietf-roll-security-threats-05.xml
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<rfc category="info" docName="draft-ietf-roll-security-threats-05"
ipr="trust200902">
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<!-- ***** FRONT MATTER ***** -->
<front>
<!-- The abbreviated title is used in the page header - it is only necessary if the full title is longer than 39 characters -->
<title abbrev="Security Threat Analysis for ROLL">A Security Threat
Analysis for Routing over Low-Power and Lossy Networks</title>
<!-- add 'role="editor"' below for the editors if appropriate -->
<!-- Another author who claims to be an editor -->
<author fullname="Tzeta Tsao" initials="T." surname="Tsao">
<organization>Cooper Power Systems</organization>
<address>
<postal>
<street>910 Clopper Rd. Suite 201S</street>
<!-- Reorder these if your country does things differently -->
<city>Gaithersburg</city>
<region>Maryland</region>
<code>20878</code>
<country>USA</country>
</postal>
<email>tzeta.tsao@cooperindustries.com</email>
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</address>
</author>
<author fullname="Roger K. Alexander" initials="R.K." surname="Alexander">
<organization>Cooper Power Systems</organization>
<address>
<postal>
<street>910 Clopper Rd. Suite 201S</street>
<!-- Reorder these if your country does things differently -->
<city>Gaithersburg</city>
<region>Maryland</region>
<code>20878</code>
<country>USA</country>
</postal>
<email>roger.alexander@cooperindustries.com</email>
<!-- uri and facsimile elements may also be added -->
</address>
</author>
<author fullname="Mischa Dohler" initials="M." surname="Dohler">
<organization>CTTC</organization>
<address>
<postal>
<street>Parc Mediterrani de la Tecnologia, Av. Canal Olimpic
S/N</street>
<!-- Reorder these if your country does things differently -->
<code>08860</code>
<city>Castelldefels</city>
<region>Barcelona</region>
<country>Spain</country>
</postal>
<email>mischa.dohler@cttc.es</email>
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</address>
</author>
<author fullname="Vanesa Daza" initials="V." surname="Daza">
<organization>Universitat Pompeu Fabra</organization>
<address>
<postal>
<street>P/ Circumval.lacio 8, Oficina 308</street>
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<code>08003</code>
<region>Barcelona</region>
<country>Spain</country>
</postal>
<email>vanesa.daza@upf.edu</email>
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</author>
<author fullname="Angel Lozano" initials="A." surname="Lozano">
<organization>Universitat Pompeu Fabra</organization>
<address>
<postal>
<street>P/ Circumval.lacio 8, Oficina 309</street>
<!-- Reorder these if your country does things differently -->
<code>08003</code>
<region>Barcelona</region>
<country>Spain</country>
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<email>angel.lozano@upf.edu</email>
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</address>
</author>
<author fullname="Michael Richardson (ed)" initials="M." surname="Richardson">
<organization>Sandelman Software Works</organization>
<address>
<postal>
<street>470 Dawson Avenue</street>
<city>Ottawa</city>
<region>ON</region>
<code>K1Z5V7</code>
<country>Canada</country>
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<email>mcr+ietf@sandelman.ca</email>
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</author>
<date year="2013"/>
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<!-- Meta-data Declarations -->
<area>Routing</area>
<workgroup>Routing Over Low-Power and Lossy Networks</workgroup>
<!-- WG name at the upperleft corner of the doc, IETF is fine for individual submissions. If this element is not present, the default is "Network Working Group", which is used by the RFC Editor as a nod to the history of the IETF. -->
<keyword>LLN, ROLL, security</keyword>
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<abstract>
<t>This document presents a security threat
analysis for routing over low-power and lossy networks (LLN). The
development builds upon previous work on routing security and adapts the
assessments to the issues and constraints specific to low-power and
lossy networks. A systematic approach is used in defining and evaluating
the security threats. Applicable countermeasures are application
specific and are addressed in relevant applicability statements. These
assessments provide the basis of the security recommendations for
incorporation into low-power, lossy network routing protocols.</t>
</abstract>
<note title="Requirements Language">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in <xref
target="RFC2119">RFC 2119</xref>.</t>
</note>
</front>
<middle>
<section anchor="intro" title="Introduction">
<t>In recent times, networked electronic devices have found an
increasing number of applications in various fields. Yet, for reasons
ranging from operational application to economics, these wired and
wireless devices are often supplied with minimum physical resources; the
constraints include those on computational resources (RAM, clock speed,
storage), communication resources (duty cycle, packet size, etc.), but
also form factors that may rule out user access interfaces (e.g., the
housing of a small stick-on switch), or simply safety considerations
(e.g., with gas meters). As a consequence, the resulting networks are
more prone to loss of traffic and other vulnerabilities. The
proliferation of these low-power and lossy networks (LLNs), however, are
drawing efforts to examine and address their potential networking
challenges. Securing the establishment and maintenance of network
connectivity among these deployed devices becomes one of these key
challenges.</t>
<t>This document presents a threat analysis for securing Routing Over
LLNs (ROLL) through an analysis that starts from the routing basics.
The process requires two steps.
First, the analysis will be used to identify pertinent security issues.
The second step is to identify necessary countermeasures to secure the
ROLL protocols. As there are multiple ways to solve the problem and
the specific tradeoffs are deployment specific, the specific
countermeasure to be used is detailed in applicatbility statements.</t>
<t>This document uses [IS07498-2] model, which includes Authentication,
Access Control, Data Confidentiality, Data Integrity, and
Non-Repudiation but to which Availability is added.</t>
<t>All of this document concerns itself with control plane traffic
only.</t>
</section>
<section title="Terminology">
<t>This document adopts the terminology defined in <xref
target="RFC6550"/>, in <xref target="RFC4949"/>, and in
<xref target="I-D.ietf-roll-terminology" />.
</t>
<t>The terms control plane and forwarding plane are used
consistently with section 1 of <xref target="RFC6192"/>.
</t>
</section>
<section anchor="cons-on-roll-sec" title="Considerations on ROLL Security">
<t>Routing security, in essence, ensures that the routing protocol
operates correctly. It entails implementing measures to ensure
controlled state changes on devices and network elements, both based on
external inputs (received via communications) or internal inputs
(physical security of device itself and parameters maintained by the
device, including, e.g., clock). State changes would thereby involve not
only authorization of injector's actions, authentication of injectors,
and potentially confidentiality of routing
data, but also proper order of state changes through timeliness, since
seriously delayed state changes, such as commands or updates of routing
tables, may negatively impact system operation. A security assesment can
therefore begin with a focus on the assets <xref target="RFC4949" />
that may be the target of the state
changes and the access points in terms of interfaces and protocol
exchanges through which such changes may occur. In the case of routing
security the focus is directed towards the elements associated with the
establishment and maintenance of network connectivity.</t>
<t>This section sets the stage for the development of the analysis by
applying the systematic approach proposed in <xref
target="Myagmar2005"/> to the routing security, while also drawing
references from other reviews and assessments found in the literature,
particularly, <xref target="RFC4593"/> and <xref target="Karlof2003"/>.
The subsequent subsections begin with a focus on the elements of a
generic routing process that is used to establish routing assets and
points of access to the routing functionality. Next, the
<xref target="ISO.7498-2.1988"/>
security model is briefly described. Then, consideration is given to
issues specific to or amplified in LLNs. This section concludes with the
formulation of a set of security objectives for ROLL.</t>
<section anchor="routing-assets"
title="Routing Assets and Points of Access">
<t>An asset is an important system resource (including information,
process, or physical resource), the access to, corruption or loss of
which adversely affects the system. In the control plane context, an
asset is information about the network, processes used to manage and
manipulate this data, and the physical devices on which this data is
stored and manipulated. The corruption or loss of these assets may
adversely impact the control plane of the network. Within the same
context, a point of access is an interface or protocol that
facilitates interaction between control plane components. Identifying
these assets and points of access will provide a basis for enumerating
the attack surface of the control plane.</t>
<t>A level-0 data flow diagram <xref target="Yourdon1979"/> is used
here to identify the assets and points of access within a generic
routing process. The use of a data flow diagram allows for a clear and
concise model of the way in which routing nodes interact and process
information, and hence provides a context for threats and attacks. The
goal of the model is to be as detailed as possible so that
corresponding assets, points of access, and process in an individual
routing protocol can be readily identified.</t>
<t><xref target="Fig1"/> shows that nodes participating in the routing
process transmit messages to discover neighbors and to exchange
routing information; routes are then generated and stored, which may
be maintained in the form of the protocol forwarding table. The nodes
use the derived routes for making forwarding decisions.</t>
<figure align="center" anchor="Fig1"
title="Data Flow Diagram of a Generic Routing Process">
<preamble/>
<artwork align="left">
<![CDATA[
...................................................
