A Security Threat Analysis for Routing over Low Power and Lossy Networks
Abstract
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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Considerations on ROLL Security . . . . . . . . . . . . . . . 5
3.1. Routing Assets and Points of Access . . . . . . . . . . . 6
3.2. The CIA Security Reference Model . . . . . . . . . . . . . 9
3.3. Issues Specific to or Amplified in LLNs . . . . . . . . . 10
3.4. ROLL Security Objectives . . . . . . . . . . . . . . . . . 12
4. Threats and Attacks . . . . . . . . . . . . . . . . . . . . . 13
4.1. Threats and Attacks on Confidentiality . . . . . . . . . . 14
4.1.1. Routing Exchange Exposure . . . . . . . . . . . . . . 14
4.1.2. Routing Information (Routes and Network Topology)
Exposure . . . . . . . . . . . . . . . . . . . . . . . 15
4.2. Threats and Attacks on Integrity . . . . . . . . . . . . . 15
4.2.1. Routing Information Manipulation . . . . . . . . . . . 15
4.2.2. Node Identity Misappropriation . . . . . . . . . . . . 16
4.3. Threats and Attacks on Availability . . . . . . . . . . . 16
4.3.1. Routing Exchange Interference or Disruption . . . . . 17
4.3.2. Network Traffic Forwarding Disruption . . . . . . . . 17
4.3.3. Communications Resource Disruption . . . . . . . . . . 18
4.3.4. Node Resource Exhaustion . . . . . . . . . . . . . . . 19
5. Countermeasures . . . . . . . . . . . . . . . . . . . . . . . 19
5.1. Confidentiality Attack Countermeasures . . . . . . . . . . 20
5.1.1. Countering Deliberate Exposure Attacks . . . . . . . . 20
5.1.2. Countering Sniffing Attacks . . . . . . . . . . . . . 20
5.1.3. Countering Traffic Analysis . . . . . . . . . . . . . 21
5.1.4. Countering Physical Device Compromise . . . . . . . . 22
5.1.5. Countering Remote Device Access Attacks . . . . . . . 24
5.2. Integrity Attack Countermeasures . . . . . . . . . . . . . 25
5.2.1. Countering Unauthorized Modification Attacks . . . . . 25
5.2.2. Countering Overclaiming and Misclaiming Attacks . . . 25
5.2.3. Countering Identity (including Sybil) Attacks . . . . 26
5.2.4. Countering Routing Information Replay Attacks . . . . 26
5.2.5. Countering Byzantine Routing Information Attacks . . . 26
5.3. Availability Attack Countermeasures . . . . . . . . . . . 27
5.3.1. Countering HELLO Flood Attacks and ACK Spoofing
Attacks . . . . . . . . . . . . . . . . . . . . . . . 28
5.3.2. Countering Overload Attacks . . . . . . . . . . . . . 29
5.3.3. Countering Selective Forwarding Attacks . . . . . . . 30
5.3.4. Countering Sinkhole Attacks . . . . . . . . . . . . . 31
5.3.5. Countering Wormhole Attacks . . . . . . . . . . . . . 32
6. ROLL Security Features . . . . . . . . . . . . . . . . . . . . 32
6.1. Confidentiality Features . . . . . . . . . . . . . . . . . 33
6.2. Integrity Features . . . . . . . . . . . . . . . . . . . . 34
6.3. Availability Features . . . . . . . . . . . . . . . . . . 35
6.4. Security Key Management . . . . . . . . . . . . . . . . . 36
6.5. Consideration on Matching Application Domain Needs . . . . 37
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6.5.1. Security Architecture . . . . . . . . . . . . . . . . 38
6.5.2. Mechanisms and Operations . . . . . . . . . . . . . . 40
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 42
8. Security Considerations . . . . . . . . . . . . . . . . . . . 42
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 43
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 43
10.1. Normative References . . . . . . . . . . . . . . . . . . . 43
10.2. Informative References . . . . . . . . . . . . . . . . . . 43
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 46
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1. Introduction
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 interface (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.
