Routing Over Low-Power and Lossy Networks T. Tsao
Internet-Draft R. Alexander
Intended status: Informational Cooper Power Systems
Expires: April 23, 2014 M. Dohler
CTTC
V. Daza
A. Lozano
Universitat Pompeu Fabra
M. Richardson
Sandelman Software Works
October 20, 2013
A Security Threat Analysis for Routing over Low-Power and Lossy Networks
draft-ietf-roll-security-threats-05
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.
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 in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Considerations on ROLL Security . . . . . . . . . . . . . . . 4
3.1. Routing Assets and Points of Access . . . . . . . . . . . 5
3.2. The ISO 7498-2 Security Reference Model . . . . . . . . . 7
3.3. Issues Specific to or Amplified in LLNs . . . . . . . . . 8
3.4. ROLL Security Objectives . . . . . . . . . . . . . . . . 11
4. Threat Sources . . . . . . . . . . . . . . . . . . . . . . . 12
5. Threats and Attacks . . . . . . . . . . . . . . . . . . . . . 12
5.1. Threats due to failures to Authenticate . . . . . . . . . 13
5.1.1. Node Impersonation . . . . . . . . . . . . . . . . . 13
5.1.2. Dummy Node . . . . . . . . . . . . . . . . . . . . . 13
5.1.3. Node Resource Spam . . . . . . . . . . . . . . . . . 13
5.2. Threats and Attacks on Confidentiality . . . . . . . . . 13
5.2.1. Routing Exchange Exposure . . . . . . . . . . . . . . 14
5.2.2. Routing Information (Routes and Network Topology)
Exposure . . . . . . . . . . . . . . . . . . . . . . 14
6. Threats and Attacks on Integrity . . . . . . . . . . . . . . 15
6.1. Routing Information Manipulation . . . . . . . . . . . . 15
6.2. Node Identity Misappropriation . . . . . . . . . . . . . 15
7. Threats and Attacks on Availability . . . . . . . . . . . . . 16
7.1. Routing Exchange Interference or Disruption . . . . . . . 16
7.2. Network Traffic Forwarding Disruption . . . . . . . . . . 16
7.3. Communications Resource Disruption . . . . . . . . . . . 18
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7.4. Node Resource Exhaustion . . . . . . . . . . . . . . . . 18
8. Countermeasures . . . . . . . . . . . . . . . . . . . . . . . 19
8.1. Confidentiality Attack Countermeasures . . . . . . . . . 19
8.1.1. Countering Deliberate Exposure Attacks . . . . . . . 19
8.1.2. Countering Passive Wiretapping Attacks . . . . . . . 20
8.1.3. Countering Traffic Analysis . . . . . . . . . . . . . 21
8.1.4. Countering Remote Device Access Attacks . . . . . . . 21
8.2. Integrity Attack Countermeasures . . . . . . . . . . . . 22
8.2.1. Countering Unauthorized Modification Attacks . . . . 22
8.2.2. Countering Overclaiming and Misclaiming Attacks . . . 23
8.2.3. Countering Identity (including Sybil) Attacks . . . . 23
8.2.4. Countering Routing Information Replay Attacks . . . . 23
8.2.5. Countering Byzantine Routing Information Attacks . . 24
8.3. Availability Attack Countermeasures . . . . . . . . . . . 25
8.3.1. Countering HELLO Flood Attacks and ACK Spoofing
Attacks . . . . . . . . . . . . . . . . . . . . . . . 25
8.3.2. Countering Overload Attacks . . . . . . . . . . . . . 26
8.3.3. Countering Selective Forwarding Attacks . . . . . . . 27
8.3.4. Countering Sinkhole Attacks . . . . . . . . . . . . . 28
8.3.5. Countering Wormhole Attacks . . . . . . . . . . . . . 28
9. ROLL Security Features . . . . . . . . . . . . . . . . . . . 29
9.1. Confidentiality Features . . . . . . . . . . . . . . . . 30
9.2. Integrity Features . . . . . . . . . . . . . . . . . . . 31
9.3. Availability Features . . . . . . . . . . . . . . . . . . 31
9.4. Key Management . . . . . . . . . . . . . . . . . . . . . 32
9.5. Consideration on Matching Application Domain Needs . . . 32
9.5.1. Security Architecture . . . . . . . . . . . . . . . . 32
9.5.2. Mechanisms and Operations . . . . . . . . . . . . . . 35
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 37
11. Security Considerations . . . . . . . . . . . . . . . . . . . 37
12. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 37
13. References . . . . . . . . . . . . . . . . . . . . . . . . . 38
13.1. Normative References . . . . . . . . . . . . . . . . . . 38
13.2. Informative References . . . . . . . . . . . . . . . . . 38
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 42
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 interfaces (e.g., the housing of a small stick-on switch), or
simply safety considerations (e.g., with gas meters). As a
consequence, the resulting networks are more prone to loss of traffic
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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 threat analysis for securing Routing Over
LLNs (ROLL) through an analysis that starts from the routing basics.
The process requires two steps. First, the analysis will be used to
identify pertinent security issues. The second step is to identify
necessary countermeasures to secure the ROLL protocols. As there are
multiple ways to solve the problem and the specific tradeoffs are
deployment specific, the specific countermeasure to be used is
detailed in applicatbility statements.
This document uses [IS07498-2] model, which includes Authentication,
Access Control, Data Confidentiality, Data Integrity, and Non-
Repudiation but to which Availability is added.
All of this document concerns itself with control plane traffic only.
2. Terminology
This document adopts the terminology defined in [RFC6550], in
[RFC4949], and in [I-D.ietf-roll-terminology].
The terms control plane and forwarding plane are used consistently
with section 1 of [RFC6192].
3. Considerations on ROLL Security
Routing security, in essence, ensures that the routing protocol
operates correctly. It entails implementing measures to ensure
controlled state changes on devices and network elements, both based
on external inputs (received via communications) or internal inputs
(physical security of device itself and parameters maintained by the
device, including, e.g., clock). State changes would thereby involve
not only authorization of injector's actions, authentication of
injectors, and potentially confidentiality of routing data, but also
proper order of state changes through timeliness, since seriously
delayed state changes, such as commands or updates of routing tables,
may negatively impact system operation. A security assesment can
therefore begin with a focus on the assets [RFC4949] that may be the
target of the state changes and the access points in terms of
interfaces and protocol exchanges through which such changes may
occur. In the case of routing security the focus is directed towards
the elements associated with the establishment and maintenance of
network connectivity.