: :
: :
|Node_i|<------->(Routing Neighbor _________________ :
: Discovery)------------>Neighbor Topology :
: -------+--------- :
: | :
|Node_j|<------->(Route/Topology +--------+ :
: Exchange) | :
: | V ______ :
: +---->(Route Generation)--->Routes :
: ---+-- :
: | :
: Routing on a Node Node_k | :
...................................................
|
|Forwarding |
|On Node_l|<-------------------------------------------+
Notation:
(Proc) A process Proc
________
topology A structure storing neighbor adjacency (parent/child)
--------
________
routes A structure storing the forwarding information base (FIB)
--------
|Node_n| An external entity Node_n
-------> Data flow
]]>
</artwork>
<postamble/>
</figure>
<t>It is seen from <xref target="Fig1"/> that <list style="symbols">
<t>Assets include<list style="symbols">
<t>routing and/or topology information;</t>
<t>route generation process;</t>
<t>communication channel resources (bandwidth);</t>
<t>node resources (computing capacity, memory, and remaining
energy);</t>
<t>node identifiers (including node identity and ascribed
attributes such as relative or absolute node location).</t>
</list></t>
<t>Points of access include<list style="symbols">
<t>neighbor discovery;</t>
<t>route/topology exchange;</t>
<t>node physical interfaces (including access to data
storage).</t>
</list></t>
</list>A focus on the above list of assets and points of access
enables a more directed assessment of routing security; for example,
it is readily understood that some routing attacks are in the form of
attempts to misrepresent routing topology. Indeed, the intention of
the security threat analysis is to be comprehensive. Hence, some of
the discussion which follows is associated with assets and points of
access that are not directly related to routing protocol design but
nonetheless provided for reference since they do have direct
consequences on the security of routing.</t>
</section>
<section anchor="iso" title="The ISO 7498-2 Security Reference Model">
<t>At the conceptual level, security within an information system in
general and applied to ROLL in particular is concerned with the
primary issues of authentication, access control, data
confidentiality, data integrity, and non-repudiation. In the context
of ROLL</t>
<t><list hangIndent="6" style="hanging">
<t hangText="Authentication"><vspace/>Authentication involves the
mutual authentication of the routing peers prior to exchanging
route information (i.e., peer authentication) as well as ensuring
that the source of the route data is from the peer (i.e., data
origin authentication).
<xref target="RFC5548" /> points out that LLNs can be drained by
unauthenticated peers before configuration.
<xref target="RFC5673" /> requires
availability of open and untrusted side channels for new joiners,
and it requires strong and automated authentication so that
networks can automatically accept or reject new joiners.</t>
<t hangText="Access Control"><vspace/>Access Control provides
protection against unauthorized use of the asset, and deals with the
authorization of a node.</t>
<t hangText="Confidentiality"><vspace/>Confidentiality involves
the protection of routing information as well as routing neighbor
maintenance exchanges so that only authorized and intended network
entities may view or access it. Because LLNs are most commonly
found on a publicly accessible shared medium, e.g., air or wiring
in a building, and sometimes formed ad hoc, confidentiality also
extends to the neighbor state and database information within the
routing device since the deployment of the network creates the
potential for unauthorized access to the physical devices
themselves.</t>
<t hangText="Integrity"><vspace/>Integrity entails the protection
of routing information and routing neighbor maintenance exchanges,
as well as derived information maintained in the database, from
unauthorized modification, insertions, deletions or replays. to be
addressed beyond the routing protocol.</t>
<t hangText="Non-repudiation"><vspace/>Non-repudiation is the
assurance that the transmission and/or reception of a message
cannot later be denied. The service of non-repudiation applies
after-the-fact and thus relies on the logging or other capture of
on-going message exchanges and signatures. Applied to routing,
non-repudiation is not an issue because it does not apply to
routing protocols, which are machine-to-machine protocols.
Further, with the LLN application domains as described in
<xref target="RFC5867" /> and
<xref target="RFC5548" />,
proactive measures are much more
critical than retrospective protections. Finally, given the
significant practical limits to on-going routing transaction
logging and storage and individual device digital signature
verification for each exchange, non-repudiation in the context of
routing is an unsupportable burden that bears no further
considered as a ROLL security issue.</t>
</list></t>
<t>It is recognized that, besides those security issues captured in
the ISO 7498-2 model, availability, is a security requirement:<list
hangIndent="6" style="hanging">
<t hangText="Availability"><vspace/>Availability ensures that
routing information exchanges and forwarding services need to be
available when they are required for the functioning of the
serving network. Availability will apply to maintaining efficient
and correct operation of routing and neighbor discovery exchanges
(including needed information) and forwarding services so as not
to impair or limit the network's central traffic flow function</t>
</list></t>
<t>It should be emphasized here that for ROLL security the above
requirements must be complemented by the proper security policies and
enforcement mechanisms to ensure that security objectives are met by a
given ROLL implementation.</t>
</section>
<section anchor="roll-issues"
title="Issues Specific to or Amplified in LLNs">
<t>The work <xref target="RFC5548"/>, <xref target="RFC5673"/>, <xref
target="RFC5826"/>, and <xref target="RFC5867"/> have identified
specific issues and constraints of routing in LLNs for the urban,
industrial, home automation, and building automation application
domains, respectively. The following is a list of observations and
evaluation of their impact on routing security considerations.</t>
<t><list hangIndent="6" style="hanging">
<t
hangText="Limited energy, memory, and processing node resources"><vspace/>As
a consequence of these constraints, there is an even more critical
need than usual for a careful study of trade-offs on which and
what level of security services are to be afforded during the
system design process. The chosen security mechanisms also needs
to work within these constraints. Synchronization of security
states with sleepy nodes is yet another issue.</t>
<t hangText="Large scale of rolled out network"><vspace/>The
possibly numerous nodes to be deployed make manual on-site
configuration unlikely. For example, an urban deployment
can see several hundreds of thousands of nodes being installed
by many installers with a low level of expertise.
Nodes may be installed and not activated for many years,
and additional nodes may be added later on, which may be
from old inventory. The lifetime of the network is measured in
decades, and this complicates the operation of key management.</t>
<t hangText="Autonomous operations"><vspace/>Self-forming and
self-organizing are commonly prescribed requirements of LLNs. In
other words, a routing protocol designed for LLNs needs to contain
elements of ad hoc networking and in most cases cannot rely on
manual configuration for initialization or local filtering rules.
Network topology/ownership changes, partitioning or merging, as
well as node replacement, can all contribute to complicating the
operations of key management.</t>
<t hangText="Highly directional traffic"><vspace/>Some types of
LLNs see a high percentage of their total traffic traverse between
the nodes and the LLN Border Routers (LBRs) where the LLNs connect
to non-LLNs. The special routing status of and the greater volume
of traffic near the LBRs have routing security consequences as a
higher valued attack target. In fact, when Point-to-MultiPoint
(P2MP) and MultiPoint-to-Point (MP2P) traffic represents a
majority of the traffic, routing attacks consisting of advertising
incorrect preferred routes can cause serious damage.</t>
<t>
While it might seem that nodes higher up in the cyclic graph (i.e. those
with lower rank) should be secured in a stronger fashion, it is not
in general easy to predict which nodes will occupy those positions
until after deployment. Issues of redundancy and inventory control
suggests that any node might wind up in such a sensitive attack position,
so all nodes need to be equally secure.</t>
<t>In addition, even if it were possible to predict which nodes will
occupy positions of lower rank and provision them with stronger
security mechanisms, in the absense of a strong authorization model,
any node could advertise an incorrect preferred route.</t>
<t hangText="Unattended locations and limited physical security"><vspace/>Many
applications have the nodes deployed in unattended or remote
locations; furthermore, the nodes themselves are often built with
minimal physical protection. These constraints lower the barrier
of accessing the data or security material stored on the nodes
through physical means.</t>
<t hangText="Support for mobility"><vspace/>On the one hand, only
a limited number of applications require the support of mobile nodes,
e.g., a home LLN that includes nodes on wearable health care
devices or an industry LLN that includes nodes on cranes and
vehicles. On the other hand, if a routing protocol is indeed used
in such applications, it will clearly need to have corresponding
security mechanisms.</t>
<t>Additionally nodes may appear to move from one side of a wall
to another without any actual motion involved, the result of changes
to electromagnetic properties, such as opening and closing of a
metal door. </t>
<t hangText="Support for multicast and anycast"><vspace/>Support
for multicast and anycast is called out chiefly for large-scale
networks. Since application of these routing mechanisms in
autonomous operations of many nodes is new, the consequence on
security requires careful consideration.</t>
</list></t>
<t>The above list considers how an LLN's physical constraints, size,
operations, and variety of application areas may impact security.
However, it is the combinations of these factors that particularly
stress the security concerns. For instance, securing routing for a
large number of autonomous devices that are left in unattended
locations with limited physical security presents challenges that are
not found in the common circumstance of administered networked
routers. The following subsection sets up the security objectives for
the routing protocol designed by the ROLL WG.</t>
</section>
<section anchor="roll-objs" title="ROLL Security Objectives">
<t>This subsection applies the ISO 7498-2 model to routing assets and
access points, taking into account the LLN issues, to develop a set of
ROLL security objectives.</t>
<t>Since the fundamental function of a routing protocol is to build
routes for forwarding packets, it is essential to ensure that:
<list style="symbols">
<t>routing/topology information iintegrity remains intact during
transfer and in storage;</t>
<t>routing/topology information is used by authorized
entities;</t>
<t>routing/topology information is available when needed.</t>
</list>
In conjunction, it is necessary to be assured that
<list style="symbols">
<t>authorized peers authenticate themselves during the routing
neighbor discovery process;</t>
<t>the routing/topology information received is generated
according to the protocol design.</t>
</list>
However, when trust cannot be fully vested through
authentication of the principals alone, i.e., concerns of insider
attack, assurance of the truthfulness and timeliness of the received
routing/topology information is necessary. With regard to
confidentiality, protecting the routing/topology information from
unauthorized exposure may be desirable in certain cases but is in
itself less pertinent in general to the routing function.</t>
<t>One of the main problems of synchronizing security states of sleepy
nodes, as listed in the last subsection, lies in difficulties in
authentication; these nodes may not have received in time the most
recent update of security material. Similarly, the issues of minimal
manual configuration, prolonged rollout and delayed addition of nodes,
and network topology changes also complicate key management. Hence,
routing in LLNs needs to bootstrap the authentication process and
allow for flexible expiration scheme of authentication
credentials.</t>
<t>The vulnerability brought forth by some special-function nodes,
e.g., LBRs, requires the assurance, particularly in a security
context,
<list style="symbols">
<t>of the availability of communication channels and node
resources;</t>
<t>that the neighbor discovery process operates without
undermining routing availability.</t>
</list></t>
<t>There are other factors which are not part of a ROLL protocol but
directly affecting its function. These factors include weaker barrier
of accessing the data or security material stored on the nodes through
physical means; therefore, the internal and external interfaces of a
node need to be adequate for guarding the integrity, and possibly the
confidentiality, of stored information, as well as the integrity of
routing and route generation processes.</t>
<t>Each individual system's use and environment will dictate how the
above objectives are applied, including the choices of security
services as well as the strengths of the mechanisms that must be
implemented. The next two sections take a closer look at how the ROLL
security objectives may be compromised and how those potential
compromises can be countered.</t>
</section>
</section>
<section anchor="threat-sources" title="Threat Sources">
<t><xref target="RFC4593" /> provides a detailed review of the threat
sources: outsiders and byzantine. ROLL has the same threat
sources.</t>
</section>
<section anchor="roll-threats" title="Threats and Attacks">
<t>This section outlines general categories of threats under the ISO
7498-2 model and highlights the specific attacks in each of these
categories for ROLL. As defined in <xref target="RFC4949"/>, a threat is
"a potential for violation of security, which exists when there is a
circumstance, capability, action, or event that could breach security
and cause harm."</t>
<t>An attack is "an assault on system security that
derives from an intelligent threat, i.e., an intelligent act that is a
deliberate attempt (especially in the sense of a method or technique) to
evade security services and violate the security policy of a
system."
