Networking Working Group T. Tsao, Ed.
Internet-Draft R. Alexander, Ed.
Intended status: Informational Eka Systems
Expires: October 1, 2010 M. Dohler, Ed.
CTTC
V. Daza, Ed.
A. Lozano, Ed.
Universitat Pompeu Fabra
March 30, 2010
A Security Framework for Routing over Low Power and Lossy Networks
draft-ietf-roll-security-framework-00
Abstract
This document presents a security framework for routing over low
power and lossy networks. 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 and
identifying applicable countermeasures. These assessments provide
the basis of the security recommendations for incorporation into low
power, lossy network routing protocols. As an illustration, this
framework is applied to RPL.
Requirements Language
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 RFC
2119 [RFC2119].
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
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Table of Contents
1. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. Considerations on ROLL Security . . . . . . . . . . . . . . . 5
3.1. Routing Assets and Points of Access . . . . . . . . . . . 6
3.2. The CIA Security Reference Model . . . . . . . . . . . . . 8
3.3. Issues Specific to or Amplified in LLNs . . . . . . . . . 9
3.4. ROLL Security Objectives . . . . . . . . . . . . . . . . . 11
4. Threats and Attacks . . . . . . . . . . . . . . . . . . . . . 12
4.1. Threats and Attacks on Confidentiality . . . . . . . . . . 12
4.1.1. Routing Exchange Exposure . . . . . . . . . . . . . . 12
4.1.2. Routing Information (Routes and Network Topology)
Exposure . . . . . . . . . . . . . . . . . . . . . . . 13
4.2. Threats and Attacks on Integrity . . . . . . . . . . . . . 13
4.2.1. Routing Information Manipulation . . . . . . . . . . . 14
4.2.2. Node Identity Misappropriation . . . . . . . . . . . . 14
4.3. Threats and Attacks on Availability . . . . . . . . . . . 15
4.3.1. Routing Exchange Interference or Disruption . . . . . 15
4.3.2. Network Traffic Forwarding Disruption . . . . . . . . 15
4.3.3. Communications Resource Disruption . . . . . . . . . . 15
4.3.4. Node Resource Exhaustion . . . . . . . . . . . . . . . 16
5. Countermeasures . . . . . . . . . . . . . . . . . . . . . . . 16
5.1. Confidentiality Attack Countermeasures . . . . . . . . . . 17
5.1.1. Countering Deliberate Exposure Attacks . . . . . . . . 17
5.1.2. Countering Sniffing Attacks . . . . . . . . . . . . . 17
5.1.3. Countering Traffic Analysis . . . . . . . . . . . . . 19
5.1.4. Countering Physical Device Compromise . . . . . . . . 19
5.1.5. Countering Remote Device Access Attacks . . . . . . . 21
5.2. Integrity Attack Countermeasures . . . . . . . . . . . . . 21
5.2.1. Countering Tampering Attacks . . . . . . . . . . . . . 22
5.2.2. Countering Overclaiming and Misclaiming Attacks . . . 22
5.2.3. Countering Identity (including Sybil) Attacks . . . . 22
5.2.4. Countering Routing Information Replay Attacks . . . . 23
5.2.5. Countering Byzantine Routing Information Attacks . . . 23
5.3. Availability Attack Countermeasures . . . . . . . . . . . 24
5.3.1. Countering HELLO Flood Attacks and ACK Spoofing
Attacks . . . . . . . . . . . . . . . . . . . . . . . 24
5.3.2. Countering Overload Attacks . . . . . . . . . . . . . 26
5.3.3. Countering Selective Forwarding Attacks . . . . . . . 27
5.3.4. Countering Sinkhole Attacks . . . . . . . . . . . . . 27
5.3.5. Countering Wormhole Attacks . . . . . . . . . . . . . 28
6. ROLL Security Features . . . . . . . . . . . . . . . . . . . . 28
6.1. Confidentiality Features . . . . . . . . . . . . . . . . . 29
6.2. Integrity Features . . . . . . . . . . . . . . . . . . . . 30
6.3. Availability Features . . . . . . . . . . . . . . . . . . 31
6.4. Additional Related Features . . . . . . . . . . . . . . . 31
6.5. Consideration on Matching Application Domain Needs . . . . 31
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6.5.1. Security Architecture . . . . . . . . . . . . . . . . 32
6.5.2. Mechanisms and Operations . . . . . . . . . . . . . . 34
7. Application of ROLL Security Framework to RPL . . . . . . . . 36
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38
9. Security Considerations . . . . . . . . . . . . . . . . . . . 38
10. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 38
11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 38
11.1. Normative References . . . . . . . . . . . . . . . . . . . 38
11.2. Informative References . . . . . . . . . . . . . . . . . . 39
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 40
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1. Terminology
This document conforms to the terminology defined in
[I-D.ietf-roll-terminology].