This document presents a framework for securing Routing Over LLNs
(ROLL) through an analysis that starts from the routing basics. The
objective is two-fold. First, the framework will be used to identify
pertinent security issues. Second, it will facilitate both the
assessment of a protocol's security threats and the identification of
the necessary features for development of secure protocols for the
ROLL Working Group.
The approach adopted in this effort proceeds in four steps, to
examine security issues in ROLL, to analyze threats and attacks, to
consider the countermeasures, and then to make recommendations for
securing ROLL. The basis is found on identifying the assets and
points of access of routing and evaluating their security needs based
on the Confidentiality, Integrity, and Availability (CIA) model in
the context of LLN.
2. Terminology
This document adopts the terminology defined in [RFC6550] and in
[RFC4949], with the following addition:
Node An element of a low power lossy network that may be a router or
a host.
3. Considerations on ROLL Security
Security, in essence, entails implementing measures to ensure
controlled state changes on devices and network elements, both based
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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
proper authorization for actions, authentication, and potentially
confidentiality, 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 assessment can therefore begin with a focus
on the assets or elements of information 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.
This section sets the stage for the development of the framework by
applying the systematic approach proposed in [Myagmar2005] to the
routing security problem, while also drawing references from other
reviews and assessments found in the literature, particularly,
[RFC4593] and [Karlof2003]; thus, the work presented herein may find
use beyond routing for LLNs. 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 CIA 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.
3.1. Routing Assets and Points of Access
An asset implies an important system component (including
information, process, or physical resource), the access to,
corruption or loss of which adversely affects the system. In network
routing, assets lie in the routing information, routing process, and
node's physical resources. That is, the access to, corruption, or
loss of these elements adversely affects system routing. In network
routing, a point of access refers to the point of entry facilitating
communication with or other interaction with a system component in
order to use system resources to either manipulate information or
gain knowledge of the information contained within the system.
Security of the routing protocol must be focused on the assets of the
routing nodes and the points of access of the information exchanges
and information storage that may permit routing compromise. The
identification of routing assets and points of access hence provides
a basis for the identification of associated threats and attacks.
This subsection identifies assets and points of access of a generic
routing process with a level-0 data flow diagram [Yourdon1979]
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revealing how the routing protocol interacts with its environment.
In particular, the use of the data flow diagram allows for a clear,
concise model of the routing functionality; it also has the benefit
of showing the manner in which nodes participate in the routing
process, thus providing context when later threats and attacks are
considered. The goal of the model is to be as detailed as possible
so that corresponding components and mechanisms in an individual
routing protocol can be readily identified, but also to be as general
as possible to maximize the relevancy of this effort for the various
existing and future protocols. Nevertheless, there may be
discrepancies, likely in the form of additional elements, when the
model is applied to some protocols. For such cases, the analysis
approach laid out in this document should still provide a valid and
illustrative path for their security assessment.
Figure 1 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.
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...................................................
: :
: :
|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|
Data flow
Figure 1: Data Flow Diagram of a Generic Routing Process
It is seen from Figure 1 that
o Assets include
* routing and/or topology information;
* communication channel resources (bandwidth);
* node resources (computing capacity, memory, and remaining
energy);
* node identifiers (including node identity and ascribed
attributes such as relative or absolute node location).
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o Points of access include
* neighbor discovery;
* route/topology exchange;
* node physical interfaces (including access to data storage).
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 framework 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.
3.2. The CIA Security Reference Model
At the conceptual level, security within an information system in
general and applied to ROLL in particular is concerned with the
primary issues of confidentiality, integrity, and availability. In
the context of ROLL:
Confidentiality
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.
Integrity
Integrity, as a security principle, entails the protection of
routing information and routing neighbor maintenance exchanges,
as well as derived information maintained in the database, from
unauthorized modification or from misuse. Misuse, for example,
may take the form of a delayed or inappropriately replayed
message even where confidentiality protection is maintained.
