6Lowpan Working Group S. Daniel Park
Internet-Draft Samsung Electronics
Expires: August 20, 2008 K. Kim
Ajou University
E. Seo
Samsung AIT
S. Chakrabarti
IP infusion
J. Laganier
DoCoMo Euro-Labs
February 2008
IPv6 over Low Power WPAN Security Analysis
draft-daniel-6lowpan-security-analysis-02.txt
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Copyright (C) The IETF Trust (2008).
Park, et al. [Page 1]
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Abstract
This document discusses possible threats and security options for
IPv6-over-IEEE802.15.4 networks. It is an informational document to
raise awareness of security issues in IPv6 lowPan networks.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5. Security Threats . . . . . . . . . . . . . . . . . . . . . . . 8
6. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 10
7. 6lowpan security analysis . . . . . . . . . . . . . . . . . . 11
7.1. IEEE 802.15.4 Security analysis . . . . . . . . . . . . . 11
7.2. IP Security analysis . . . . . . . . . . . . . . . . . . . 12
8. Key Management in 6lowpan . . . . . . . . . . . . . . . . . . 14
8.1. Existing Key management methods . . . . . . . . . . . . . 14
8.2. Issues with Key management in 6lowpan . . . . . . . . . . 15
9. Security consideration in bootstrapping a 6lowpan node . . . . 16
10. Possible scenarios using different levels of security . . . . 17
11. Security Considerations . . . . . . . . . . . . . . . . . . . 18
12. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
13. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 20
14. No I-D References . . . . . . . . . . . . . . . . . . . . . . 21
15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 22
15.1. Normative References . . . . . . . . . . . . . . . . . . . 22
15.2. Informative References . . . . . . . . . . . . . . . . . . 22
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 23
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1. Introduction
The principal object of the 6lowpan working group is to design IPv6
transmission over IEEE 802.15.4 [ieee802.15.4] networks.
IEEE 802.15.4 [ieee802.15.4] is designed to support variety of
applications in personal area networks; many of applications are
security sensitive.
Specifically, some of the IEEE 802.15.4 optional features actually
reduce security and implementation would be limited for their
extensions. The applications range from defense systems to building
monitoring, fire-safety, patient monitoring etc. If the network is
not secured, an intruder can inject incorrect messages to trigger
false situations. Thus link-layer security is quite necessary in
IEEE802.15.4 networks.
IEEE 802.15.4 is working on improving the link-layer security
specification. However, this document will focus on discussing
different security threats from the 6lowpan perspective and discuss
different options of applying existing security methods to overcome
those threats. The goal is to provide a trust model using both link-
layer and IP layer security packages, if possible.
Designing a new security protocol for 6lowpan network is out of scope
of this document. However, it may state desired security
requirements which can be fed to the appropriate IETF security
working group in order to suggest appropriate security protocols.
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2. Requirements
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
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3. Terminology
This document uses terminology specific to IPv6 and DHCPv6 as defined
in "Terminology" section of the DHCPv6 specification [RFC3315].
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4. Overview
As described in [RFC4919], unlike regular IP network 6lowpan has some
special characteristics such as small packet size, low bandwidth of
IEEE 802.15.4 standard [ieee802.15.4], low power, low cost, large
number of devices, etc. The security aspect, however, seems a bit
tradeoff in the 6lowpan since security is always a costly function.
This is particularly true to low rate WPAN. Obviously, adding
security makes the issue even more challenging. For instance, when
putting IPv6 on top of 6lowpan, it seems one could use IP security
and turn off the security of WPAN since the security architecture
defined by IEEE 802.15.4. But on the other hand, IP security is
relatively mature for services at IP or other upper layers.
It is naturally questionable whether the 6lowpan devices can support
IP Security (IPSec) as it is. This document explains some of
difficulties of adopting IPSec in the following sections. However,
Layer 2 security must be used for Layer-2 level operations such as
MAC sublayer association, beaconing, orphaning, etc.
Security Considerations paper[802.15.4-ACM] outlines that
IEEE802.15.4 link-layer provides access control, message integrity,
message confidentiality and replay-protection services. Yet the
document is not clear about key management methods, state of ACL
table in the event of power loss and support of group keying.
Network shared common key may be an answer for link-layer security in
this case, but that is vulnerable with replay attacks and with stolen
devices. However, in most common cases, network shared keying may be
the simple answer to the security at the link-layer for the power-
deprived, reduced function-devices, as it is easily configurable
among hundreds of devices.
IPSec is mandatory to run IPv6, but considering power constraints and
limited processing capability of the IEEE802.15.4 capable devices
IPSec may be compute intensive; IKE messaging will not work well in
low power networks as we want to reduce signaling in this network.
Thus 6lowpan may need to define its own keying methods that require
minimum overhead in packet-size and of course a number of signaling
messages. IP-layer security will provide authentication and
confidentiality between end-nodes and across multiple lowpan-links.
This document later discusses applicability of IP-layer security in
the case of 6lowpan network usage and applications. IP-layer
security may be useful only when two nodes want to send/receive all
messages securely. However, in most cases, the security may be
requested at the application layer as needed, while other messages
can flow in the network without security overhead.
The possible threats in this type of network are intrusion, sink-hole
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and replay attacks. A third party entity can inject bad routes in
the network, act as a default router attracting all the packets to
itself, or it can snoop packets and then launch replay attacks on the
6lowpan nodes. These attacks can cause harm especially when the
attacker is a high-power device, such as a laptop. It can easily
drain batteries of the 6lowpan devices by sending broadcast messages,
redirecting routes etc.