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This section sets the stage for the development of the analysis by
applying the systematic approach proposed in [Myagmar2005] to the
routing security, 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 to the routing functionality.
Next, the [ISO.7498-2.1988] security model is briefly described.
Then, consideration is given to issues specific to or amplified in
LLNs. This section concludes with the formulation of a set of
security objectives for ROLL.
3.1. Routing Assets and Points of Access
An asset is an important system resource (including information,
process, or physical resource), the access to, corruption or loss of
which adversely affects the system. In the control plane context, an
asset is information about the network, processes used to manage and
manipulate this data, and the physical devices on which this data is
stored and manipulated. The corruption or loss of these assets may
adversely impact the control plane of the network. Within the same
context, a point of access is an interface or protocol that
facilitates interaction between control plane components.
Identifying these assets and points of access will provide a basis
for enumerating the attack surface of the control plane.
A level-0 data flow diagram [Yourdon1979] is used here to identify
the assets and points of access within a generic routing process.
The use of a data flow diagram allows for a clear and concise model
of the way in which routing nodes interact and process information,
and hence provides a context for threats and attacks. The goal of
the model is to be as detailed as possible so that corresponding
assets, points of access, and process in an individual routing
protocol can be readily identified.
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.
...................................................
: :
: :
|Node_i|<------->(Routing Neighbor _________________ :
: Discovery)------------>Neighbor Topology :
: -------+--------- :
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: | :
|Node_j|<------->(Route/Topology +--------+ :
: Exchange) | :
: | V ______ :
: +---->(Route Generation)--->Routes :
: ---+-- :
: | :
: Routing on a Node Node_k | :
...................................................
|
|Forwarding |
|On Node_l|<-------------------------------------------+
Notation:
(Proc) A process Proc
________
topology A structure storing neighbor adjacency (parent/child)
--------
________
routes A structure storing the forwarding information base (FIB)
--------
|Node_n| An external entity Node_n
-------> Data flow
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;
* route generation process;
* 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 threat analysis is to be comprehensive. Hence, some of
the discussion which follows is associated with assets and points of
access that are not directly related to routing protocol design but
nonetheless provided for reference since they do have direct
consequences on the security of routing.
3.2. The ISO 7498-2 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 authentication, access control, data
confidentiality, data integrity, and non-repudiation. In the context
of ROLL
Authentication
Authentication involves the mutual authentication of the
routing peers prior to exchanging route information (i.e., peer
authentication) as well as ensuring that the source of the
route data is from the peer (i.e., data origin authentication).
[RFC5548] points out that LLNs can be drained by
unauthenticated peers before configuration. [RFC5673] requires
availability of open and untrusted side channels for new
joiners, and it requires strong and automated authentication so
that networks can automatically accept or reject new joiners.
Access Control
Access Control provides protection against unauthorized use of
the asset, and deals with the authorization of a node.
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
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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 entails the protection of routing information and
routing neighbor maintenance exchanges, as well as derived
information maintained in the database, from unauthorized
modification, insertions, deletions or replays. to be addressed
beyond the routing protocol.
Non-repudiation
Non-repudiation is the assurance that the transmission and/or
reception of a message cannot later be denied. The service of
non-repudiation applies after-the-fact and thus relies on the
logging or other capture of on-going message exchanges and
signatures. Applied to routing, non-repudiation is not an
issue because it does not apply to routing protocols, which are
machine-to-machine protocols. Further, with the LLN
application domains as described in [RFC5867] and [RFC5548],
proactive measures are much more critical than retrospective
protections. Finally, given the significant practical limits
to on-going routing transaction logging and storage and
individual device digital signature verification for each
exchange, non-repudiation in the context of routing is an
unsupportable burden that bears no further considered as a ROLL
security issue.
It is recognized that, besides those security issues captured in the
ISO 7498-2 model, availability, is a security requirement:
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 should be emphasized here that for ROLL security the above
requirements must be complemented by the proper security policies and
enforcement mechanisms to ensure that security objectives are met by
a given ROLL implementation.
3.3. Issues Specific to or Amplified in LLNs
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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.
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. The chosen security
mechanisms also needs to work within these constraints.
Synchronization of security states with sleepy nodes is yet
another issue.
Large scale of rolled out network
The possibly numerous nodes to be deployed make manual on-site
configuration unlikely. For example, an urban deployment can
see several hundreds of thousands of nodes being installed by
many installers with a low level of expertise. Nodes may be
installed and not activated for many years, and additional
nodes may be added later on, which may be from old inventory.
The lifetime of the network is measured in decades, and this
complicates the operation of key management.
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 as a higher valued attack target. In
fact, when Point-to-MultiPoint (P2MP) and MultiPoint-to-Point
(MP2P) traffic represents a majority of the traffic, routing
attacks consisting of advertising incorrect preferred routes
can cause serious damage.
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While it might seem that nodes higher up in the cyclic graph
(i.e. those with lower rank) should be secured in a stronger
fashion, it is not in general easy to predict which nodes will
occupy those positions until after deployment. Issues of
redundancy and inventory control suggests that any node might
wind up in such a sensitive attack position, so all nodes need
to be equally secure.
In addition, even if it were possible to predict which nodes
will occupy positions of lower rank and provision them with
stronger security mechanisms, in the absense of a strong
authorization model, any node could advertise an incorrect
preferred route.
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 limited number of applications require
the support of mobile nodes, e.g., a home LLN that includes
nodes on wearable health care devices or an industry LLN that
includes nodes on cranes and vehicles. On the other hand, if a
routing protocol is indeed used in such applications, it will
clearly need to have corresponding security mechanisms.
Additionally nodes may appear to move from one side of a wall
to another without any actual motion involved, the result of
changes to electromagnetic properties, such as opening and
closing of a metal door.
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.
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The above list considers how an LLN's physical constraints, size,
operations, and variety of application areas may impact security.
However, it is the combinations of these factors that particularly
stress the security concerns. For instance, securing routing for a
large number of autonomous devices that are left in unattended
locations with limited physical security presents challenges that are
not found in the common circumstance of administered networked
routers. The following subsection sets up the security objectives
for the routing protocol designed by the ROLL WG.