2. Introduction
In recent times, networked wireless devices have found an increasing
number of applications in various fields. Yet, for reasons ranging
from operational application to economics, these wireless devices are
often supplied with minimum physical resources, e.g., limited power
reserve, slow speed or low capability computation, or small memory
size. 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.
This document presents a framework for securing routing over low
power and lossy networks (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 ROLL.
The approach adopted in this effort proceeds in four steps, to
examine ROLL security issues, 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. The utility of this framework is demonstrated
with an application to RPL [I-D.ietf-roll-rpl].
3. Considerations on ROLL Security
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]. 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 of 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
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security objectives for ROLL.
3.1. Routing Assets and Points of Access
An asset implies 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. 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 determine their neighbors (neighbor discovery).
Using the neighboring relationships, routing protocols may exchange
network topology (including link-specific information) to generate
routes or may exchange routes directly as part of a routing exchange;
nodes which do not directly participate in the process with a given
node will get the route/topology information relayed from others. It
is likely that a node will store some or all of the routes and
topology information according to tradeoffs of node resources and
latency associated with the particular routing protocol. The nodes
use the derived routes for making forwarding decisions.
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...................................................
: :
: _________________ :
|Node_i|<------->(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
________
DataBase A data storage DataBase
--------
|Node_n| An external entity Node_n
-------> 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. Indeed, the intention
is to be comprehensive; nonetheless, the discussions to follow on
physical related issues are not related to routing protocol design
but 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 of the wireless, and sometimes ad hoc, nature of the
network, 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
misuse or unauthorized and improper modification. In addition,
integrity also requires the authenticity of claimed identity in
the origin and destination of a message, access and removal of
data, execution of the routing process, and use of computing
and energy resources.
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)
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and forwarding services so as not to impair or limit the
network's central traffic flow function.
It is noted that, besides those captured in the CIA model, non-
repudiation is a security interest under certain circumstances. With
respect 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. Non-repudiation implies after the fact and thus relies on the
logging or other capture of on-going routing exchanges. Given the
limited resources of a node and potentially the communication
channel, and considering the operating mode associated with LLNs,
routing transaction logging or auditing process communication
overhead will not be practical; as such, non-repudiation is not
further considered as a relevant ROLL security issue.
3.3. Issues Specific to or Amplified in LLNs
The work [RFC5548] and [RFC5673], as well as two other ongoing
efforts, [I-D.ietf-roll-home-routing-reqs] and
[I-D.ietf-roll-building-routing-reqs], have identified ROLL specific
requirements and constraints 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.
Limited energy reserve, memory, and processing resources
As a consequence of these constraints, there is an even more
critical need than usual for a careful trade study 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 issues.
Large scale of rolled out network
The possibly numerous nodes to be deployed, as well as the
general level of expertise 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 ROLL. In other words, a ROLL protocol needs to
contain elements of ad hoc networking and cannot rely on manual
configuration for initialization or local filtering rules.
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Network topology/ownership changes, partitioning or merging, as
well as node replacement, can all contribute to key management
issues.
Highly directional traffic
Some types of LLNs see a high percentage of their total traffic
traverse between the nodes and the gateways where the LLNs
connect to wired networks. The special routing status of and
the greater volume of traffic near the gateways/sinks have
routing security consequences.