Hence, in addition to the data itself, integrity also concerns
the authenticity of claimed identity of the origin and
destination of a message and its timeliness or freshness. On
the other hand, the access to and/or removal of data, execution
of the routing process, and use of a device's computing and
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energy resources, while relevant to routing security are
considered larger system integrity issues [RFC4949] to be
addressed beyond the routing protocol.
Availability
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.
It is recognized that, besides those security issues captured in the
CIA model, non-repudiation, that is, the assurance that the
transmission and/or reception of a message cannot later be denied,
may be a security requirement under certain circumstances. 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 will involve
providing some ability to allow traceability or network management
review of participants of the routing process including the ability
to determine the events and actions leading to a particular routing
state. As such, non-repudiation of routing may thus be more useful
when interworking with networks of different ownerships. For the LLN
application domains as described in [RFC5548], [RFC5673], [RFC5826],
and [RFC5867], particularly with regard to routing security,
proactive measures are much more critical than retrospective
protections. Furthermore, given the significant practical limits to
on-going routing transaction logging and storage and individual
device signature authentication for each exchange, non-repudiation in
the context of routing is not further considered as a ROLL security
issue.
It should be emphasized here that for routing security the above CIA
requirements must be complemented by the proper security policies and
enforcement mechanisms to ensure that security objectives are met by
a given routing protocol implementation.
3.3. Issues Specific to or Amplified in LLNs
The work [RFC5548], [RFC5673], [RFC5826], and [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.
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Limited energy, memory, and processing node resources
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. In addition, the choices of
security mechanisms are more stringent. Synchronization of
security states with sleepy nodes is yet another issue.
Large scale of rolled out network
The possibly numerous nodes to be deployed, e.g., an urban
deployment can see several hundreds of thousands of nodes, as
well as the generally low level of expertise expected of the
installers, make manual on-site configuration unlikely.
Prolonged rollout and delayed addition of nodes, which may be
from old inventory, over the lifetime of the network, also
complicate the operations of key management.
Autonomous operations
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.
Highly directional traffic
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. In fact, when Point-to-MultiPoint
(P2MP) and MultiPoint-to-Point (MP2P) traffic represents a
majority of the traffic, routing attacks consisting of
advertising untruthfully preferred routes may cause serious
damages.
Unattended locations and limited physical security
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.
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Support for mobility
On the one hand, only a 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.
Support for multicast and anycast
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.
The above list considers how a LLN's physical constraints, size,
operations, and varieties 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.
3.4. ROLL Security Objectives
This subsection applies the CIA model to the routing assets and
access points, taking into account the LLN issues, to develop a set
of ROLL security objectives.
Since the fundamental function of a routing protocol is to build
routes for forwarding packets, it is essential to ensure that
o routing/topology information is not tampered during transfer and
in storage;
o routing/topology information is not misappropriated;
o routing/topology information is available when needed.
In conjunction, it is necessary to be assured of
o the authenticity and legitimacy of the participants of the routing
neighbor discovery process;
o the routing/topology information received was faithfully generated
according to the protocol design.
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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 eavesdropping or unauthorized
exposure may be desirable in certain cases but is in itself less
pertinent in general to the routing function.
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.
The vulnerability brought forth by some special-function nodes, e.g.,
LBRs, requires the assurance, particularly in a security context,
o of the availability of communication channels and node resources;
o that the neighbor discovery process operates without undermining
routing availability.
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.
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.
4. Threats and Attacks
This section outlines general categories of threats under the CIA
model and highlights the specific attacks in each of these categories
for ROLL. As defined in [RFC4949], a threat is "a potential for
violation of security, which exists when there is a circumstance,
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capability, action, or event that could breach security and cause
harm." 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."