3.4. ROLL Security Objectives
This subsection applies the ISO 7498-2 model to routing assets and
access points, taking into account the LLN issues, to develop a set
of ROLL security objectives.
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 iintegrity remains intact during
transfer and in storage;
o routing/topology information is used by authorized entities;
o routing/topology information is available when needed.
In conjunction, it is necessary to be assured that
o authorized peers authenticate themselves during the routing
neighbor discovery process;
o the routing/topology information received is 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 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.
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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. Threat Sources
[RFC4593] provides a detailed review of the threat sources: outsiders
and byzantine. ROLL has the same threat sources.
5. Threats and Attacks
This section outlines general categories of threats under the ISO
7498-2 model and highlights the specific attacks in each of these
categories for ROLL. As defined in [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 the attacks that
can cause security breaches under the ISO 7498-2 model to the routing
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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 source of the attacks is assumed to be from either
inside or outside attackers. The capability these attackes may be
limited to node-equivalent, but also to more sophisticated computing
platforms.
5.1. Threats due to failures to Authenticate
5.1.1. Node Impersonation
If an attacker can join a network with any identify, then it may be
able to assume the role of a legitimate (and existing node). It may
be able to report false readings (in metering applications), or
provide inappropriate control messages (in control systems involving
actuators) if the security of the application is leveraged from the
security of the routing system.
In other systems where there is separate application layer security,
the ability to impersonate a node would permit an attacker to direct
traffic to itself, which facilitates on-path attacks including
replaying, delaying, or duplicating control messages.
5.1.2. Dummy Node
If an attacker can join a network with any identify, then it can
pretend to be a legitimate node, receiving any service legitimate
nodes receive. It may also be able to report false readings (in
metering applications), or provide inappropriate authorizations (in
control systems involving actuators), or perform any other attacks
that are facilitated by being able to direct traffic towards itself.
5.1.3. Node Resource Spam
If an attacker can join a network with any identify, then it can
continously do so, draining down the resources of the network to
store identity and routing information, potentionally forcing
legitimate nodes of the network.
5.2. Threats and Attacks on Confidentiality
The assessment in Section 3.2 indicates that there are threat actions
against the confidentiality of routing information at all points of
access. The confidentiality threat consequences is disclosure, see
Section 3.1.2 of [RFC4593]. For ROLL this is the disclosure of
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routing information either by evesdropping on the communication
exchanges between routing nodes or by direct access of node's
information.
5.2.1. 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 routing exchanges will contain reachability information, which
would identify the relative importance of different nodes in the
network. Nodes higher up in the DODAG, to which more streams of
information flow, would be more interesting targets for other
attacks, and routing exchange exposures can identify them.
5.2.2. 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 attachers to gain direct
access to the configuration and connectivity of the network thereby
exposing routing to targeted attacks on key nodes or links. Since
routes and neighbor topology information is stored within the node
device, threats or attacks on the confidentiality of the information
will apply to the physical device including specified and unspecified
internal and external interfaces.
The forms of attack that allow unauthorized access or disclosure 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).
Both of these attack vectors are considered a device specific issue,
and are out of scope for the RPL protocol to defend against. In some
applications, physical device compromise may be a real threat and it
may be necessary to provide for other devices to react quickly to
exclude a compromised device.
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6. 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.
6.1. 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 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.
A sub-optimal network may use too much power and/or may congest some
routes leading to premature failure of a node, and a denial of
service on the entire network.
In addition, 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.
6.2. Node Identity Misappropriation
Falsification or misappropriation of node identity between routing
participants opens the door for other attacks; it can also cause
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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.
7. Threats and Attacks on Availability
The assessment in Section 3.2 indicates that the process and
resources assets are exposed to threats against availability; attacks
in this category may exploit directly or indirectly information
exchange or forwarding (see [RFC4732] for a general discussion).
7.1. Routing Exchange Interference or Disruption
Interference is the threat action and disruption is threat
consequence that allows attackers to influence the operation and
convergence of the routing protocols by impeding the routing
information exchange.
The forms of attack that allow interference or disruption of routing
exchange include:
o Routing information replay;
o ACK spoofing;
o Overload attacks. (Section 8.3.2)
In addition, attacks may also be directly conducted at the physical
layer in the form of jamming or interfering.
7.2. Network Traffic Forwarding Disruption
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The disruption of the network traffic forwarding capability will
undermine the central function of network routers and the ability to
handle user traffic. This affects the availability of the network
because of the potential to impair the primary capability of the
network.
In addition to physical layer obstructions, the forms of attack that
allows disruption of network traffic forwarding include [Karlof2003]
o Selective forwarding attacks;
|Node_1|--(msg1|msg2|msg3)-->|Attacker|--(msg1|msg3)-->|Node_2|
(a) Selective Forwarding
Figure 2: Selective Forwarding
o Wormhole attacks;
|Node_1|-------------Unreachable---------x|Node_2|
| ^
| Private Link |
'-->|Attacker_1|===========>|Attacker_2|--'
(b) Wormhole
Figure 3: Wormhole Attacks
o Sinkhole attacks.
|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
,-------' |
| |
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|Node_3| |Node_i|
(c) Sinkhole
Figure 4: Selective Forwarding, Wormhole, and Sinkhole Attacks
These attacks are generally done to both control plane and forwarding
plane traffic. A system that prevents control plane traffic (RPL
messages) from being diverted in these ways will also prevent actual
data from being diverted.
7.3. 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
directly addressed within the underlying subsystem and its
implemented protocol layers.
7.4. Node Resource Exhaustion
A potential threat consequence can arise from attempts to overload
the node resource asset by initiating exchanges that can lead to the
exhaustion of processing, memory, or energy resources. The
establishment and maintenance of routing neighbors opens the routing
process to engagement and potential acceptance of multiple
neighboring peers. Association information must be stored for each
peer entity and for the wireless network operation provisions made to
periodically update and reassess the associations. An introduced
proliferation of apparent routing peers can therefore have a negative
impact on node resources.