</t>
<t>The subsequent subsections consider the threats and the attacks that
can cause security breaches under the ISO 7498-2 model to the routing
assets and via the routing points of access identified in <xref
target="routing-assets"/>. The assessment steps through the security
concerns of each routing asset and looks at the attacks that can exploit
routing points of access. The threats and attacks identified are based
on the routing model analysis and associated review of the existing
literature. The source of the attacks is assumed to be from either
inside or outside attackers. The capability these attackes may be
limited to node-equivalent, but also to more sophisticated
computing platforms.</t>
<section anchor="authorization-threat"
title="Threats due to failures to Authenticate">
<section anchor="any-identity" title="Node Impersonation">
<t>If an attacker can join a network with any identify,
then it may be able to assume the role of a legitimate
(and existing node). It may be able to report false readings
(in metering applications), or provide inappropriate control
messages (in control systems involving actuators) if the
security of the application is leveraged from the security
of the routing system.</t>
<t>In other systems where there is separate application layer
security, the ability to impersonate a node would permit an attacker
to direct traffic to itself, which facilitates on-path attacks
including replaying, delaying, or duplicating control messages.
</t>
</section>
<section anchor="extra-node" title="Dummy Node">
<t>If an attacker can join a network with any identify,
then it can pretend to be a legitimate node, receiving any
service legitimate nodes receive. It may also be able to report false
readings (in metering applications),
or provide inappropriate authorizations (in control systems involving
actuators), or perform any other attacks that are facilitated
by being able to direct traffic towards itself.
</t>
</section>
<section anchor="spam-resource" title="Node Resource Spam">
<t>If an attacker can join a network with any identify,
then it can continously do so, draining down the resources of
the network to store identity and routing information, potentionally
forcing legitimate nodes of the network.</t>
</section>
</section>
<section anchor="confident-threat"
title="Threats and Attacks on Confidentiality">
<t>The assessment in <xref target="iso"/> indicates that there are
threat actions against the confidentiality of routing information at
all points of access. The confidentiality threat consequences is
disclosure, see Section 3.1.2 of <xref target="RFC4593"/>. For ROLL
this is the disclosure of routing information either by evesdropping
on the communication exchanges between routing nodes or by direct
access of node's information.</t>
<section anchor="route-exch-expo" title="Routing Exchange Exposure">
<t>Routing exchanges include both routing information as well as
information associated with the establishment and maintenance of
neighbor state information. As indicated in <xref
target="routing-assets"/>, the associated routing information assets
may also include device specific resource information, such as
memory, remaining power, etc., that may be metrics of the routing
protocol.</t>
<t>The routing exchanges will contain
reachability information, which would identify the relative
importance of different nodes in the network. Nodes higher up in
the DODAG, to which more streams of information flow, would be more
interesting targets for other attacks, and routing exchange
exposures can identify them.
</t>
</section>
<section anchor="route-info-expo"
title="Routing Information (Routes and Network Topology) Exposure">
<t>Routes (which may be maintained in the form of the protocol
forwarding table) and neighbor topology information are the products
of the routing process that are stored within the node device
databases.</t>
<t>The exposure of this information will allow attachers to gain
direct access to the configuration and connectivity of the network
thereby exposing routing to targeted attacks on key nodes or links.
Since routes and neighbor topology information is stored within the
node device, threats or attacks on the confidentiality of the
information will apply to the physical device including specified
and unspecified internal and external interfaces.</t>
<t>The forms of attack that allow unauthorized access or disclosure
of the routing information (other than occurring through explicit
node exchanges) will include:
<list style="symbols">
<t>Physical device compromise;</t>
<t>Remote device access attacks (including those occurring
through remote network management or software/field upgrade
interfaces).</t>
</list>
</t>
<t>Both of these attack vectors are considered a device specific issue, and are
out of scope for the RPL protocol to defend against. In some applications,
physical device compromise may be a real threat and it may be necessary to
provide for other devices to react quickly to exclude a compromised device.
</t>
</section>
</section>
</section>
<section anchor="integ-threat" title="Threats and Attacks on Integrity">
<t>The assessment in <xref target="iso"/> indicates that information
and identity assets are exposed to integrity threats from all points
of access. In other words, the integrity threat space is defined by
the potential for exploitation introduced by access to assets
available through routing exchanges and the on-device storage.</t>
<section anchor="manipul" title="Routing Information Manipulation">
<t>
Manipulation of routing information that range from neighbor
states to derived routes will allow unauthorized sources to
influence the operation and convergence of the routing protocols and
ultimately impact the forwarding decisions made in the network.
</t>
<t>
Manipulation of topology and reachability information will allow
unauthorized sources to influence the nodes with which routing
information is exchanged and updated. The consequence of
manipulating routing exchanges can thus lead to sub-optimality and
fragmentation or partitioning of the network by restricting the
universe of routers with which associations can be established and
maintained.
</t>
<t>A sub-optimal network may use too much power and/or may congest some
routes leading to premature failure of a node, and a denial of service
on the entire network.
</t>
<t>In addition, being able to attract network traffic can
make a blackhole attack more damaging.
</t>
<t>The forms of attack that allow manipulation to compromise the
content and validity of routing information include<list
style="symbols">
<t>Falsification, including overclaiming and misclaiming;</t>
<t>Routing information replay;</t>
<t>Byzantine (internal) attacks that permit corruption of
routing information in the node even where the node continues to
be a validated entity within the network (see, for example,
<xref target="RFC4593"/> for further discussions on Byzantine
attacks);</t>
<t>Physical device compromise or remote device access
attacks.</t>
</list></t>
</section>
<section anchor="id-misappr" title="Node Identity Misappropriation">
<t>
Falsification or misappropriation of node identity between
routing participants opens the door for other attacks; it can also
cause incorrect routing relationships to form and/or topologies to
emerge. Routing attacks may also be mounted through less
sophisticated node identity misappropriation in which the valid
information broadcast or exchanged by a node is replayed without
modification. The receipt of seemingly valid information that is
however no longer current can result in routing disruption, and
instability (including failure to converge). Without measures to
authenticate the routing participants and to ensure the freshness
and validity of the received information the protocol operation can
be compromised. The forms of attack that misuse node identity
include<list style="symbols">
<t>Identity attacks, including Sybil attacks in which a
malicious node illegitimately assumes multiple identities;</t>
<t>Routing information replay.</t>
</list></t>
</section>
</section>
<section anchor="avail-threat"
title="Threats and Attacks on Availability">
<t>The assessment in <xref target="iso"/> indicates that the process
and resources assets are exposed to threats against availability;
attacks in this category may exploit directly or indirectly
information exchange or forwarding (see <xref target="RFC4732"/> for a
general discussion).</t>
<section anchor="route-exch-intrpt"
title="Routing Exchange Interference or Disruption">
<t>Interference is the threat action and disruption is threat
consequence that allows attackers to influence the operation and
convergence of the routing protocols by impeding the routing
information exchange.</t>
<t>The forms of attack that allow interference or disruption of
routing exchange include:<list style="symbols">
<t>Routing information replay;</t>
<t>ACK spoofing;</t>
<t><xref target="overload-attack">Overload attacks.</xref></t>
</list></t>
<t>In addition, attacks may also be directly conducted at the
physical layer in the form of jamming or interfering.</t>
</section>
<section anchor="disrupt-forward"
title="Network Traffic Forwarding Disruption">
<t>The disruption of the network traffic forwarding capability will
undermine the central function of network routers and the ability to
handle user traffic. This affects the availability of the network
because of the potential to impair the primary capability of the
network.</t>
<t>In addition to physical layer obstructions, the forms of attack
that allows disruption of network traffic forwarding include <xref
target="Karlof2003"/><list style="symbols">
<t>Selective forwarding attacks;
<figure align="center" anchor="Fig2"
title="Selective Forwarding">
<preamble/>
<artwork align="left">
<![CDATA[
|Node_1|--(msg1|msg2|msg3)-->|Attacker|--(msg1|msg3)-->|Node_2|
(a) Selective Forwarding
]]> </artwork>
<postamble/>
</figure>
</t>
<t>Wormhole attacks;
<figure align="center" anchor="Fig3"
title="Wormhole Attacks">
<preamble/>
<artwork align="left">
<![CDATA[
|Node_1|-------------Unreachable---------x|Node_2|
| ^
| Private Link |
'-->|Attacker_1|===========>|Attacker_2|--'
(b) Wormhole
]]> </artwork>
<postamble/>
</figure>
</t>
<t>Sinkhole attacks.