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.
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. As these are relatively new routing
technologies, there has been an ongoing effort devoted to their
security mechanisms, e.g., from the IETF Multicast Security
working group. However, inclusion of such mechanisms in a
routing protocol, and consequently their security analysis, are
still areas not fully developed or their impact entirely
understood, whether in a more traditional wired or wireless
network, or LLN.
The above list considers how a LLN's physical constraints, size,
operations, and varieties of application areas may impact security.
It is noted here also that LLNs commonly have the majority, if not
all, of their nodes equipped to route. One of the consequences is
that the distinction between the link and network layers become
artificial in some respects. Similarly, the distinction between a
host and a router is blurred, especially when the set of applications
running on a node is small. The continued evolution of ROLL and its
security functionality requirements need close attention.
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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 fundament 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
neighbor discovery process;
o the routing/topology information received was faithfully generated
according to the protocol design.
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 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, ROLL 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.,
gateways/sinks requires the assurance, particularly,
o of the availability of communication channels and node resources;
o that the neighbor discovery process operates without undermining
routing availability.
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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 give a closer look at how the
ROLL security objectives may be compromised and countered,
respectively.
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,
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
assets identified in Section 3.1. The analysis steps through the
security concerns of each routing asset and looks at the attacks that
can exploit points of access. 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 information assets are
exposed to confidentiality threats from all points of access.
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.
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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, as reported in the literature, include
o Deliberate exposure;
o Sniffing;
o Traffic analysis.
4.1.2. Routing Information (Routes and Network Topology) Exposure
Routes 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.
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4.2.1. Routing Information Manipulation
Manipulation of routing information 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 neighbor state (topology) 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.
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;
o Physical device compromise.
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 (including Sybil) attacks;
o Routing information replay.
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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.
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.
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.
The forms of attack that allows disruption of network traffic
forwarding include
o Selective forwarding attacks;
o Sinkhole attacks;
o Wormhole 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
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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.
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 of 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.
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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.
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 symmetric at
each node 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
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physical device compromise will rely on the attacker attempting to
directly derive information from the over-the-air 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).
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. Because of
the resource constraints of LLN devices, symmetric (private) key
session security will provide the best tradeoff 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 AES (adopted by the U.S. government) or Kasumi-Misty (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
tradeoff 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.
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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
mounted. The traffic analysis attack on a LLN 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. In LLNs, the diverse radio connectivity and dynamic links
(including potential frequency hopping) will help to further mitigate
traffic analysis attacks when load balancing is 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 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
Given the distributed nature of LLNs, confidentiality of routing
assets and points of access will 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
LLNs operate, preventing unauthorized access to the physical device
cannot be assured. Countermeasures must therefore be employed at the
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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) 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 it 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 VLSI or PCB package security through manufacture can be
selected as a tradeoff 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
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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.
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 device local or remote 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.
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 tampering
actions and the overclaiming and misclaiming content. The countering
of physical compromise was considered in the previous section and is
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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 Tampering Attacks
Tampering 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.
Tampering 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 tampering 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 is not necessarily tampering. 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;
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
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extension to new areas, e.g., where geographic distribution is
explicit or implicit an asset to an application running on the LLN.
The counter of identity attacks need to ensure the authenticity and
liveliness of the parties of a message exchange; the measure may use
shared key or public key based authentication scheme. On the one
hand, the large-scale nature of the LLNs makes the network-wide
shared key scheme undesirable from a security perspective; on the
other hand, public-key based approaches generally require more
computational resources. Each system will need to make trade-off
decisions based on its security requirements.
5.2.4. Countering Routing Information Replay Attacks
In routing, message replay can result in false topology and/or
routes. The counter of replay attacks need to ensure the freshness
of the message. On the one hand, there are a number of mechanisms
commonly used for countering replay. On the other hand, the choice
should take into account how a particular mechanism is made available
in a LLN. For example, many LLNs have a central source of time and
have it distributed by relaying, such that secured time distribution
becomes a prerequisite of using timestamping to counter replay.