Node resources may also be unduly consumed by attackers attempting
uncontrolled topology peering or routing exchanges, routing replays,
or the generating of other data traffic floods. Beyond the
disruption of communications channel resources, these consequences
may be able to exhaust node resources only where the engagements are
able to proceed with the peer routing entities. Routing operation
and network forwarding functions can thus be adversely impacted by
node resources exhaustion that stems from attacks that include:
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o Identity (including Sybil) attacks;
o Routing information replay attacks;
o HELLO flood attacks;
o Overload attacks. (Section 8.3.2)
8. Countermeasures
By recognizing the characteristics of LLNs that may impact routing,
this analysis provides the basis for developing capabilities within
ROLL protocols to deter the identified attacks and mitigate the
threats. The following subsections consider such countermeasures by
grouping the attacks according to the classification of the ISO
7498-2 model so that associations with the necessary security
services are more readily visible. However, the considerations here
are more systematic than confined to means available only within
routing; the next section will then distill and make recommendations
appropriate for a secured ROLL protocol.
8.1. Confidentiality Attack Countermeasures
Attacks to disclosure routing information may be mounted at the level
of the routing information assets, at the points of access associated
with routing exchanges between nodes, or through device interface
access. To gain access to routing/topology information, the attacker
may rely on a compromised node that deliberately exposes the
information during the routing exchange process, may rely on passive
wiretapping or traffic analysis, or may attempt access through a
component or device interface of a tampered routing node.
8.1.1. 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.
A prerequisite to countering this attack is to ensure that the
communicating nodes are authenticated prior to data encryption
applied in the routing exchange. Authentication ensures that the
nodes are who they claim to be even though it does not provide an
indication of whether the node has been compromised.
To mitigate the risk of deliberate exposure, the process that
communicating nodes use to establish session keys must be peer-to-
peer (i.e., between the routing initiating and responding nodes).
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This helps ensure that neither node is exchaning routing information
with another peer without the knowledge of both communicating
peerscan. For a deliberate exposure attack to succeed, the comprised
node will need to more overt and take independent actions in order to
disclose the routing information to 3rd party.
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.
8.1.2. Countering Passive Wiretapping Attacks
A passive wiretap attack seeks to breach routing confidentiality
through passive, direct analysis and processing of the information
exchanges between nodes.
Passive wiretap attacks can be directly countered through the use of
data encryption for all routing exchanges. Only when a validated and
authenticated node association is completed will routing exchange be
allowed to proceed using established session keys and an agreed
encryption algorithm. The strength of the encryption algorithm and
session key sizes will determine the minimum requirement for an
attacker mounting this passive security attack. The possibility of
incorporating options for security level and algorithms is further
considered in Section 9.5. Because of the resource constraints of
LLN devices, symmetric (private) key encryption will provide the best
trade-off in terms of node and channel resource overhead and the
level of security achieved. This will of course not preclude the use
of asymmetric (public) key encryption during the session key
establishment phase.
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
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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.
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.
8.1.3. 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 an LLN, especially one
founded on shared medium, is passive and relies on the ability to
read the immutable source/destination layer-3 routing information
that must remain unencrypted to permit network routing.
One way in which passive traffic analysis attacks can be muted is
through the support of load balancing that allows traffic to a given
destination to be sent along diverse routing paths. Where the
routing protocol supports load balancing along multiple links at each
node, the number of routing permutations in a wide area network
surges thus increasing the cost of traffic analysis. ROLL does not
generally support multi-path routing within a single DODAG. Multiple
DODAGs are supported in the protocol, but few deployments will have
space for more than half a dozen, and there are at present no clear
ways to multiplex traffic for a single application across multiple
DODAGs.
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.
The only means of fully countering a traffic analysis attack is
through the use of tunneling (encapsulation) where encryption is
applied across the entirety of the original packet source/destination
addresses. Deployments which use layer-2 security that includes
encryption already do this for all traffic.
8.1.4. 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
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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.
8.2. 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.
8.2.1. 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.
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8.2.2. 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;
o designs which restrict realizable network topologies.
8.2.3. 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
explicitly or implicitly an asset to an application running on the
LLN, for example, the LBR in a P2MP or MP2P LLN.
8.2.4. Countering Routing Information Replay Attacks
In many routing protocols, message replay can result in false
topology and/or routes. This is often counted with some kind of
counter to ensure the freshness of the message. Replay of a current,
literal RPL message are in general idempotent to the topology. An
older (lower DODAGVersionNumber) message, if replayed would be
rejected as being stale. The trickle algorithm further dampens the
affect of any such replay, as if the message was current, then it
would contain the same information as before, and it would cause no
network changes.
Replays may well occur in some radio technologies (not very likely,
802.15.4) as a result of echos or reflections, and so some replays
must be assumed to occur naturally.
Note that for there to be no affect at all, the replay must be done
with the same apparent power for all nodes receiving the replay. A
change in apparent power might change the metrics through changes to
the ETX and therefore might affect the routing even though the
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contents of the packet were never changed. Any replay which appears
to be different should be analyzed as a Selective Forwarding Attack,
Sinkhole Attack or Wormhole Attack.
8.2.5. Countering Byzantine Routing Information Attacks
Where a node is captured or compromised but continues to operate for
a period with valid network security credentials, the potential
exists for routing information to be manipulated. This compromise of
the routing information could thus exist in spite of security
countermeasures that operate between the peer routing devices.
Consistent with the end-to-end principle of communications, such an
attack can only be fully addressed through measures operating
directly between the routing entities themselves or by means of
external entities able to access and independently analyze the
routing information. Verification of the authenticity and liveliness
of the routing entities can therefore only provide a limited counter
against internal (Byzantine) node attacks.
For link state routing protocols where information is flooded with,
for example, areas (OSPF [RFC2328]) or levels (ISIS [RFC1142]),
countermeasures can be directly applied by the routing entities
through the processing and comparison of link state information
received from different peers. By comparing the link information
from multiple sources decisions can be made by a routing node or
external entity with regard to routing information validity; see
Chapter 2 of [Perlman1988] for a discussion on flooding attacks.
For distance vector protocols where information is aggregated at each
routing node it is not possible for nodes to directly detect
Byzantine information manipulation attacks from the routing
information exchange. In such cases, the routing protocol must
include and support indirect communications exchanges between non-
adjacent routing peers to provide a secondary channel for performing
routing information validation. S-RIP [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
analysis, any protection against Byzantine routing information
attacks will need to be directly included within the mechanisms of
the ROLL routing protocol.