<figure align="center" anchor="Fig4"
title="Selective Forwarding, Wormhole, and Sinkhole Attacks">
<preamble/>
<artwork align="left">
<![CDATA[
|Node_1| |Node_4|
| |
`--------. |
Falsify as \ |
Good Link \ | |
To Node_5 \ | |
\ V V
|Node_2|-->|Attacker|--Not Forwarded---x|Node_5|
^ ^ \
| | \ Falsify as
| | \Good Link
/ | To Node_5
,-------' |
| |
|Node_3| |Node_i|
(c) Sinkhole
]]> </artwork>
<postamble/>
</figure>
</t>
</list></t>
<t>
These attacks are generally done to both control plane and forwarding plane traffic.
A system that prevents control plane traffic (RPL messages) from being diverted in these ways will also
prevent actual data from being diverted.
</t>
</section>
<section anchor="disrpt-comm-resourse"
title="Communications Resource Disruption">
<t>Attacks mounted against the communication channel resource assets
needed by the routing protocol can be used as a means of disrupting
its operation. However, while various forms of Denial of Service
(DoS) attacks on the underlying transport subsystem will affect
routing protocol exchanges and operation (for example physical layer
RF jamming in a wireless network or link layer attacks), these
attacks cannot be countered by the routing protocol. As such, the
threats to the underlying transport network that supports routing is
considered beyond the scope of the current document. Nonetheless,
attacks on the subsystem will affect routing operation and so must
be directly addressed within the underlying subsystem and its
implemented protocol layers.</t>
</section>
<section anchor="exhaust-resource" title="Node Resource Exhaustion">
<t>A potential threat consequence can arise from attempts to
overload the node resource asset by initiating exchanges that can
lead to the exhaustion of processing, memory, or energy resources.
The establishment and maintenance of routing neighbors opens the
routing process to engagement and potential acceptance of multiple
neighboring peers. Association information must be stored for each
peer entity and for the wireless network operation provisions made
to periodically update and reassess the associations. An introduced
proliferation of apparent routing peers can therefore have a
negative impact on node resources.</t>
<t>Node resources may also be unduly consumed by attackers
attempting uncontrolled topology peering or routing exchanges,
routing replays, or the generating of other data traffic floods.
Beyond the disruption of communications channel resources, these
consequences may be able to exhaust node resources only where the
engagements are able to proceed with the peer routing entities.
Routing operation and network forwarding functions can thus be
adversely impacted by node resources exhaustion that stems from
attacks that include:<list style="symbols">
<t>Identity (including Sybil) attacks;</t>
<t>Routing information replay attacks;</t>
<t>HELLO flood attacks;</t>
<t><xref target="overload-attack">Overload attacks.</xref></t>
</list></t>
</section>
</section>
<section anchor="counter-measur" title="Countermeasures">
<t>By recognizing the characteristics of LLNs that may impact routing,
this analysis provides the basis for developing capabilities within ROLL
protocols to deter the identified attacks and mitigate the threats. The
following subsections consider such countermeasures by grouping the
attacks according to the classification of the ISO 7498-2 model so that
associations with the necessary security services are more readily
visible. However, the considerations here are more systematic than
confined to means available only within routing; the next section will
then distill and make recommendations appropriate for a secured ROLL
protocol.</t>
<section anchor="counter-confident-atk"
title="Confidentiality Attack Countermeasures">
<t>Attacks to disclosure routing information may be mounted at the
level of the routing information assets, at the points of access
associated with routing exchanges between nodes, or through device
interface access. To gain access to routing/topology information, the
attacker may rely on a compromised node that deliberately exposes the
information during the routing exchange process, may rely on passive
wiretapping or traffic analysis, or may attempt access through a
component or device interface of a tampered routing node.</t>
<section title="Countering Deliberate Exposure Attacks">
<t>A deliberate exposure attack is one in which an entity that is
party to the routing process or topology exchange allows the
routing/topology information or generated route information to be
exposed to an unauthorized entity.</t>
<t>A prerequisite to countering this attack is to ensure that the
communicating nodes are authenticated prior to data encryption
applied in the routing exchange. Authentication ensures that the
nodes are who they claim to be even though it does not provide an
indication of whether the node has been compromised.</t>
<t>To mitigate the risk of deliberate exposure, the process that
communicating nodes use to establish session keys must be
peer-to-peer (i.e., between the routing initiating and responding
nodes). This helps ensure that neither node is exchaning routing
information with another peer without the knowledge of both
communicating peerscan. For a deliberate exposure attack to succeed,
the comprised node will need to more overt and take independent
actions in order to disclose the routing information to 3rd
party.</t>
<t>Note that the same measures which apply to securing
routing/topology exchanges between operational nodes must also
extend to field tools and other devices used in a deployed network
where such devices can be configured to participate in routing
exchanges.</t>
</section>
<section title="Countering Passive Wiretapping Attacks">
<t>A passive wiretap attack seeks to breach routing confidentiality through
passive, direct analysis and processing of the information exchanges
between nodes. </t>
<t>Passive wiretap attacks can be directly countered through the use of
data encryption for all routing exchanges. Only when a validated and
authenticated node association is completed will routing exchange be
allowed to proceed using established session keys and an agreed
encryption algorithm. The strength of the encryption algorithm and
session key sizes will determine the minimum requirement for an
attacker mounting this passive security attack. The possibility of
incorporating options for security level and algorithms is further
considered in <xref target="match-needs"/>. Because of the resource
constraints of LLN devices, symmetric (private) key encryption will
provide the best trade-off in terms of node and channel resource
overhead and the level of security achieved. This will of course not
preclude the use of asymmetric (public) key encryption during the
session key establishment phase.</t>
<t>As with the key establishment process, data encryption must
include an authentication prerequisite to ensure that each node is
implementing a level of security that prevents deliberate or
inadvertent exposure. The authenticated key establishment will
ensure that confidentiality is not compromised by providing the
information to an unauthorized entity (see also <xref
target="Huang2003"/>).</t>
<t>Based on the current state of the art, a minimum 128-bit key
length should be applied where robust confidentiality is demanded
for routing protection. This session key shall be applied in
conjunction with an encryption algorithm that has been publicly
vetted and where applicable approved for the level of security
desired. Algorithms such as the Advanced Encryption Standard (AES)
<xref target="FIPS197"/>, adopted by the U.S. government, or
Kasumi-Misty <xref target="Kasumi3gpp"/>, adopted by the 3GPP 3rd
generation wireless mobile consortium, are examples of symmetric-key
algorithms capable of ensuring robust confidentiality for routing
exchanges. The key length, algorithm and mode of operation will be
selected as part of the overall security trade-off that also
achieves a balance with the level of confidentiality afforded by the
physical device in protecting the routing assets.</t>
<t>As with any encryption algorithm, the use of ciphering
synchronization parameters and limitations to the usage duration of
established keys should be part of the security specification to
reduce the potential for brute force analysis.</t>
</section>
<section title="Countering Traffic Analysis">
<t>Traffic analysis provides an indirect means of subverting
confidentiality and gaining access to routing information by
allowing an attacker to indirectly map the connectivity or flow
patterns (including link-load) of the network from which other
attacks can be mounted. The traffic analysis attack on an LLN,
especially one founded on shared medium, is passive and relies on
the ability to read the immutable source/destination layer-3 routing
information that must remain unencrypted to permit network routing.
</t>
<t>One way in which passive traffic analysis attacks can be muted is
through the support of load balancing that allows traffic to a given
destination to be sent along diverse routing paths. Where the
routing protocol supports load balancing along multiple links at
each node, the number of routing permutations in a wide area network
surges thus increasing the cost of traffic analysis.
ROLL does not generally support multi-path routing within a
single DODAG. Multiple DODAGs are supported in the protocol,
but few deployments will have space for more than half a dozen,
and there are at present no clear ways to multiplex traffic
for a single application across multiple DODAGs.
</t>
<t>
Another approach to countering
passive traffic analysis could be for nodes to maintain constant
amount of traffic to different destinations through the generation
of arbitrary traffic flows; the drawback of course would be the
consequent overhead. </t>
<t>The only means of fully countering a traffic analysis attack is
through the use of tunneling (encapsulation) where encryption is
applied across the entirety of the original packet
source/destination addresses. Deployments which use layer-2
security that includes encryption already do this for all traffic.
</t>
</section>
<section anchor="counter-remote"
title="Countering Remote Device Access Attacks">
<t>Where LLN nodes are deployed in the field, measures are
introduced to allow for remote retrieval of routing data and for
software or field upgrades. These paths create the potential for a
device to be remotely accessed across the network or through a
provided field tool. In the case of network management a node can be
directly requested to provide routing tables and neighbor
information.</t>
<t>To ensure confidentiality of the node routing information against
attacks through remote access, any local or remote device requesting
routing information must be authenticated to ensure authorized
access. Since remote access is not invoked as part of a routing
protocol security of routing information stored on the node against
remote access will not be addressable as part of the routing
protocol.</t>
</section>
</section>
<section anchor="counter-integ-atk"
title="Integrity Attack Countermeasures">
<t>Integrity attack countermeasures address routing information
manipulation, as well as node identity and routing information misuse.