5.2.5. Countering Byzantine Routing Information Attacks
Where a node is captured or compromized 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.
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 principals can therefore only provide a limited
counter against internal (Byzantine) node attacks.
For link state routing protocols where information is flooded
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.
For distance vector protocols where information is aggregated at each
routing node it is not possible for nodes to directly detect
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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 [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.
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
framework, any protection against Byzantine routing information
attacks will need to be directly included within the mechanisms of
the ROLL routing protocol. This can be implemented where such an
attack is considered relevant even within the physical device
protections discussed in Section 5.1.4
5.3. Availability Attack Countermeasures
As alluded to before, availability requires that routing information
exchanges and forwarding mechanisms be available when needed so as to
guarantee a 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 Section 5.2.3 and
Section 5.2.4, respectively.
5.3.1. Countering HELLO Flood Attacks and ACK Spoofing Attacks
HELLO Flood [Karlof2003],[I-D.suhopark-hello-wsn] and ACK Spoofing
attacks are different but highly related forms of attacking a LLN.
They essentially lead nodes to believe that suitable routes are
available even though they are not and hence constitute a serious
availability attack.
The origin of facilitating a HELLO flood attack lies in the fact that
many wireless routing protocols require nodes to send HELLO packets
either upon joining or in regular intervals so as to announce or
confirm their existence to the network. Those nodes that receive the
HELLO packet assume that they are within radio range of the
transmitter by means of a bidirectional communication link.
With this in mind, a malicious node can send or replay HELLO packets
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using a higher transmission power. That creates the false illusion
of being a neighbor to an increased number of nodes in the network,
thereby effectively increasing its unidirectional neighborhood
cardinality. The high quality of the falsely advertised link may
coerce nodes to route data via the malicious node. However, those
affected nodes, for which the malicious node is out of radio range,
never succeed in their delivery and the packets are effectively
dropped. The symptoms are hence similar to those of a sinkhole,
wormhole and selective forwarding attack.
A malicious HELLO flood attack clearly distorts the network topology.
It thus affects protocols building and maintaining the network
topology as well as routing protocols as such, since the attack is
primarily targeted on protocols that require sharing of information
for topology maintenance or flow control.
To counter HELLO flood attacks, several mutually non-exclusive
methods are feasible:
o restricting neighborhood cardinality;
o facilitating multipath routing;
o verifying bidirectionality.
Restricting the neighborhood cardinality prevents malicious nodes
from having an extended set of neighbors beyond some tolerated
threshold and thereby preventing topologies to be built where
malicious nodes have an extended neighborhood set. Furthermore, as
shown in [I-D.suhopark-hello-wsn], if the routing protocol supports
multiple paths from a sensing node towards several gateways then
HELLO flood attacks can also be diminished; however, the energy-
efficiency of such approach is clearly sub-optimal. Finally,
verifying that the link is truly bidirectional by means of, e.g., an
ACK handshake and appropriate security measures ensures that a
communication link is only established if not only the affected node
is within range of the malicious node but also vice versa. Whilst
this does not really eliminate the problem of HELLO flooding, it
greatly reduces the number of affected nodes and the probability of
such an attack succeeding.
As for the latter, the adversary may spoof the ACK messages to
convince the affected node that the link is truly bidirectional and
thereupon drop, tunnel or selectively forward messages. Such ACK
spoofing attack is possible if the malicious node has a receiver
which is significantly more sensitive than that of a normal node,
thereby effectively extending its range. Since an ACK spoofing
attack facilitates a HELLO flood attack, similar countermeasure are
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applicable here. Viable counter and security measures for both
attacks have been exposed in [I-D.suhopark-hello-wsn].
5.3.2. Countering Overload Attacks
Overload attacks are a form of DoS attack in that a malicious node
overloads the network with irrelevant traffic, thereby draining the
nodes' energy budget quicker. It thus significantly shortens the
network lifetime and hence constitutes another serious availability
attack.