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8.3. Availability Attack Countermeasures
As alluded to before, availability requires that routing information
exchanges and forwarding mechanisms be available when needed so as to
guarantee 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 8.2.3 and
Section 8.2.4, respectively.
8.3.1. 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 an LLN.
They essentially lead nodes to believe that suitable routes are
available even though they are not and hence constitute a serious
availability attack.
A HELLO attack mounted against RPL would involve sending out (or
replaying) DIO messages by the attacker. Lower power LLN nodes might
then attempt to join the DODAG at a lower rank than they would
otherwise.
The most effective method from [I-D.suhopark-hello-wsn] is the verify
bidirectionality. A number of layer-2 links are arranged in
controller/spoke arrangements, and continuously are validating
connectivity at layer 2.
In addition, in order to calculate metrics, the ETX must be computed,
and this involves, in general, sending a number of messages between
nodes which are believed to be adjacent.
[I-D.kelsey-intarea-mesh-link-establishment] is one such protocol.
In order to join the DODAG, a DAO message is sent upwards. In RPL
the DAO is acknowledged by the DAO-ACK message. This clearly checks
bidirectionality at the control plane.
As discussed in section 5.1, [I-D.suhopark-hello-wsn] a receiver with
a sensitive receiver could well hear the DAOs, and even send DAO-ACKs
as well. Such a node is a form of WormHole attack.
These attacks are also all easily defended against using either
layer-2 or layer-3 authentication. Such an attack could only be made
against a completely open network (such as might be used for
provisioning new nodes), or by a compromised node.
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8.3.2. 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 store more quickly, when the nodes rely on batteries or
energy scavenging. It thus significantly shortens the lifetime of
networks of energy-constrained nodes and constitutes another serious
availability attack.
With energy being one of the most precious assets of LLNs, targeting
its availability is a fairly obvious attack. Another way of
depleting the energy of an LLN node is to have the malicious node
overload the network with irrelevant traffic. This impacts
availability since certain routes get congested which:
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 battery and energy scavenging nodes more quickly 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 based
on system operation characteristics;
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 at the network layer once it has been detected
that more traffic is injected into the network than allowed by a
prior set or dynamically adjusted threshold. Finally, if
communication is sufficiently secured, only trusted nodes can receive
and forward traffic which also lowers the risk of an overload attack.
Receiving nodes that validate signatures and sending nodes that
encrypt messages need to be cautious of cryptographic processing
usage when validating signatures and encrypting messages. Where
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feasible, certificates should be validated prior to use of the
associated keys to counter potential resource overloading attacks.
The associated design decision needs to also consider that the
validation process requires resources and thus itself could be
exploited for attacks. Alternatively, resource management limits can
be placed on routing security processing events (see the comment in
Section 6, paragraph 4, of [RFC5751]).
8.3.3. Countering Selective Forwarding Attacks
Selective forwarding attacks are a form of DoS attack which impacts
the availability of the generated routing paths.
A selective forwarding attack may be done by a node involved with the
routing process, or it may be done by what otherwise appears to be a
passive antenna or other RF feature or device, but is in fact an
active (and selective) device. An RF antenna/repeater which is not
selective, is not a threat.
An insider malicious node basically blends neatly in with the network
but then may decide to forward and/or manipulate certain packets. If
all packets are dropped, then this attacker is also often referred to
as a "black hole". Such a form of attack is particularly dangerous
if coupled with sinkhole attacks since inherently a large amount of
traffic is attracted to the malicious node and thereby causing
significant damage. In a shared medium, an outside malicious node
would selectively jam overheard data flows, where the thus caused
collisions incur selective forwarding.
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 selecting 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 a method is inherently suboptimal from an energy
consumption point of view; it is also suboptimal from a network
utilization perspective. The second method basically involves a
constantly changing routing topology in that next-hop routers are
chosen from a dynamic set in the hope that the number of malicious
nodes in this set is negligible. A routing protocol that allows for
disjoint routing paths may also be useful.
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8.3.4. 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 [Karlof2003]. 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.
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.
Some LLNs may provide for geolocation services, often derived from
solving triangulation equations from radio delay calculations, such
calculations could in theory be subverted by a sinkhole that
transmitted at precisely the right power in a node to node fashion.
While geographic knowledge could help assure that traffic always went
in the physical direction desired, it would not assure that the
traffic was taking the most efficient route, as the lowest cost real
route might be match the physical topology; such as when different
parts of an LLN are connected by high-speed wired networks.
8.3.5. Countering Wormhole Attacks
In wormhole attacks at least two malicious nodes claim to have a
short path between themselves [Karlof2003]. This changes the
availability of certain routing paths and hence constitutes a serious
security breach.
Essentially, two malicious insider nodes use another, more powerful,
transmitter to communicate with each other and thereby distort the
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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".
A pure Wormhole attack is nearly impossible to detect. A wormhole
which is used in order to subsequently mount another kind of attack
would be defeated by defeating the other attack. A perfect wormhole,
in which there is nothing adverse that occurs to the traffic, would
be difficult to call an attack. The worst thing that a benign
wormhole can do in such a situation is to cease to operate (become
unstable), causing the network to have to recalculate routes.
A highly unstable wormhole is no different than a radio opaque (i.e.
metal) door that opens and closes a lot. RPL includes hystersis in
its objective functions [RFC6719] in an attempt to deal with frequent
changes to the ETX between nodes.
9. ROLL Security Features
The assessments and analysis in Section 5 examined all areas of
threats and attacks that could impact routing, and the
countermeasures presented in Section 8 were reached without confining
the consideration to means only available to routing. This section
puts the results into perspective and provides a framework for
addressing the derived set of security objectives that must be met by
the routing protocol(s) specified by the ROLL Working Group. It
bears emphasizing that the target here is a generic, universal form
of the protocol(s) specified and the normative keywords are mainly to
convey the relative level of importance or urgency of the features
specified.
In this view, 'MUST' is used to define the requirements that are
specific to the routing protocol and that are essential for an LLN
routing protocol to ensure that routing operation can be maintained.