Manipulation can occur in the form of falsification attack and
physical compromise. To be effective, the following development
considers the two aspects of falsification, namely, the unauthorized
modifications and the overclaiming and misclaiming content. The
countering of physical compromise was considered in the previous
section and is not repeated here. With regard to misuse, there are two
types of attacks to be deterred, identity attacks and replay
attacks.</t>
<section title="Countering Unauthorized Modification Attacks">
<t>Unauthorized modifications may occur in the form of altering the
message being transferred or the data stored. Therefore, it is
necessary to ensure that only authorized nodes can change the
portion of the information that is allowed to be mutable, while the
integrity of the rest of the information is protected, e.g., through
well-studied cryptographic mechanisms.</t>
<t>Unauthorized modifications may also occur in the form of
insertion or deletion of messages during protocol changes.
Therefore, the protocol needs to ensure the integrity of the
sequence of the exchange sequence.</t>
<t>The countermeasure to unauthorized modifications needs to:
<list style="symbols">
<t>implement access control on storage;</t>
<t>provide data integrity service to transferred messages and
stored data;</t>
<t>include sequence number under integrity protection.</t>
</list>
</t>
</section>
<section title="Countering Overclaiming and Misclaiming Attacks">
<t>Both overclaiming and misclaiming aim to introduce false routes
or topology that would not be generated by the network otherwise,
while there are not necessarily unauthorized modifications to the
routing messages or information. The requisite for a counter is the
capability to determine unreasonable routes or topology.</t>
<t>The counter to overclaiming and misclaiming may employ:
<list style="symbols">
<t>comparison with historical routing/topology data;</t>
<t>designs which restrict realizable network topologies.</t>
</list>
</t>
</section>
<section anchor="counter-sybil"
title="Countering Identity (including Sybil) Attacks">
<t>Identity attacks, sometimes simply called spoofing, seek to gain
or damage assets whose access is controlled through identity. In
routing, an identity attacker can illegitimately participate in
routing exchanges, distribute false routing information, or cause an
invalid outcome of a routing process.</t>
<t>A perpetrator of Sybil attacks assumes multiple identities. The
result is not only an amplification of the damage to routing, but
extension to new areas, e.g., where geographic distribution is
explicitly or implicitly an asset to an application running on the
LLN, for example, the LBR in a P2MP or MP2P LLN.</t>
</section>
<section anchor="counter-replay"
title="Countering Routing Information Replay Attacks">
<t>In many routing protocols, message replay can result in false topology and/or
routes. This is often counted with some kind of counter to ensure the freshness
of the message. Replay of a current, literal RPL message are in general idempotent
to the topology. An older (lower DODAGVersionNumber) message, if replayed
would be rejected as being stale. The trickle algorithm further dampens the
affect of any such replay, as if the message was current, then it would contain
the same information as before, and it would cause no network changes.
</t>
<t>Replays may well occur in some radio technologies (not very likely, 802.15.4) as
a result of echos or reflections, and so some replays must be assumed to occur naturally.
</t>
<t>Note that for there to be no affect at all, the replay must be done with the
same apparent power for all nodes receiving the replay. A change in apparent power
might change the metrics through changes to the ETX and therefore might affect the routing even
though the contents of the packet were never changed. Any replay which appears to
be different should be analyzed as a Selective Forwarding Attack, Sinkhole Attack or
Wormhole Attack.
</t>
</section>
<section anchor="counter-byzantine"
title="Countering Byzantine Routing Information Attacks">
<t>Where a node is captured or compromised but continues to operate
for a period with valid network security credentials, the potential
exists for routing information to be manipulated. This compromise of
the routing information could thus exist in spite of security
countermeasures that operate between the peer routing devices.</t>
<t>Consistent with the end-to-end principle of communications, such
an attack can only be fully addressed through measures operating
directly between the routing entities themselves or by means of
external entities able to access and independently analyze the
routing information. Verification of the authenticity and liveliness
of the routing entities can therefore only provide a limited counter
against internal (Byzantine) node attacks.</t>
<t>For link state routing protocols where information is flooded
with, for example, areas (OSPF <xref target="RFC2328"/>) or levels
(ISIS <xref target="RFC1142"/>), countermeasures can be directly
applied by the routing entities through the processing and
comparison of link state information received from different peers.
By comparing the link information from multiple sources decisions
can be made by a routing node or external entity with regard to
routing information validity; see Chapter 2 of <xref
target="Perlman1988"/> for a discussion on flooding attacks.</t>
<t>For distance vector protocols where information is aggregated at
each routing node it is not possible for nodes to directly detect
Byzantine information manipulation attacks from the routing
information exchange. In such cases, the routing protocol must
include and support indirect communications exchanges between
non-adjacent routing peers to provide a secondary channel for
performing routing information validation. S-RIP <xref
target="Wan2004"/> is an example of the implementation of this type
of dedicated routing protocol security where the correctness of
aggregate distance vector information can only be validated by
initiating confirmation exchanges directly between nodes that are
not routing neighbors.</t>
<t>Alternatively, an entity external to the routing protocol would
be required to collect and audit routing information exchanges to
detect the Byzantine attack. In the context of the current security
analysis, any protection against Byzantine routing information
attacks will need to be directly included within the mechanisms of
the ROLL routing protocol.
</t>
</section>
</section>
<section anchor="counter-avail-atk"
title="Availability Attack Countermeasures">
<t>As alluded to before, availability requires that routing
information exchanges and forwarding mechanisms be available when
needed so as to guarantee proper functioning of the network. This may,
e.g., include the correct operation of routing information and
neighbor state information exchanges, among others. We will highlight
the key features of the security threats along with typical
countermeasures to prevent or at least mitigate them. We will also
note that an availability attack may be facilitated by an identity
attack as well as a replay attack, as was addressed in <xref
target="counter-sybil"/> and <xref target="counter-replay"/>,
respectively.</t>
<section title="Countering HELLO Flood Attacks and ACK Spoofing Attacks">
<t>HELLO Flood <xref target="Karlof2003"/>,<xref
target="I-D.suhopark-hello-wsn"/> and ACK Spoofing attacks are
different but highly related forms of attacking an LLN. They
essentially lead nodes to believe that suitable routes are available
even though they are not and hence constitute a serious availability
attack.</t>
<t>A HELLO attack mounted against RPL would involve sending out
(or replaying) DIO messages by the attacker. Lower power LLN nodes
might then attempt to join the DODAG at a lower rank than they would
otherwise.
</t>
<t>The most effective method from <xref target="I-D.suhopark-hello-wsn"/>
is the verify bidirectionality. A number of layer-2 links are arranged
in controller/spoke arrangements, and continuously are validating connectivity
at layer 2.</t>
<t>In addition, in order to calculate metrics, the ETX must be computed,
and this involves, in general, sending a number of messages between nodes
which are believed to be adjacent. <xref target="I-D.kelsey-intarea-mesh-link-establishment"/>
is one such protocol.
</t>
<t>In order to join the DODAG, a DAO message is sent upwards.
In RPL the DAO is acknowledged by the DAO-ACK message. This clearly
checks bidirectionality at the control plane.
</t>
<t>As discussed in section 5.1, <xref target="I-D.suhopark-hello-wsn"/>
a receiver with a sensitive receiver could well hear the DAOs, and even
send DAO-ACKs as well. Such a node is a form of WormHole attack.
</t>
<t>
These attacks are also all easily defended against using either layer-2
or layer-3 authentication. Such an attack could only be made against
a completely open network (such as might be used for provisioning new nodes),
or by a compromised node.
</t>
</section>
<section anchor="overload-attack" title="Countering Overload Attacks">
<t>Overload attacks are a form of DoS attack in that a malicious
node overloads the network with irrelevant traffic, thereby draining
the nodes' energy store more quickly, when the nodes rely on
batteries or energy scavenging. It thus significantly shortens the
lifetime of networks of energy-constrained nodes and constitutes
another serious availability attack.</t>
<t>With energy being one of the most precious assets of LLNs,
targeting its availability is a fairly obvious attack. Another way
of depleting the energy of an LLN node is to have the malicious node
overload the network with irrelevant traffic. This impacts
availability since certain routes get congested which:
<list style="symbols">
<t>renders them useless for affected nodes and data can hence
not be delivered;</t>
<t>makes routes longer as shortest path algorithms work with the
congested network;</t>
<t>depletes battery and energy scavenging nodes more quickly and thus
shortens the network's availability at large.</t>
</list>
</t>
<t>Overload attacks can be countered by deploying a series of
mutually non-exclusive security measures:
<list style="symbols">
<t>introduce quotas on the traffic rate each node is allowed to
send;</t>
<t>isolate nodes which send traffic above a certain threshold
based on system operation characteristics;</t>
<t>allow only trusted data to be received and forwarded.</t>
</list>
</t>
<t>As for the first one, a simple approach to minimize the harmful
impact of an overload attack is to introduce traffic quotas. This
prevents a malicious node from injecting a large amount of traffic
into the network, even though it does not prevent said node from
injecting irrelevant traffic at all. Another method is to isolate
nodes from the network at the network layer once it has been
detected that more traffic is injected into the network than allowed
by a prior set or dynamically adjusted threshold. Finally, if
communication is sufficiently secured, only trusted nodes can
receive and forward traffic which also lowers the risk of an
overload attack.</t>
<t>Receiving nodes that validate signatures and sending nodes that
encrypt messages need to be cautious of cryptographic processing
usage when validating signatures and encrypting messages. Where
feasible, certificates should be validated prior to use of the
associated keys to counter potential resource overloading attacks.