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 a LLN node is to have the malicious node
overload the network with irrelevant traffic. This impacts
availability since certain routes get congested which
o renders them useless for affected nodes and data can hence not be
delivered;
o makes routes longer as shortest path algorithms work with the
congested network;
o depletes nodes quicker and thus shortens the network's
availability at large.
Overload attacks can be countered by deploying a series of mutually
non-exclusive security measures:
o introduce quotas on the traffic rate each node is allowed to send;
o isolate nodes which send traffic above a certain threshold;
o allow only trusted data to be received and forwarded.
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 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.
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5.3.3. Countering Selective Forwarding Attacks
Selective forwarding attacks are another form of DoS attack which
impacts the routing path availability.
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. An outside malicious node would selectively jam
overheard data flows, where the thus caused collisions incur
selective forwarding.
Selective Forwarding attacks can be countered by deploying a series
of mutually non-exclusive security measures:
o multipath routing of the same message over disjoint paths;
o dynamically select the next hop from a set of candidates.
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 method is inherently suboptimal from an energy
consumption point of view. 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.
5.3.4. Countering Sinkhole Attacks
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. It hence constitutes a serious attack on
availability.
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.
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Sinkhole attacks can be countered by deploying a series of mutually
non-exclusive security measures:
o use geographical insights for flow control;
o isolate nodes which receive traffic above a certain threshold;
o dynamically pick up next hop from set of candidates;
o allow only trusted data to be received and forwarded.
Whilst most of these countermeasures have been discussed before, the
use of geographical information deserves further attention.
Essentially, if geographic positions of nodes are available, then the
network can assure that data is actually routed towards the sink(s)
and not elsewhere. On the other hand, geographic position is a
sensitive information that may have security and/or privacy
consequences.
5.3.5. Countering Wormhole Attacks
In wormhole attacks at least two malicious nodes shortcut or divert
the usual routing path by means of a low-latency out-of-band channel.
This changes the availability of certain routing paths and hence
constitutes a serious security breach.
Essentially, two malicious insider nodes use another, more powerful,
radio 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. 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".
Wormhole attacks are very difficult to detect in general but can be
mitigated using similar strategies as already outlined above in the
context of sinkhole attacks.
6. ROLL Security Features
The assessments and analysis in Section 4 examined all areas of
threats and attacks that could impact routing, and the
countermeasures presented in Section 5 were reached without confining
the consideration to means only available to routing. This section
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puts the results into perspective and provides a framework for
addressing the derived set of security objectives that must be met by
the ROLL protocol. It bears emphasizing that the target here is a
generic ROLL protocol and the normative keywords are mainly to convey
the relative level of urgency of the features specified.
The first part of this section, Section 6.1 to Section 6.3, 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 a 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, Section 6.4 and Section 6.5, discusses system security
aspects that may impact routing but that also require considerations
beyond the routing protocol, as well as potential approaches.
6.1. Confidentiality Features
With regard to confidentiality, protecting the routing/topology
information from eavesdropping or unauthorized exposure 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 Section 4.1) but does not of itself
directly undermine the operation of the routing function. However,
to protect against, and improve vulnerability against other more
direct attacks, routing information confidentiality should be
protected. Thus, a secured ROLL protocol
o SHOULD provide payload encryption;
o MAY provide tunneling;
o MAY provide load balancing;
o SHOULD provide privacy, e.g., when geographic information is used.
Where confidentiality is incorporated into the routing exchanges,
encryption algorithms and key lengths need to be specified in
accordance of 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
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general, shorter cryptoperiods, during which a single key is applied,
will enhance security.
Given the mandatory protocol requirement to implement routing node
authentication as part of routing integrity (see Section 6.2), 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 compliment 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. A new
ciphering key may therefore be concurrently generated or updated in
conjunction with the mandatory authentication exchange occurring with
each routing peer association.
6.2. Integrity Features
The integrity of routing information provides the basis for ensuring
that the function of the routing protocol is achieved and maintained.
To protect integrity, a secured ROLL protocol
o MUST verify message integrity;
o MUST verify the authenticity and liveliness of both principals of
a connection;
o MUST verify message sequence.