The subsequent subsections consider the threats and their realizing
attacks that can cause security breaches under the CIA model to the
routing assets and via the routing points of access identified in
Section 3.1. 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 manifestation of the attacks is assumed to be from
either inside or outside attackers, whose capabilities may be limited
to node-equivalent or more sophisticated computing platforms.
4.1. Threats and Attacks on Confidentiality
The assessment in Section 3.2 indicates that routing information
assets are exposed to confidentiality threats from all points of
access. The confidentiality threat space is thus defined by the
access to routing information achievable through the communication
exchanges between routing nodes together with the direct access to
information maintained within the nodes.
4.1.1. Routing Exchange Exposure
Routing exchanges include both routing information as well as
information associated with the establishment and maintenance of
neighbor state information. As indicated in Section 3.1, 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.
The exposure of routing information exchanged will allow unauthorized
sources to gain access to the content of the exchanges between
communicating nodes. The exposure of neighbor state information will
allow unauthorized sources to gain knowledge of communication links
between routing nodes that are necessary to maintain routing
information exchanges.
The forms of attack that allow unauthorized access or exposure of
routing exchange information include
o Deliberate exposure (where one party to the routing exchange is
able to independently provide unauthorized access);
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o Sniffing (passive reading of transmitted data content);
o Traffic analysis (evaluation of the network routing header
information).
4.1.2. Routing Information (Routes and Network Topology) Exposure
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.
The exposure of this information will allow unauthorized sources 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.
The forms of attack that allow unauthorized access or exposure of the
routing information (other than occurring through explicit node
exchanges) will include
o Physical device compromise;
o Remote device access attacks (including those occurring through
remote network management or software/field upgrade interfaces).
More detailed descriptions of the exposure attacks on routing
exchange and information will be given in Section 5 together with the
corresponding countermeasures.
4.2. Threats and Attacks on Integrity
The assessment in Section 3.2 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.
4.2.1. Routing Information Manipulation
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. Manipulation of
topology and reachability information will allow unauthorized sources
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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. For example, being
able to attract network traffic can make a blackhole attack more
damaging.
The forms of attack that allow manipulation to compromise the content
and validity of routing information include
o Falsification, including overclaiming and misclaiming;
o Routing information replay;
o 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, [RFC4593]
for further discussions on Byzantine attacks);
o Physical device compromise or remote device access attacks.
4.2.2. Node Identity Misappropriation
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
o Identity attacks, including Sybil attacks in which a malicious
node illegitimately assumes multiple identities;
o Routing information replay.
4.3. Threats and Attacks on Availability
The assessment in Section 3.2 indicates that the process and
resources assets are exposed to availability threats; attacks of this
category may exploit directly or indirectly information exchange or
forwarding (see [RFC4732] for a general discussion).
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4.3.1. Routing Exchange Interference or Disruption
Interference or disruption of routing information exchanges will
allow unauthorized sources to influence the operation and convergence
of the routing protocols by impeding the regularity of routing
information exchange.
The forms of attack that allow interference or disruption of routing
exchange include
o Routing information replay;
o HELLO flood attacks and ACK spoofing;
o Overload attacks.
In addition, attacks may also be directly conducted at the physical
layer in the form of jamming or interfering.
4.3.2. Network Traffic Forwarding Disruption
The disruption of the network traffic forwarding capability of the
network will undermine the central function of network routers and
the ability to handle user traffic. This threat and the associated
attacks affect the availability of the network because of the
potential to impair the primary capability of the network.
In addition to physical layer obstructions, the forms of attack that
allows disruption of network traffic forwarding include [Karlof2003]
o Selective forwarding attacks;
o Wormhole attacks;
o Sinkhole attacks.
For reference, Figure 2 depicts the above listed three types of
attacks.