The associated design decision needs to also consider that the
validation process requires resources and thus itself could be
exploited for attacks. Alternatively, resource management limits can
be placed on routing security processing events (see the comment in
Section 6, paragraph 4, of <xref target="RFC5751"/>).</t>
</section>
<section title="Countering Selective Forwarding Attacks">
<t>Selective forwarding attacks are a form of DoS attack which
impacts the availability of the generated routing paths.</t>
<t>A selective forwarding attack may be done by a node involved
with the routing process, or it may be done by what
otherwise appears to be a passive antenna or other RF
feature or device, but is in fact an active (and selective)
device. An RF antenna/repeater which is not selective, is
not a threat.</t>
<t>An insider malicious node basically blends neatly in with the
network but then may decide to forward and/or manipulate certain
packets. If all packets are dropped, then this attacker is also
often referred to as a "black hole". Such a form of attack is
particularly dangerous if coupled with sinkhole attacks since
inherently a large amount of traffic is attracted to the malicious
node and thereby causing significant damage. In a shared medium, an
outside malicious node would selectively jam overheard data flows,
where the thus caused collisions incur selective forwarding.</t>
<t>Selective Forwarding attacks can be countered by deploying a
series of mutually non-exclusive security measures:
<list style="symbols">
<t>multipath routing of the same message over disjoint
paths;</t>
<t>dynamically selecting the next hop from a set of
candidates.</t>
</list>
</t>
<t>The first measure basically guarantees that if a message gets
lost on a particular routing path due to a malicious selective
forwarding attack, there will be another route which successfully
delivers the data. Such a method is inherently suboptimal from an
energy consumption point of view; it is also suboptimal from a
network utilization perspective. The second method basically
involves a constantly changing routing topology in that next-hop
routers are chosen from a dynamic set in the hope that the number of
malicious nodes in this set is negligible. A routing protocol that
allows for disjoint routing paths may also be useful.</t>
</section>
<section title="Countering Sinkhole Attacks">
<t>In sinkhole attacks, the malicious node manages to attract a lot
of traffic mainly by advertising the availability of high-quality
links even though there are none <xref target="Karlof2003"/>. It
hence constitutes a serious attack on availability.</t>
<t>The malicious node creates a sinkhole by attracting a large
amount of, if not all, traffic from surrounding neighbors by
advertising in and outwards links of superior quality. Affected
nodes hence eagerly route their traffic via the malicious node
which, if coupled with other attacks such as selective forwarding,
may lead to serious availability and security breaches. Such an
attack can only be executed by an inside malicious node and is
generally very difficult to detect. An ongoing attack has a profound
impact on the network topology and essentially becomes a problem of
flow control.</t>
<t>Sinkhole attacks can be countered by deploying a series of
mutually non-exclusive security measures:
<list style="symbols">
<t>use geographical insights for flow control;</t>
<t>isolate nodes which receive traffic above a certain
threshold;</t>
<t>dynamically pick up next hop from set of candidates;</t>
<t>allow only trusted data to be received and forwarded.</t>
</list>
</t>
<t>Some LLNs may provide for geolocation services, often derived
from solving triangulation equations from radio delay calculations,
such calculations could in theory be subverted by a sinkhole that
transmitted at precisely the right power in a node to node fashion.
</t>
<t>While geographic knowledge could help assure that traffic always
went in the physical direction desired, it would not assure that
the traffic was taking the most efficient route, as the lowest
cost real route might be match the physical topology; such as when
different parts of an LLN are connected by high-speed wired networks.
</t>
</section>
<section title="Countering Wormhole Attacks">
<t>In wormhole attacks at least two malicious nodes
claim to have a short path between themselves <xref target="Karlof2003"/>.
This changes the availability
of certain routing paths and hence constitutes a serious security
breach.</t>
<t>Essentially, two malicious insider nodes use another, more
powerful, transmitter to communicate with each other and thereby
distort the would-be-agreed routing path. This distortion could
involve shortcutting and hence paralyzing a large part of the
network; it could also involve tunneling the information to another
region of the network where there are, e.g., more malicious nodes
available to aid the intrusion or where messages are replayed, etc.
</t>
<t>
In conjunction with selective forwarding, wormhole attacks can
create race conditions which impact topology maintenance, routing
protocols as well as any security suits built on "time of check" and
"time of use".</t>
<t>A pure Wormhole attack is nearly impossible to detect. A wormhole
which is used in order to subsequently mount another kind of attack
would be defeated by defeating the other attack. A perfect wormhole,
in which there is nothing adverse that occurs to the traffic, would
be difficult to call an attack. The worst thing that a benign wormhole
can do in such a situation is to cease to operate (become unstable),
causing the network to have to recalculate routes.
</t>
<t>A highly unstable wormhole is no different than a radio opaque (i.e. metal)
door that opens and closes a lot. RPL includes
hystersis in its objective functions
<xref target="RFC6719" />
in an attempt to deal with frequent
changes to the ETX between nodes.
</t>
</section>
</section>
</section>
<section anchor="roll-sec-features" title="ROLL Security Features">
<t>The assessments and analysis in <xref target="roll-threats"/>
examined all areas of threats and attacks that could impact routing, and
the countermeasures presented in <xref target="counter-measur"/> were
reached without confining the consideration to means only available to
routing. This section puts the results into perspective and provides a
framework for addressing the derived set of security objectives that
must be met by the routing protocol(s) specified by the ROLL Working
Group. It bears emphasizing that the target here is a generic, universal
form of the protocol(s) specified and the normative keywords are mainly
to convey the relative level of importance or urgency of the features
specified.</t>
<t>In this view, 'MUST' is used to define the requirements that are
specific to the routing protocol and that are essential for an LLN
routing protocol to ensure that routing operation can be maintained.
Adherence to MUST requirements is needed to directly counter attacks
that can affect the routing operation (such as those that can impact
maintained or derived routing/forwarding tables). 'SHOULD' is used to
define requirements that counter indirect routing attacks where such
attacks do not of themselves affect routing but can assist an attacker
in focusing its attack resources to impact network operation (such as
DoS targeting of key forwarding nodes). 'MAY' covers optional
requirements that can further enhance security by increasing the space
over which an attacker must operate or the resources that must be
applied. While in support of routing security, where appropriate, these
requirements may also be addressed beyond the network routing protocol
at other system communications layers.</t>
<t>The first part of this section, <xref target="conff"/> to <xref
target="avaf"/>, is a prescription of ROLL security features of measures
that can be addressed as part of the routing protocol itself. As routing
is one component of an LLN system, the actual strength of the security
services afforded to it should be made to conform to each system's
security policy; how a design may address the needs of the urban,
industrial, home automation, and building automation application domains
also needs to be considered. The second part of this section, <xref
target="keymanage"/> and <xref target="match-needs"/>, discusses system
security aspects that may impact routing but that also require
considerations beyond the routing protocol, as well as potential
approaches.</t>
<t>If an LLN employs multicast and/or anycast, these alternative
communications modes MUST be secured with the same routing security
services specified in this section. Furthermore, irrespective of the
modes of communication, nodes MUST provide adequate physical tamper
resistance commensurate with the particular application domain
environment to ensure the confidentiality, integrity, and availability
of stored routing information.</t>
<section anchor="conff" title="Confidentiality Features">
<t>With regard to confidentiality, protecting the routing/topology
information from unauthorized disclosure is not directly essential to
maintaining the routing function. Breaches of confidentiality may lead
to other attacks or the focusing of an attacker's resources (see <xref
target="confident-threat"/>) but does not of itself directly undermine
the operation of the routing function. However, to protect against,
and reduce consequences from other more direct attacks, routing
information should be protected. Thus, a secured ROLL protocol:
<list style="symbols">
<t>MUST implement payload encryption;</t>
<t>MAY provide tunneling;</t>
<t>MAY provide load balancing.</t>
</list>
</t>
<t>Where confidentiality is incorporated into the routing exchanges,
encryption algorithms and key lengths need to be specified in
accordance with the level of protection dictated by the routing
protocol and the associated application domain transport network. In
terms of the life time of the keys, the opportunity to periodically
change the encryption key increases the offered level of security for
any given implementation. However, where strong cryptography is
employed, physical, procedural, and logical data access protection
considerations may have more significant impact on cryptoperiod
selection than algorithm and key size factors. Nevertheless, in
general, shorter cryptoperiods, during which a single key is applied,
will enhance security.</t>
<t>Given the mandatory protocol requirement to implement routing node
authentication as part of routing integrity (see <xref
target="intf"/>), key exchanges may be coordinated as part of the
integrity verification process. This provides an opportunity to
increase the frequency of key exchange and shorten the cryptoperiod as
a complement to the key length and encryption algorithm required for a
given application domain. For LLNs, the coordination of
confidentiality key management with the implementation of node device
authentication can thus reduce the overhead associated with supporting
data confidentiality. If a new ciphering key is concurrently generated
or updated in conjunction with the mandatory authentication exchange
occurring with each routing peer association, signaling exchange
overhead can be reduced.</t>
</section>
<section anchor="intf" title="Integrity Features">
<t>The integrity of routing information provides the basis for
ensuring that the function of the routing protocol is achieved and
maintained. To protect integrity, RPL must either run using
only the Secure versions of the messages, or must run over
a layer-2 that uses channel binding between node identity
and transmissions. (i.e.: a layer-2 which has an identical
network-wide transmission key can not defend against many attacks)
</t>
<t>XXX. Logging is critical, but presently impossible. </t>
</section>
<section anchor="avaf" title="Availability Features">
<t>Availability of routing information is linked to system and network
availability which in the case of LLNs require a broader security view
beyond the requirements of the routing entities (see <xref
target="match-needs"/>). Where availability of the network is
compromised, routing information availability will be accordingly
affected. However, to specifically assist in protecting routing
availability:
<list style="symbols">
<t>MAY restrict neighborhood cardinality;</t>
<t>MAY use multiple paths;</t>
<t>MAY use multiple destinations;</t>
<t>MAY choose randomly if multiple paths are available;</t>
<t>MAY set quotas to limit transmit or receive volume;</t>
<t>MAY use geographic information for flow control.</t>
</list>
</t>
</section>
<section anchor="keymanage" title="Key Management">
<t>The functioning of the routing security services requires keys and
credentials. Therefore, even though not directly a ROLL security
requirement, an LLN MUST have a process for initial key and credential
configuration, as well as secure storage within the associated devices.