Depending on the nature of the routing protocol, e.g., distance
vector or link state, additional measures may be necessary when the
validity of the routing information is of concern. Specifically,
verification of routing peer authenticity and liveliness can be used
to build a "chain of trust" along the path the routing information
flows, such that network-wide information is validated through the
concatenation of trust established at each individual routing peer
exchange. This is particularly important in the case of distance
vector-based routing protocols, where information is updated at
intermediate nodes, In such cases, there are no direct means within
routing for a receiver to verify the validity of the routing
information beyond the current exchange; as such, nodes would need to
be able to communicate and request information from non-adjacent
peers (see [Wan2004]) to provide information integrity assurances.
With link state-based protocols, on the other hand, routing
information can be signed at the source thus providing a means for
validating information that originates beyond a routing peer.
Therefore, where necessary, a secured ROLL protocol
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o MAY use security auditing mechanisms that are external to routing
to verify the validity of the routing information content
exchanged among routing peers.
6.3. Availability Features
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
Section 6.5). Where availability of the network is compromised,
routing information availability will be accordingly affected.
However, to specifically assist in protecting routing availability
o MAY restrict neighborhood cardinality;
o MAY use multiple paths;
o MAY use multiple destinations;
o MAY choose randomly if multiple paths are available;
o MAY set quotas to limit transmit or receive volume;
o MAY use geographic insights for flow control.
6.4. Additional Related Features
If a LLN employs multicast and/or anycast, it MUST secure these
protocols with the services listed in this sections. Furthermore,
the nodes MUST provide adequate physical tamper resistance to ensure
the integrity of stored routing information.
The functioning of the security services requires keys and
credentials. Therefore, even though not directly a ROLL security
requirement, a LLN must include a process for key and credential
distribution; a LLN is encouraged to have procedures for their
revocation and replacement.
6.5. Consideration on Matching Application Domain Needs
As routing is one component of a 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 is considered as part of the security
architecture in Section 6.5.1.
The development so far takes into account collectively the impacts of
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the issues gathered from [RFC5548], [RFC5673],
[I-D.ietf-roll-home-routing-reqs], and
[I-D.ietf-roll-building-routing-reqs]. 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 mechanism and protocol
operations issues.
6.5.1. Security Architecture
The first challenge for a ROLL protocol security design is to have an
architecture that can adequately address a set of very diversified
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.
For a ROLL protocol, the security requirements defined in Section 6.1
to Section 6.4 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 transport network over which the protocol
exchanges occur.
Where security is directly implemented as part of the routing
protocol the security requirements configured by the user (system
administrator) will operate independent of the underlying transport
network. OSPFv2 [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 [RFC2453]. Where IPsec
[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 transport network, security measures
implemented as part of the routing protocol will be redundant to
security measures implemented elsewhere as part of the transport
network.
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
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attacks aimed 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 Section 5.2.5).
On the other hand, it is more desirable from a 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 [RFC2080] or the
approach presented in [Messerges2003].
Where the routing protocol is able to rely on security measures
configured with the transport network, greater system efficiency can
be realized by avoiding potentially redundant security. Relying on
an open trust model [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.
In addition, in the context of the different application domains, it
allows the level of security applied for routing to be consistent
with that needed for protecting the network itself. For example,
where AES-128 is deemed the appropriate standard for network
confidentiality of data exchanges at the link layer, that level of
security is automatically afforded to routing protocol exchanges.
Similarly, where SHA-1 is stipulated as the standard required for
authenticating routing protocol peers, the use of SHA-1 at the
network layer between communicating routing devices automatically
meets the routing protocol security requirement within the context of
open trust across layers within the device.
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.
Since Byzantine attacks 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
extends beyond the chain of trust created through device
authentication. This protocol-specific security mechanism should be
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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 should 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.
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 four ROLL
application domains 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 likely to provide a suitable answer given the degree of network
variability even within a given domain. Instead, the framework
implementation approach recommended for optional, routing protocol-
specific measures together with flexible transport network mechanisms
can be the most effective. This approach allows countermeasures
against internal attacks to be applied in environments where
applicable threats exist. At the same time, it allows routing
protocol security to be configured through measures implemented
within the transport network that is commensurate and consistent with
the level and strength applied in the particular application domain
networks.