Adherence to MUST requirements is needed to directly counter attacks
that can affect the routing operation (such as those that can impact
maintained or derived routing/forwarding tables). 'SHOULD' is used
to define requirements that counter indirect routing attacks where
such attacks do not of themselves affect routing but can assist an
attacker in focusing its attack resources to impact network operation
(such as DoS targeting of key forwarding nodes). 'MAY' covers
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optional requirements that can further enhance security by increasing
the space over which an attacker must operate or the resources that
must be applied. While in support of routing security, where
appropriate, these requirements may also be addressed beyond the
network routing protocol at other system communications layers.
The first part of this section, Section 9.1 to Section 9.3, 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 an LLN system, the actual strength of the security
services afforded to it should be made to conform to each system's
security policy; how a design may address the needs of the urban,
industrial, home automation, and building automation application
domains also needs to be considered. The second part of this
section, Section 9.4 and Section 9.5, discusses system security
aspects that may impact routing but that also require considerations
beyond the routing protocol, as well as potential approaches.
If an LLN employs multicast and/or anycast, these alternative
communications modes MUST be secured with the same routing security
services specified in this section. Furthermore, irrespective of the
modes of communication, nodes MUST provide adequate physical tamper
resistance commensurate with the particular application domain
environment to ensure the confidentiality, integrity, and
availability of stored routing information.
9.1. Confidentiality Features
With regard to confidentiality, protecting the routing/topology
information from unauthorized disclosure is not directly essential to
maintaining the routing function. Breaches of confidentiality may
lead to other attacks or the focusing of an attacker's resources (see
Section 5.2) but does not of itself directly undermine the operation
of the routing function. However, to protect against, and reduce
consequences from other more direct attacks, routing information
should be protected. Thus, a secured ROLL protocol:
o MUST implement payload encryption;
o MAY provide tunneling;
o MAY provide load balancing.
Where confidentiality is incorporated into the routing exchanges,
encryption algorithms and key lengths need to be specified in
accordance with the level of protection dictated by the routing
protocol and the associated application domain transport network. In
terms of the life time of the keys, the opportunity to periodically
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change the encryption key increases the offered level of security for
any given implementation. However, where strong cryptography is
employed, physical, procedural, and logical data access protection
considerations may have more significant impact on cryptoperiod
selection than algorithm and key size factors. Nevertheless, in
general, shorter cryptoperiods, during which a single key is applied,
will enhance security.
Given the mandatory protocol requirement to implement routing node
authentication as part of routing integrity (see Section 9.2), 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 complement to the key
length and encryption algorithm required for a given application
domain. For LLNs, the coordination of confidentiality key management
with the implementation of node device authentication can thus reduce
the overhead associated with supporting data confidentiality. If a
new ciphering key is concurrently generated or updated in conjunction
with the mandatory authentication exchange occurring with each
routing peer association, signaling exchange overhead can be reduced.
9.2. 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, RPL must either run using only the Secure
versions of the messages, or must run over a layer-2 that uses
channel binding between node identity and transmissions. (i.e.: a
layer-2 which has an identical network-wide transmission key can not
defend against many attacks)
XXX. Logging is critical, but presently impossible.
9.3. 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 9.5). 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;
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o MAY choose randomly if multiple paths are available;
o MAY set quotas to limit transmit or receive volume;
o MAY use geographic information for flow control.
9.4. Key Management
The functioning of the routing security services requires keys and
credentials. Therefore, even though not directly a ROLL security
requirement, an LLN MUST have a process for initial key and
credential configuration, as well as secure storage within the
associated devices. Anti-tampering SHOULD be a consideration in
physical design. Beyond initial credential configuration, an LLN is
also encouraged to have automatic procedures for the revocation and
replacement of the maintained security credentials.
While RPL has secure modes, but some modes are impractical without
use of public key cryptography believed to be too expensive by many.
RPL layer-3 security will often depend upon existing LLN layer-2
security mechanisms, which provides for node authentication, but
little in the way of node authorization.
9.5. Consideration on Matching Application Domain Needs
Providing security within an LLN requires considerations that extend
beyond routing security to the broader LLN application domain
security implementation. In other words, as routing is one component
of an LLN system, the actual strength of the implemented security
algorithms for the routing protocol MUST be made to conform to the
system's target level of security. The development so far takes into
account collectively the impacts of the issues gathered from
[RFC5548], [RFC5673], [RFC5826], and [RFC5867]. The following two
subsections first consider from an architectural perspective how the
security design of a ROLL protocol may be made to adapt to the four
application domains, and then examine mechanisms and protocol
operations issues.
9.5.1. Security Architecture
The first challenge for a ROLL protocol security design is to have an
architecture that can adequately address a set of very diverse needs.
It is mainly a consequence of the fact that there are both common and
non-overlapping requirements from the four application domains,
while, conceivably, each individual application will present yet its
own unique constraints.
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For a ROLL protocol, the security requirements defined in Section 9.1
to Section 9.4 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 part of the 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 independently of the lower layers.
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 network, security measures implemented as part of the routing
protocol will be redundant to security measures implemented elsewhere
as part of the protocol stack.
Security mechanisms built into the routing protocol can ensure that
all desired countermeasures can be directly addressed by the protocol
all the way to the endpoint of the routing exchange. In particular,
routing protocol Byzantine attacks by a compromised node that retains
valid network security credentials can only be detected at the level
of the information exchanged within the routing protocol. Such
attacks aimed at the manipulation of the routing information can only
be fully addressed through measures operating directly between the
routing entities themselves or external entities able to access and
analyze the routing information (see discussion in Section 8.2.5).
On the other hand, it is more desirable from an LLN device
perspective that the ROLL protocol is integrated into the framework
of an overall system architecture where the security facility may be
shared by different applications and/or across layers for efficiency,
and where security policy and configurations can be consistently
specified. See, for example, considerations made in RIPng [RFC2080]
or the approach presented in [Messerges2003].
Where the routing protocol is able to rely on security measures
configured within other layers of the protocol stack, greater system
efficiency can be realized by avoiding potentially redundant
security. Relying on an open trust model [Messerges2003], the
security requirements of the routing protocol can be more flexibly
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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.