Anti-tampering SHOULD be a consideration in physical design.
Beyond initial credential
configuration, an LLN is also encouraged to have automatic procedures
for the revocation and replacement of the maintained security
credentials.</t>
<t> While RPL has secure modes, but some modes are impractical
without use of public key cryptography believed to be too expensive
by many. RPL layer-3 security will often depend upon existing LLN
layer-2 security mechanisms, which provides for node authentication,
but little in the way of node authorization.
</t>
</section>
<section anchor="match-needs"
title="Consideration on Matching Application Domain Needs">
<t>Providing security within an LLN requires considerations that
extend beyond routing security to the broader LLN application domain
security implementation. In other words, as routing is one component
of an LLN system, the actual strength of the implemented security
algorithms for the routing protocol MUST be made to conform to the
system's target level of security. The development so far takes into
account collectively the impacts of the issues gathered from <xref
target="RFC5548"/>, <xref target="RFC5673"/>, <xref
target="RFC5826"/>, and <xref target="RFC5867"/>. The following two
subsections first consider from an architectural perspective how the
security design of a ROLL protocol may be made to adapt to the four
application domains, and then examine mechanisms and protocol
operations issues.</t>
<section anchor="roll-sec-arch" title="Security Architecture">
<t>The first challenge for a ROLL protocol security design is to
have an architecture that can adequately address a set of very
diverse needs. It is mainly a consequence of the fact that there are
both common and non-overlapping requirements from the four
application domains, while, conceivably, each individual application
will present yet its own unique constraints.</t>
<t>For a ROLL protocol, the security requirements defined in <xref
target="conff"/> to <xref target="keymanage"/> can be addressed at
two levels: 1) through measures implemented directly within the
routing protocol itself and initiated and controlled by the routing
protocol entities; or 2) through measures invoked on behalf of the
routing protocol entities but implemented within the part of the
network over which the protocol exchanges occur.</t>
<t>Where security is directly implemented as part of the routing
protocol the security requirements configured by the user (system
administrator) will operate independently of the lower layers.
OSPFv2 <xref target="RFC2328"/> is an example of such an approach in
which security parameters are exchanged and assessed within the
routing protocol messages. In this case, the mechanism may be, e.g.,
a header containing security material of configurable security
primitives in the fashion of OSPFv2 or RIPv2 <xref
target="RFC2453"/>. Where IPsec <xref target="RFC4301"/> is employed
to secure the network, the included protocol-specific (OSPF or RIP)
security elements are in addition to and independent of those at the
network layer. In the case of LLNs or other networks where system
security mandates protective mechanisms at other lower layers of the
network, security measures implemented as part of the routing
protocol will be redundant to security measures implemented
elsewhere as part of the protocol stack.</t>
<t>Security mechanisms built into the routing protocol can ensure
that all desired countermeasures can be directly addressed by the
protocol all the way to the endpoint of the routing exchange. In
particular, routing protocol Byzantine attacks by a compromised node
that retains valid network security credentials can only be detected
at the level of the information exchanged within the routing
protocol. Such attacks aimed at the manipulation of the routing
information can only be fully addressed through measures operating
directly between the routing entities themselves or external
entities able to access and analyze the routing information (see
discussion in <xref target="counter-byzantine"/>).</t>
<t>On the other hand, it is more desirable from an LLN device
perspective that the ROLL protocol is integrated into the framework
of an overall system architecture where the security facility may be
shared by different applications and/or across layers for
efficiency, and where security policy and configurations can be
consistently specified. See, for example, considerations made in
RIPng <xref target="RFC2080"/> or the approach presented in <xref
target="Messerges2003"/>.</t>
<t>Where the routing protocol is able to rely on security measures
configured within other layers of the protocol stack, greater system
efficiency can be realized by avoiding potentially redundant
security. Relying on an open trust model <xref
target="Messerges2003"/>, the security requirements of the routing
protocol can be more flexibly met at different layers of the
transport network; measures that must be applied to protect the
communications network are concurrently able to provide the needed
routing protocol protection.</t>
<t>For example, where a given security encryption scheme is deemed
the appropriate standard for network confidentiality of data
exchanges at the link layer, that level of security is directly
provided to routing protocol exchanges across the local link.
Similarly, where a given authentication procedure is stipulated as
part of the standard required for authenticating network traffic,
that security provision can then meet the requirement needed for
authentication of routing exchanges. In addition, in the context of
the different LLN application domains, the level of security
specified for routing can and should be consistent with that
considered appropriate for protecting the network within the given
environment.</t>
<t>A ROLL protocol MUST be made flexible by a design that offers the
configuration facility so that the user (network administrator) can
choose the security settings that match the application's needs.
Furthermore, in the case of LLNs, that flexibility SHOULD extend to
allowing the routing protocol security requirements to be met by
measures applied at different protocol layers, provided the
identified requirements are collectively met.</t>
<t>Since Byzantine attackers that can affect the validity of the
information content exchanged between routing entities can only be
directly countered at the routing protocol level, the ROLL protocol
MAY support mechanisms for verifying routing data validity that
extend beyond the chain of trust created through device
authentication. This protocol-specific security mechanism SHOULD be
made optional within the protocol allowing it to be invoked
according to the given routing protocol and application domain and
as selected by the system user. All other ROLL security mechanisms
needed to meet the above identified routing security requirements
can be flexibly implemented within the transport network (at the IP
network layer or higher or lower protocol layers(s)) according to
the particular application domain and user network
configuration.</t>
<t>Based on device capabilities and the spectrum of operating
environments it would be difficult for a single fixed security
design to be applied to address the diversified needs of the urban,
industrial, home, and building ROLL application domains, and
foreseeable others, without forcing a very low common denominator
set of requirements. On the other hand, providing four individual
domain designs that attempt to a priori match each individual domain
is also very unlikely to provide a suitable answer given the degree
of network variability even within a given domain; furthermore, the
type of link layers in use within each domain also influences the
overall security.</t>
<t>Instead, the framework implementation approach recommended is for
optional, routing protocol-specific measures that can be applied
separately from, or together with, flexible transport network
mechanisms. Protocol-specific measures include the specification of
valid parameter ranges, increments and/or event frequencies that can
be verified by individual routing devices. In addition to deliberate
attacks this allows basic protocol sanity checks against
unintentional mis-configuration. Transport network mechanisms would
include out-of-band communications that may be defined to allow an
external entity to request and process individual device information
as a means to effecting an external verification of the derived
network routing information to identify the existence of intentional
or unintentional network anomalies.</t>
<t>This approach allows countermeasures against byzantine attackers
to be applied in environments where applicable threats exist. At the
same time, it allows routing protocol security to be supported
through measures implemented within the transport network that are
consistent with available system resources and commensurate and
consistent with the security level and strength applied in the
particular application domain networks.</t>
</section>
<section anchor="roll-sec-mech" title="Mechanisms and Operations">
<t>With an architecture allowing different configurations to meet
the application domain needs, the task is then to find suitable
mechanisms. For example, one of the main problems of synchronizing
security states of sleepy nodes lies in difficulties in
authentication; these nodes may not have received in time the most
recent update of security material. Similarly, the issues of minimal
manual configuration, prolonged rollout and delayed addition of
nodes, and network topology changes also complicate security
management. In many cases the ROLL protocol may need to bootstrap
the authentication process and allow for a flexible expiration
scheme of authentication credentials. This exemplifies the need for
the coordination and interoperation between the requirements of the
ROLL routing protocol and that of the system security elements.</t>
<t>Similarly, the vulnerability brought forth by some
special-function nodes, e.g., LBRs requires the assurance,
particularly, of the availability of communication channels and node
resources, or that the neighbor discovery process operates without
undermining routing availability.</t>
<t>There are other factors which are not part of a ROLL routing
protocol but which can still affect its operation. These include
elements such as weaker barrier to accessing the data or security
material stored on the nodes through physical means; therefore, the
internal and external interfaces of a node need to be adequate for
guarding the integrity, and possibly the confidentiality, of stored
information, as well as the integrity of routing and route
generation processes.</t>
<t><xref target="Fig5"/> provides an overview of the larger context
of system security and the relationship between ROLL requirements
and measures and those that relate to the LLN system.</t>
<figure align="center" anchor="Fig5"
title="LLN Device Security Model">
<preamble/>
<artwork align="left">
<![CDATA[
Security Services for
ROLL-Addressable
Security Requirements
| |
+---+ +---+
Node_i | | Node_j
_____v___ ___v_____
Specify Security / \ / \ Specify Security
Requirements | Routing | | Routing | Requirements
+---------| Protocol| | Protocol|---------+
| | Entity | | Entity | |
| \_________/ \_________/ |
| | | |
|ROLL-Specified | | ROLL-Specified|
---Interface | | Interface---
| ...................................... |
| : | | : |
| : +-----+----+ +----+-----+ : |
| : |Transport/| |Transport/| : |
____v___ : +>|Network | |Network |<+ : ___v____
/ \ : | +-----+----+ +----+-----+ | : / \
| |-:-+ | | +-:-| |
|Security| : +-----+----+ +----+-----+ : |Security|
+->|Services|-:-->| Link | | Link |<--:-|Services|<-+
| |Entity | : +-----+----+ +----+-----+ : |Entity | |
| | |-:-+ | | +-:-| | |
| \________/ : | +-----+----+ +----+-----+ | : \________/ |
| : +>| Physical | | Physical |<+ : |
Application : +-----+----+ +----+-----+ : Application
Domain User : | | : Domain User
Configuration : |__Comm. Channel_| : Configuration
: :
...Protocol Stack.....................