6.5.2. Mechanisms and Operations
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, 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 security management. In such case the ROLL protocol
may need to bootstrap the authentication process and allow for
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.
Similarly, the vulnerability brought forth by some special-function
nodes, e.g., gateways/sinks requires the assurance, particularly, of
the availability of communication channels and node resources, or
that the neighbor discovery process operates without undermining
routing availability.
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There and other factors which are not part of a ROLL routing protocol
can still affect its operation. This includes 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.
Figure 2 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.
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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
: :
...Transport Network..................
Figure 2: LLN Device Security Model
7. Application of ROLL Security Framework to RPL
This section applies the assessments given in Section 6 to RPL as an
illustration of the application of the LLN security framework.
Specializing the approach used in Section 3.1, Figure 3 gives a
level-1 data flow diagram representation of RPL to show the routing
"assets" and "points of access" that may be vulnerable and need to be
protected.
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............................................
: :
|Link-Local : :
Multicast : :
or Node_i|<----->(DIO/DIS/DAO)<--------------+ :
: ^ | :
: | ______V______ :
: | Candidate :
: V Neighbor List :
: (RPL Control incl. ------+------ :
: Trickle Timer, | :
: Loop Avoidance) V :
: ^ (Route Generation) :
: | | :
: | ______V______ :
: +------+ Routing Table :
: | ------+------ :
: | | :
: RPL on Node_j | | :
..................|.............|...........
| |
|Forwarding V |
To/From Node_k|<-------->(Read/Write |
Flow Label)<-------+
Figure 3: Data Flow Diagram of RPL
From Figure 3, it is seen that threats to the proper operation of RPL
are realized through attacks on its DIO, DIS, and DAO messages, as
well as on the information the protocol places on the IPv6 Flow
Labels. As set forth in Section 6.1 to Section 6.4, the base
security requirements concern message integrity, authenticity and
liveliness of the principals of a connection, and protection against
message replay; message encryption may be desirable. The security
objectives for RPL are therefore to ensure that
1. participants of the DIO, DIS, and DAO message exchanges are
authentic;
2. the received DIO, DIS, and DAO messages are not modified during
transportation;
3. the received DIO, DIS, and DAO messages are not retransmissions
of previous messages;
4. the content of the DIO, DIS, and DAO messages may be made legible
to only authorized entities.
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In meeting the above objectives, RPL also needs to provide tunable
mechanisms both to allow matching the security afforded to the
application domain requirements and to enable efficient use of system
resources, as discussed in Section 6.5.1 and Section 6.5.2.
The functions of the different RPL messages and information placed
within the user data plane Flow Labels are factors that can be taken
into account when deciding the optional security features and levels
of strength to be afforded. For example, the DIO messages build
routes to roots while the DAO messages support the building of
downward routes to leaf nodes. Consequently, there may be
application environments in which the directions of the routes have
different importance and thus warrant the use of different security
features and/or strength. In other words, it may be desirable to
have an RPL security design that extends the tunability of the
security features and strengths to message types. The use of a per-
message security specification will allow flexibility in permitting
application-domain security choices as well as overall tunability.
8. IANA Considerations
This memo includes no request to IANA.
9. Security Considerations
The framework 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
results are applied to RPL, with consequent recommendations.
10. Acknowledgments
The authors would like to acknowledge the review and comments from
Rene Struik.
11. References
11.1. Normative References
[RFC2080] Malkin, G. and R. Minnear, "RIPng for IPv6", RFC 2080,
January 1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC2453] Malkin, G., "RIP Version 2", STD 56, RFC 2453,
November 1998.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
11.2. Informative References
[Huang2003]
Huang, Q., Cukier, J., Kobayashi, H., Liu, B., and J.
Zhang, "Fast Authenticated Key Establishment Protocols for
Self-Organizing Sensor Networks", in Proceedings of the
2nd ACM International Conference on Wireless Sensor
Networks and Applications, San Diego, CA, USA, pp. 141-
150, Sept. 19 2003.