For example, where a given security encryption scheme is deemed the
appropriate standard for network confidentiality of data exchanges at
the link layer, that level of security is directly provided to
routing protocol exchanges across the local link. Similarly, where a
given authentication procedure is stipulated as part of the standard
required for authenticating network traffic, that security provision
can then meet the requirement needed for authentication of routing
exchanges. In addition, in the context of the different LLN
application domains, the level of security specified for routing can
and should be consistent with that considered appropriate for
protecting the network within the given environment.
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 attackers that can affect the validity of the
information content exchanged between routing entities can only be
directly countered at the routing protocol level, the ROLL protocol
MAY support mechanisms for verifying routing data validity that
extend beyond the chain of trust created through device
authentication. This protocol-specific security mechanism SHOULD be
made optional within the protocol allowing it to be invoked according
to the given routing protocol and application domain and as selected
by the system user. All other ROLL security mechanisms needed to
meet the above identified routing security requirements can be
flexibly implemented within the transport network (at the IP network
layer or higher or lower protocol layers(s)) according to the
particular application domain and user network configuration.
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Based on device capabilities and the spectrum of operating
environments it would be difficult for a single fixed security design
to be applied to address the diversified needs of the urban,
industrial, home, and building ROLL application domains, and
foreseeable others, without forcing a very low common denominator set
of requirements. On the other hand, providing four individual domain
designs that attempt to a priori match each individual domain is also
very unlikely to provide a suitable answer given the degree of
network variability even within a given domain; furthermore, the type
of link layers in use within each domain also influences the overall
security.
Instead, the framework implementation approach recommended is for
optional, routing protocol-specific measures that can be applied
separately from, or together with, flexible transport network
mechanisms. Protocol-specific measures include the specification of
valid parameter ranges, increments and/or event frequencies that can
be verified by individual routing devices. In addition to deliberate
attacks this allows basic protocol sanity checks against
unintentional mis-configuration. Transport network mechanisms would
include out-of-band communications that may be defined to allow an
external entity to request and process individual device information
as a means to effecting an external verification of the derived
network routing information to identify the existence of intentional
or unintentional network anomalies.
This approach allows countermeasures against byzantine attackers to
be applied in environments where applicable threats exist. At the
same time, it allows routing protocol security to be supported
through measures implemented within the transport network that are
consistent with available system resources and commensurate and
consistent with the security level and strength applied in the
particular application domain networks.
9.5.2. Mechanisms and Operations
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With an architecture allowing different configurations to meet the
application domain needs, the task is then to find suitable
mechanisms. For example, one of the main problems of synchronizing
security states of sleepy nodes lies in difficulties in
authentication; these nodes may not have received in time the most
recent update of security material. Similarly, the issues of minimal
manual configuration, prolonged rollout and delayed addition of
nodes, and network topology changes also complicate security
management. In many cases the ROLL protocol may need to bootstrap
the authentication process and allow for a flexible expiration scheme
of authentication credentials. This exemplifies the need for the
coordination and interoperation between the requirements of the ROLL
routing protocol and that of the system security elements.
Similarly, the vulnerability brought forth by some special-function
nodes, e.g., LBRs requires the assurance, particularly, of the
availability of communication channels and node resources, or that
the neighbor discovery process operates without undermining routing
availability.
There are other factors which are not part of a ROLL routing protocol
but which can still affect its operation. These include elements
such as weaker barrier to accessing the data or security material
stored on the nodes through physical means; therefore, the internal
and external interfaces of a node need to be adequate for guarding
the integrity, and possibly the confidentiality, of stored
information, as well as the integrity of routing and route generation
processes.
Figure 5 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.
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|
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---Interface | | Interface---
| ...................................... |
| : | | : |
| : +-----+----+ +----+-----+ : |
| : |Transport/| |Transport/| : |
____v___ : +>|Network | |Network |<+ : ___v____
/ \ : | +-----+----+ +----+-----+ | : / \
| |-:-+ | | +-:-| |
|Security| : +-----+----+ +----+-----+ : |Security|
+->|Services|-:-->| Link | | Link |<--:-|Services|<-+
| |Entity | : +-----+----+ +----+-----+ : |Entity | |
| | |-:-+ | | +-:-| | |
| \________/ : | +-----+----+ +----+-----+ | : \________/ |
| : +>| Physical | | Physical |<+ : |
Application : +-----+----+ +----+-----+ : Application
Domain User : | | : Domain User
Configuration : |__Comm. Channel_| : Configuration
: :
...Protocol Stack.....................
Figure 5: LLN Device Security Model
10. IANA Considerations
This memo includes no request to IANA.
11. Security Considerations
The analysis presented in this document provides security analysis
and design guidelines with a scope limited to ROLL. Security
services are identified as requirements for securing ROLL. The
specific mechanisms to be used to deal with each threat is specified
in link-layer and deployment specific applicability statements.
12. Acknowledgments
The authors would like to acknowledge the review and comments from
Rene Struik and JP Vasseur. The authors would also like to
acknowledge the guidance and input provided by the ROLL Chairs, David
Culler, and JP Vasseur, and the Area Director Adrian Farrel.
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This document started out as a combined threat and solutions
document. As a result of security review, the document was split up
by ROLL co-Chair Michael Richardson and security Area Director Sean
Turner as it went through the IETF publication process. The
solutions to the threads are application and layer-2 specific, and
have therefore been moved to the relevant applicability statements.
Ines Robles kept track of the many issues that were raised during the
development of this document
13. References
13.1. Normative References
[I-D.ietf-roll-terminology]
Vasseur, J., "Terminology in Low power And Lossy
Networks", draft-ietf-roll-terminology-04 (work in
progress), September 2010.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4107] Bellovin, S. and R. Housley, "Guidelines for Cryptographic
Key Management", BCP 107, RFC 4107, June 2005.
[RFC4301] Kent, S. and K. Seo, "Security Architecture for the
Internet Protocol", RFC 4301, December 2005.
[RFC6550] Winter, T., Thubert, P., Brandt, A., Hui, J., Kelsey, R.,
Levis, P., Pister, K., Struik, R., Vasseur, JP., and R.
Alexander, "RPL: IPv6 Routing Protocol for Low-Power and
Lossy Networks", RFC 6550, March 2012.
[RFC6719] Gnawali, O. and P. Levis, "The Minimum Rank with
Hysteresis Objective Function", RFC 6719, September 2012.