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|Node_1|--(msg1|msg2|msg3)-->|Attacker|--(msg1|msg3)-->|Node_2|
(a) Selective Forwarding
|Node_1|-------------Unreachable---------x|Node_2|
| ^
| Private Link |
'-->|Attacker_1|===========>|Attacker_2|--'
(b) Wormhole
|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
Figure 2: Selective Forwarding, Wormhole, and Sinkhole Attacks
4.3.3. Communications Resource Disruption
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
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directly addressed within the underlying subsystem and its
implemented protocol layers.
4.3.4. Node Resource Exhaustion
A potential security threat to routing can arise from attempts to
exhaust the node resource asset by initiating exchanges that can lead
to the undue utilization or 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.
Node resources may also be unduly consumed by the 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
threats 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
o Identity (including Sybil) attacks;
o Routing information replay attacks;
o HELLO flood attacks and ACK spoofing;
o Overload attacks.
5. Countermeasures
By recognizing the characteristics of LLNs that may impact routing
and identifying potential countermeasures, this framework 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 CIA 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.
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5.1. Confidentiality Attack Countermeasures
Attacks on confidentiality 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 sniffing or analysis of
routing traffic, or may attempt access through a component or device
interface of a tampered routing node.
5.1.1. Countering Deliberate Exposure Attacks
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 during the exchange.
A prerequisite to countering this type of confidentiality attacks
associated with the routing/topology exchange 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.
To prevent deliberate exposure, the process that communicating nodes
use for establishing communication session keys must be peer-to-peer,
between the routing initiating and responding nodes, so that neither
node can independently weaken the confidentiality of the exchange
without the knowledge of its communicating peer. A deliberate
exposure attack will therefore require more overt and independent
action on the part of the offending node.
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.
5.1.2. Countering Sniffing Attacks
A sniffing attack seeks to breach routing confidentiality through
passive, direct analysis and processing of the information exchanges
between nodes. A sniffing attack in an LLN that is not based on a
physical device compromise will rely on the attacker attempting to
directly derive information from the over-the-shared-medium routing/
topology communication exchange (neighbor discovery exchanges may of
necessity be conducted in the clear thus limiting the extent to which
the information can be kept confidential).
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Sniffing 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 confidentiality keys and
an agreed confidentiality algorithm. The level of security applied
in providing confidentiality 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 Section 6.5. Because of the
resource constraints of LLN devices, symmetric (private) key session
security 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.
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 [Huang2003]).
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) [FIPS197], adopted by
the U.S. government, or Kasumi-Misty [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 (see
Section 5.1.4 below).
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.
5.1.3. Countering Traffic Analysis
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
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mounted. The traffic analysis attack on a LLN, especially one
founded on shared medium, may be passive and relying on the ability
to read the immutable source/destination routing information that
must remain unencrypted to permit network routing. Alternatively,
attacks can be active through the injection of unauthorized discovery
traffic into the network. By implementing authentication measures
between communicating nodes, active traffic analysis attacks can be
prevented within the LLN thereby reducing confidentiality
vulnerabilities to those associated with passive analysis.
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. Network
analysis through this passive attack will require a wider array of
analysis points and additional processing on the part of the
attacker. Note however that where network traffic is dispersed as a
countermeasure there may be implications beyond routing with regard
to general traffic confidentiality. 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. In LLNs, the diverse radio connectivity and
dynamic links (including potential frequency hopping), or a complex
wiring system hidden from sight, will help to further mitigate
traffic analysis attacks when load balancing is also implemented.
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. With tunneling there is a further requirement that the
encapsulating intermediate nodes apply an additional layer of routing
so that traffic arrives at the destination through dynamic routes.
For some LLNs, memory and processing constraints as well as the
limitations of the communication channel will preclude both the
additional routing traffic overhead and the node implementation
required for tunneling countermeasures to traffic analysis.
5.1.4. Countering Physical Device Compromise
Section 4 identified that many threats to the routing functionality
may involve compromised devices. For the sake of completeness, this
subsection examines how to counter physical device compromise,
without restricting the consideration to only those methods and
apparatuses available to a LLN routing protocol.