[I-D.ietf-roll-building-routing-reqs]
Martocci, J., Riou, N., Mil, P., and W. Vermeylen,
"Building Automation Routing Requirements in Low Power and
Lossy Networks", draft-ietf-roll-building-routing-reqs-09
(work in progress), January 2010.
[I-D.ietf-roll-home-routing-reqs]
Brandt, A. and J. Buron, "Home Automation Routing
Requirements in Low Power and Lossy Networks",
draft-ietf-roll-home-routing-reqs-11 (work in progress),
January 2010.
[I-D.ietf-roll-rpl]
Winter, T., Thubert, P., and R. Team, "RPL: IPv6 Routing
Protocol for Low power and Lossy Networks",
draft-ietf-roll-rpl-07 (work in progress), March 2010.
[I-D.ietf-roll-terminology]
Vasseur, J., "Terminology in Low power And Lossy
Networks", draft-ietf-roll-terminology-03 (work in
progress), March 2010.
[I-D.suhopark-hello-wsn]
Park, S., "Routing Security in Sensor Network: HELLO Flood
Attack and Defense", draft-suhopark-hello-wsn-00 (work in
progress), December 2005.
[Karlof2003]
Karlof, C. and D. Wagner, "Secure routing in wireless
sensor networks: attacks and countermeasures", Elsevier
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AdHoc Networks Journal, Special Issue on Sensor Network
Applications and Protocols, 1(2):293-315, September 2003.
[Messerges2003]
Messerges, T., Cukier, J., Kevenaar, T., Puhl, L., Struik,
R., and E. Callaway, "Low-Power Security for Wireless
Sensor Networks", in Proceedings of the 1st ACM Workshop
on Security of Ad Hoc and Sensor Networks, Fairfax, VA,
USA, pp. 1-11, Oct. 31 2003.
[Myagmar2005]
Myagmar, S., Lee, AJ., and W. Yurcik, "Threat Modeling as
a Basis for Security Requirements", in Proceedings of the
Symposium on Requirements Engineering for Information
Security (SREIS'05), Paris, France, pp. 94-102, Aug
29, 2005.
[RFC4593] Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to
Routing Protocols", RFC 4593, October 2006.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2",
RFC 4949, August 2007.
[RFC5548] Dohler, M., Watteyne, T., Winter, T., and D. Barthel,
"Routing Requirements for Urban Low-Power and Lossy
Networks", RFC 5548, May 2009.
[RFC5673] Pister, K., Thubert, P., Dwars, S., and T. Phinney,
"Industrial Routing Requirements in Low-Power and Lossy
Networks", RFC 5673, October 2009.
[Wan2004] Wan, T., Kranakis, E., and PC. van Oorschot, "S-RIP: A
Secure Distance Vector Routing Protocol", in Proceedings
of the 2nd International Conference on Applied
Cryptography and Network Security, Yellow Mountain, China,
pp. 103-119, Jun. 8-11 2004.
Authors' Addresses
Tzeta Tsao (editor)
Eka Systems
20201 Century Blvd. Suite 250
Germantown, Maryland 20874
USA
Email: tzeta.tsao@ekasystems.com
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Roger K. Alexander (editor)
Eka Systems
20201 Century Blvd. Suite 250
Germantown, Maryland 20874
USA
Email: roger.alexander@ekasystems.com
Mischa Dohler (editor)
CTTC
Parc Mediterrani de la Tecnologia, Av. Canal Olimpic S/N
Castelldefels, Barcelona 08860
Spain
Email: mischa.dohler@cttc.es
Vanesa Daza (editor)
Universitat Pompeu Fabra
P/ Circumval.lacio 8, Oficina 308
Barcelona 08003
Spain
Email: vanesa.daza@upf.edu
Angel Lozano (editor)
Universitat Pompeu Fabra
P/ Circumval.lacio 8, Oficina 309
Barcelona 08003
Spain
Email: angel.lozano@upf.edu
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