13.2. Informative References
[FIPS197] , "Federal Information Processing Standards Publication
197: Advanced Encryption Standard (AES)", US National
Institute of Standards and Technology, Nov. 26 2001.
[Huang2003]
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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.alexander-roll-mikey-lln-key-mgmt]
Alexander, R. and T. Tsao, "Adapted Multimedia Internet
KEYing (AMIKEY): An extension of Multimedia Internet
KEYing (MIKEY) Methods for Generic LLN Environments",
draft-alexander-roll-mikey-lln-key-mgmt-04 (work in
progress), September 2012.
[I-D.kelsey-intarea-mesh-link-establishment]
Kelsey, R., "Mesh Link Establishment", draft-kelsey-
intarea-mesh-link-establishment-05 (work in progress),
February 2013.
[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.
[IEEE1149.1]
, "IEEE Standard Test Access Port and Boundary Scan
Architecture", IEEE-SA Standards Board, Jun. 14 2001.
[ISO.7498-2.1988]
International Organization for Standardization,
"Information Processing Systems - Open Systems
Interconnection Reference Model - Security Architecture",
ISO Standard 7498-2, 1988.
[Karlof2003]
Karlof, C. and D. Wagner, "Secure routing in wireless
sensor networks: attacks and countermeasures", Elsevier
AdHoc Networks Journal, Special Issue on Sensor Network
Applications and Protocols, 1(2):293-315, September 2003.
[Kasumi3gpp]
, "3GPP TS 35.202 Specification of the 3GPP
confidentiality and integrity algorithms; Document 2:
Kasumi specification", 3GPP TSG SA3, 2009.
[Messerges2003]
Messerges, T., Cukier, J., Kevenaar, T., Puhl, L., Struik,
R., and E. Callaway, "Low-Power Security for Wireless
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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.
[Perlman1988]
Perlman, N., "Network Layer Protocols with Byzantine
Robustness", MIT LCS Tech Report, 429, 1988.
[RFC1142] Oran, D., "OSI IS-IS Intra-domain Routing Protocol", RFC
1142, February 1990.
[RFC2080] Malkin, G. and R. Minnear, "RIPng for IPv6", RFC 2080,
January 1997.
[RFC2328] Moy, J., "OSPF Version 2", STD 54, RFC 2328, April 1998.
[RFC2453] Malkin, G., "RIP Version 2", STD 56, RFC 2453, November
1998.
[RFC3830] Arkko, J., Carrara, E., Lindholm, F., Naslund, M., and K.
Norrman, "MIKEY: Multimedia Internet KEYing", RFC 3830,
August 2004.
[RFC4046] Baugher, M., Canetti, R., Dondeti, L., and F. Lindholm,
"Multicast Security (MSEC) Group Key Management
Architecture", RFC 4046, April 2005.
[RFC4593] Barbir, A., Murphy, S., and Y. Yang, "Generic Threats to
Routing Protocols", RFC 4593, October 2006.
[RFC4732] Handley, M., Rescorla, E., IAB, "Internet Denial-of-
Service Considerations", RFC 4732, December 2006.
[RFC4949] Shirey, R., "Internet Security Glossary, Version 2", RFC
4949, August 2007.
[RFC5055] Freeman, T., Housley, R., Malpani, A., Cooper, D., and W.
Polk, "Server-Based Certificate Validation Protocol
(SCVP)", RFC 5055, December 2007.
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[RFC5197] Fries, S. and D. Ignjatic, "On the Applicability of
Various Multimedia Internet KEYing (MIKEY) Modes and
Extensions", RFC 5197, June 2008.
[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.
[RFC5751] Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
Mail Extensions (S/MIME) Version 3.2 Message
Specification", RFC 5751, January 2010.
[RFC5826] Brandt, A., Buron, J., and G. Porcu, "Home Automation
Routing Requirements in Low-Power and Lossy Networks", RFC
5826, April 2010.
[RFC5867] Martocci, J., De Mil, P., Riou, N., and W. Vermeylen,
"Building Automation Routing Requirements in Low-Power and
Lossy Networks", RFC 5867, June 2010.
[RFC5996] Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
"Internet Key Exchange Protocol Version 2 (IKEv2)", RFC
5996, September 2010.
[RFC6192] Dugal, D., Pignataro, C., and R. Dunn, "Protecting the
Router Control Plane", RFC 6192, March 2011.
[Szcze2008]
Szczechowiak1, P., Oliveira, L., Scott, M., Collier, M.,
and R. Dahab, "NanoECC: testing the limits of elliptic
curve cryptography in sensor networks", pp. 324-328, 2008,
<http://www.ic.unicamp.br/~leob/publications/ewsn/
NanoECC.pdf>.
[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.
[Wander2005]
Wander, A., Gura, N., Eberle, H., Gupta, V., and S.
Shantz, "Energy analysis of public-key cryptography for
wireless sensor networ", in the Proceedings of the Third
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IEEE International Conference on Pervasive Computing and
Communications pp. 324-328, March 8-12 2005.
[Yourdon1979]
Yourdon, E. and L. Constantine, "Structured Design",
Yourdon Press, New York, Chapter 10, pp. 187-222, 1979.
Authors' Addresses
Tzeta Tsao
Cooper Power Systems
910 Clopper Rd. Suite 201S
Gaithersburg, Maryland 20878
USA
Email: tzeta.tsao@cooperindustries.com
Roger K. Alexander
Cooper Power Systems
910 Clopper Rd. Suite 201S
Gaithersburg, Maryland 20878
USA
Email: roger.alexander@cooperindustries.com
Mischa Dohler
CTTC
Parc Mediterrani de la Tecnologia, Av. Canal Olimpic S/N
Castelldefels, Barcelona 08860
Spain
Email: mischa.dohler@cttc.es
Vanesa Daza
Universitat Pompeu Fabra
P/ Circumval.lacio 8, Oficina 308
Barcelona 08003
Spain
Email: vanesa.daza@upf.edu
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Angel Lozano
Universitat Pompeu Fabra
P/ Circumval.lacio 8, Oficina 309
Barcelona 08003
Spain
Email: angel.lozano@upf.edu
Michael Richardson (ed)
Sandelman Software Works
470 Dawson Avenue
Ottawa, ON K1Z5V7
Canada
Email: mcr+ietf@sandelman.ca
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