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Given the distributed nature of LLNs and the varying environment of
deployed devices, confidentiality of routing assets and points of
access may rely heavily on the security of the routing devices. One
means of precluding attacks on the physical device is to prevent
physical access to the node through other external security means.
However, given the environment in which many LLNs operate, preventing
unauthorized access to the physical device cannot be assured.
Countermeasures must therefore be employed at the device and
component level so that routing/topology or neighbor information and
stored route information cannot be accessed even if physical access
to the node is obtained.
With the physical device in the possession of an attacker,
unauthorized information access can be attempted by probing internal
interfaces or device components. Device security must therefore move
to preventing the reading of device processor code or memory
locations without the appropriate security keys and in preventing the
access to any information exchanges occurring between individual
components. Information access will then be restricted to external
interfaces in which confidentiality, integrity and authentication
measures can be applied.
To prevent component information access, deployed routing devices
must ensure that their implementation avoids address or data buses
being connected to external general purpose input/output (GPIO) pins.
Beyond this measure, an important component interface to be protected
against attack is the Joint Test Action Group (JTAG) [IEEE1149.1]
interface used for component and populated circuit board testing
after manufacture. To provide security on the routing devices,
components should be employed that allow fuses on the JTAG interfaces
to be blown to disable access. This will raise the bar on
unauthorized component information access within a captured device.
At the device level a key component information exchange is between
the microprocessor and its associated external memory. While
encryption can be implemented to secure data bus exchanges, the use
of integrated physical packaging which avoids inter-component
exchanges (other than secure external device exchanges) will increase
routing security against a physical device interface attack. With an
integrated package and disabled internal component interfaces, the
level of physical device security can be controlled by managing the
degree to which the device packaging is protected against expert
physical decomposition and analysis.
The device package should be hardened such that attempts to remove
the integrated components will result in damage to access interfaces,
ports or pins that prevent retrieval of code or stored information.
The degree of Very Large Scale Integration (VLSI) or Printed Circuit
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Board (PCB) package security through manufacture can be selected as a
trade-off or desired security consistent with the level of security
achieved by measures applied for other routing assets and points of
access. With package hardening and restricted component access
countermeasures, the security level will be raised to that provided
by measures employed at the external communications interfaces.
Another area of node interface vulnerability is that associated with
interfaces provided for remote software or firmware upgrades. This
may impact both routing information and routing/topology exchange
security where it leads to unauthorized upgrade or change to the
routing protocol running on a given node as this type of attack can
allow for the execution of compromised or intentionally malicious
routing code on multiple nodes. Countermeasures to this device
interface confidentiality attack needs to be addressed in the larger
context of node remote access security. This will ensure not only
the authenticity of the provided code (including routing protocol)
but that the process is initiated by an authorized (authenticated)
entity. For example, digital signing of firmware by an authorized
entity will provide an appropriate countermeasure.
The above identified countermeasures against attacks on routing
information confidentiality through internal device interface
compromise must be part of the larger LLN system security as they
cannot be addressed within the routing protocol itself. Similarly,
the use of field tools or other devices that allow explicit access to
node information must implement security mechanisms to ensure that
routing information can be protected against unauthorized access.
These protections will also be external to the routing protocol and
hence not part of ROLL.
5.1.5. Countering Remote Device Access Attacks
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.
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.
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5.2. Integrity Attack Countermeasures
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.
5.2.1. Countering Unauthorized Modification Attacks
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.
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.
The countermeasure to unauthorized modifications needs to
o implement access control on storage;
o provide data integrity service to transferred messages and stored
data;
o include sequence number under integrity protection.
5.2.2. Countering Overclaiming and Misclaiming Attacks
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.
The counter to overclaiming and misclaiming may employ
o comparison with historical routing/topology data;
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o designs which restrict realizable network topologies.
5.2.3. Countering Identity (including Sybil) Attacks
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.
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
explicit or implicit an asset to an application running on the LLN,
for exa