]]>
</artwork>
<postamble/>
</figure>
</section>
</section>
</section>
<section anchor="IANA" title="IANA Considerations">
<t>This memo includes no request to IANA.</t>
</section>
<section anchor="Security" title="Security Considerations">
<t>The analysis presented in this document provides security analysis
and design guidelines with a scope limited to ROLL. Security services
are identified as requirements for securing ROLL. The specific
mechanisms to be used to deal with each threat is specified in
link-layer and deployment specific applicability statements.</t>
</section>
<!-- Possibly a 'Contributors' section ... -->
<section anchor="Acknowledgements" title="Acknowledgments">
<t>The authors would like to acknowledge the review and comments from
Rene Struik and JP Vasseur. The authors would also like to acknowledge
the guidance and input provided by the ROLL Chairs, David Culler, and JP
Vasseur, and the Area Director Adrian Farrel.</t>
<t>This document started out as a combined threat and solutions
document. As a result of security review, the document was split up by
ROLL co-Chair Michael Richardson and security Area Director Sean Turner
as it went through the IETF publication process. The solutions to the
threads are application and layer-2 specific, and have therefore
been moved to the relevant applicability statements.</t>
<t>Ines Robles kept track of the many issues that were raised during the
development of this document</t>
</section>
</middle>
<!-- *****BACK MATTER ***** -->
<back>
<!-- References split into informative and normative -->
<!-- There are 2 ways to insert reference entries from the citation libraries:
1. define an ENTITY at the top, and use "ampersand character"RFC2629; here (as shown)
2. simply use a PI "less than character"?rfc include="reference.RFC.2119.xml"?> here
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directory as the including file. You can also define the XML_LIBRARY environment variable
with a value containing a set of directories to search. These can be either in the local
filing system or remote ones accessed by http (http://domain/dir/... ).-->
<references title="Normative References">
<!--?rfc include="http://xml.resource.org/public/rfc/bibxml/reference.RFC.2119.xml"?-->
&RFC2119;
&RFC4301;
&RFC4107;
&RFC6550;
&I-D.ietf-roll-terminology;
&RFC6719;
</references>
<references title="Informative References">
<!-- Here we use entities that we defined at the beginning. -->
&I-D.alexander-roll-mikey-lln-key-mgmt;
&RFC1142;
&RFC2080;
&RFC2328;
&RFC2453;
&RFC5055;
&RFC3830;
&RFC4046;
&RFC4732;
&RFC4949;
&RFC4593;
&RFC5197;
&RFC5751;
&RFC5996;
&RFC6192;
<reference anchor="IEEE1149.1">
<front>
<title>IEEE Standard Test Access Port and Boundary Scan
Architecture</title>
<author/>
<date month="Jun. 14" year="2001"/>
</front>
<seriesInfo name="IEEE-SA" value="Standards Board"/>
</reference>
<reference anchor="Kasumi3gpp">
<front>
<title>3GPP TS 35.202 Specification of the 3GPP confidentiality and
integrity algorithms; Document 2: Kasumi specification</title>
<author/>
<date month="" year="2009"/>
</front>
<seriesInfo name="3GPP TSG" value="SA3"/>
</reference>
<reference anchor="FIPS197">
<front>
<title>Federal Information Processing Standards Publication 197:
Advanced Encryption Standard (AES)</title>
<author/>
<date month="Nov. 26" year="2001"/>
</front>
<seriesInfo name="US"
value="National Institute of Standards and Technology"/>
</reference>
<!--
<reference anchor="FIPS180">
<front>
<title>Federal Information Processing Standards Publication 180-3:
Secure Hash Standard (SHS)</title>
<author></author>
<date month="Oct." year="2008" />
</front>
<seriesInfo name="US"
value="National Institute of Standards and Technology" />
</reference>
<reference anchor="SP800-38A">
<front>
<title>NIST Special Publication 800-38A, Recommendation for Block
Cipher Modes of Operation</title>
<author></author>
<date month="Dec." year="2001" />
</front>
<seriesInfo name="US"
value="National Institute of Standards and Technology" />
</reference>
-->
<reference anchor="Perlman1988">
<front>
<title>Network Layer Protocols with Byzantine Robustness</title>
<author initials="N" surname="Perlman">
<organization/>
</author>
<date month="" year="1988"/>
</front>
<seriesInfo name="MIT LCS Tech Report," value="429"/>
</reference>
<reference anchor="Wander2005">
<front>
<title>Energy analysis of public-key cryptography for wireless
sensor networ</title>
<author initials="A.S" surname="Wander">
<organization/>
</author>
<author initials="N" surname="Gura">
<organization/>
</author>
<author initials="H" surname="Eberle">
<organization/>
</author>
<author initials="V" surname="Gupta">
<organization/>
</author>
<author initials="S.C" surname="Shantz">
<organization/>
</author>
<date month="March 8-12" year="2005"/>
</front>
<seriesInfo name="in the Proceedings of the Third IEEE International Conference on Pervasive Computing and Communications"
value="pp. 324-328"/>
</reference>
<reference anchor="Szcze2008" target="http://www.ic.unicamp.br/~leob/publications/ewsn/NanoECC.pdf">
<front>
<title>NanoECC: testing the limits of elliptic curve cryptography in sensor networks</title>
<author initials="P." surname="Szczechowiak1">
<organization/>
</author>
<author initials="L.B." surname="Oliveira">
<organization/>
</author>
<author initials="M." surname="Scott">
<organization/>
</author>
<author initials="M." surname="Collier">
<organization/>
</author>
<author initials="R." surname="Dahab">
<organization/>
</author>
<date year="2008"/>
</front>
<seriesInfo name="" value="pp. 324-328"/>
</reference>
<reference anchor="Karlof2003">
<front>
<title>Secure routing in wireless sensor networks: attacks and
countermeasures</title>
<author initials="C" surname="Karlof">
<organization/>
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<author initials="D" surname="Wagner">
<organization/>
</author>
<date month="September" year="2003"/>
</front>
<seriesInfo name="Elsevier AdHoc Networks Journal, Special Issue on Sensor Network Applications and Protocols,"
value="1(2):293-315"/>
</reference>
&RFC5826;
&RFC5867;
&RFC5548;
&RFC5673;
&I-D.suhopark-hello-wsn;
&I-D.kelsey-intarea-mesh-link-establishment;
&ISO.7498-2.1988;
<!-- &I-D.ietf-rpsec-ospf-vuln; -->
<reference anchor="Myagmar2005">
<front>
<title>Threat Modeling as a Basis for Security Requirements</title>
<author initials="S" surname="Myagmar">
<organization/>
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<author initials="AJ" surname="Lee">
<organization/>
</author>
<author initials="W" surname="Yurcik">
<organization/>
</author>
<date month="Aug 29," year="2005"/>
</front>
<seriesInfo name="in Proceedings of the Symposium on Requirements Engineering for Information Security (SREIS'05),"
value="Paris, France"/>
<seriesInfo name="pp." value="94-102"/>
</reference>
<reference anchor="Huang2003">
<front>
<title>Fast Authenticated Key Establishment Protocols for
Self-Organizing Sensor Networks</title>
<author initials="Q" surname="Huang">
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<author initials="J" surname="Cukier">
<organization/>
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<author initials="H" surname="Kobayashi">
<organization/>
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<author initials="J" surname="Zhang">
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<date month="Sept. 19" year="2003"/>
</front>
<seriesInfo name="in Proceedings of the 2nd ACM International Conference on Wireless Sensor Networks and Applications,"
value="San Diego, CA, USA"/>
<seriesInfo name="pp." value="141-150"/>
</reference>
<reference anchor="Messerges2003">
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<author initials="T" surname="Messerges">
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<organization/>
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<author initials="T" surname="Kevenaar">
<organization/>
</author>
<author initials="L" surname="Puhl">
<organization/>
</author>
<author initials="R" surname="Struik">
<organization/>
</author>
<author initials="E" surname="Callaway">
<organization/>
</author>
<date month="Oct. 31" year="2003"/>
</front>
<seriesInfo name="in Proceedings of the 1st ACM Workshop on Security of Ad Hoc and Sensor Networks,"
value="Fairfax, VA, USA"/>
<seriesInfo name="pp." value="1-11"/>
</reference>
<reference anchor="Wan2004">
<front>
<title>S-RIP: A Secure Distance Vector Routing Protocol</title>
<author initials="T" surname="Wan">
<organization/>
</author>
<author initials="E" surname="Kranakis">
<organization/>
</author>
<author initials="PC" surname="van Oorschot">
<organization/>
</author>
<date month="Jun. 8-11" year="2004"/>
</front>
<seriesInfo name="in Proceedings of the 2nd International Conference on Applied Cryptography and Network Security,"
value="Yellow Mountain, China"/>
<seriesInfo name="pp." value="103-119"/>
</reference>
<reference anchor="Yourdon1979">
<front>
<title>Structured Design</title>
<author initials="E" surname="Yourdon">
<organization/>
</author>
<author initials="L" surname="Constantine">
<organization/>
</author>
<date month="" year="1979"/>
</front>
<seriesInfo name="Yourdon Press," value="New York"/>
<seriesInfo name="Chapter 10, pp." value="187-222"/>
</reference>
</references>
</back>
</rfc>
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| PAFTECH AB 2003-2026 | 2026-04-23 21:45:38 |