A possible solution to security issues in the 6lowpan network might
be application level security (for example, SSL) on top of link-layer
security. Link-layer security protects from intrusion in the link
and the application-level security protects from another user peeking
at the data and impersonation.
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5. Security Threats
Most of the attacks and threats against user and data security in
6lowpan are plausible and MAY be very destructible in effect, because
of its wireless radio access and connectivity to the Internet. The
security analysis of 6lowpan starts with the appreciation of various
threats posed at respective ISO OSI layers. In this section, we
classify and discuss the threats in layer-wise order.
6lowpan is highly susceptible to physical attacks. i.e., threats due
to physical node destruction relocation and masking. By the Physical
attacks, 6lowpan nodes can be condemned permanently, so the losses
are irreversible. Physical attack can extract cryptographic secrets
from the associated circuitry, modify programming in the sensors, and
the malicious node can take control over them. These compromises can
result into code modification inside the sensor node to change the
mission-oriented roles of full fledged networks, let alone sensors.
In 6lowpan environment, several types of DoS attacks can be triggered
in different layers. At the Physical Layer, the DoS attacks could be
tempering and jamming electromagnetic (EM) signals. It can be
executed by swarming the limited resources of 6lowpan devices by the
high resource devices very easily. At the Link Layer, it could be
collision and contention of deliberate stray frames. At the Network
Layer, it could be the an outburst of packets in the name of network
traffic during homing. At the Transport Layer, attacks could be
performed by half open and half close TCP segments. Because of its
internet connectivity, 6lowpan is highly vulnerable as those kinds of
attacks can exacerbate.
Since some 6lowpan nodes might need to work together to execute a
complete task, there is a burgeoning need to distribute subtasks and
ensure redundancy of information. Sybil Attacks MAY also be
triggered in such 6lowpan environments. In such a kind of attack, a
node can pretend to be more than one node, using the identities of
other sensors. Sybil attacks MAY be performed against the
distributed storage, routing mechanism, data aggregation, voting,
fair resource-allocation and misbehavior detection, etc. It is not
very easy to be aware of a Sybil attack in progress, but measuring
the usage of radio resources, the Sybil attacks MAY be detected,
though with very little probability.
In the Black Hole attack, a malicious node acts as a black hole to
attract all the traffic in the sensor network. In this attack, the
attacker listens to requests for routes then replies to the
requesting nodes that it contains the high quality or shortest path
to the base station. Once the malicious device is able to insert
itself between the communication nodes, it is able to do anything
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with the packets passing through it. In fact, this attack can affect
even the nodes those are spatially farther from the malicious node.
In the Wormhole attack, the attacker records the packets (or bits) at
one location in the network and tunnels those to another location.
Such attacks can be fatal to the working for the 6lowpan, since, this
sort of attack does not require compromising a sensor in the network;
rather it could be performed even at the initial phase when the
sensors start to discover the neighboring information.
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6. Assumptions
The [RFC4919] describes two security concerns as follows;
In Section 4.6 Security: Although IEEE 802.15.4 provides AES link
layer security, a complete end-to-end security is needed.
In Section 5 Goals: Security threats at different layers must be
clearly understood and documented. Bootstrapping of devices into a
secure network could also be considered given the location, limited
display, high density and ad hoc deployment of devices.
This document will meet the above considerations.
In addition, existing IP security technologies will be simplified to
be implemented on the 6lowpan small devices. 6lowpan security
architecture will shed off lots of fat from IP security technologies
whenever available.
IEEE 802.15.4 AES (Advanced Encryption Standard) will be used for
6lowpan security architecture in conjunction with IP security
whenever available.
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7. 6lowpan security analysis
In this section, both IEEE 802.15.4 MAC security and IP security are
tackled to search for a new 6lowpan trust models and available
solution spaces if feasible. The principal object of these analysis
is to improve 6lowpan security level as we use IP layer security
mechanism as possible regardless of 802.15.4 vulnerable MAC security.
802.15.4 MAC enhancement and amendment are not scope of this document
but IEEE 802 standard stuff.
7.1. IEEE 802.15.4 Security analysis
The MAC of IEEE 802.15.4 provides security services that are
controlled by the MAC PIB (PAN Information Base). For security
purpose, the MAC sublayer maintains an access control list (ACL) in
its MAC PIB. By specifying a security suite in the ACL for a
communication peer, a device can indicate what level security should
be used (i.e., none, access control, data encryption, frame
integrity, etc.) for communications with that peer. In addition, MAC
sublayer offers a secured mode and an unsecured mode.
A critical function of IEEE 802.15.4 MAC is frame security. Frame
security is actually a set of optional services that may be provided
by the MAC to the upper layers (applications). The standard strikes
a balance between the need for these services in many applications,
and the desire to minimize the burden of their implementation on
those applications that do not need them. As described in [802.15.4-
ACM], if an application does not set any security parameters, then
security is not enabled by default. The [ieee802.15.4] defines four
packet types: beacon packets, data packets, acknowledgements packets
and control packets for the media access control layer. It does not
support security for acknowledgement packets. But on the other hand,
other packet types can optionally support integrity protection and
confidentiality protection for the packet's data field.
Due to the variety of applications targeted by IEEE 802.15.4, the
processes of authentication and key exchange are not defined in the
standard. Devices without the key cannot decrypt the encryped
messages.
In addition, unsecured mode is suitable for some applications in
which implementation cost is important, and security is either not
required or obtained in other ways. An example of this is that all
6lowpan devices are assigned a default key by the administrator they
can exchange data encrypted with that key. This may work in some
situations, but this solution is not quite scalable. In this case,
802.15.4 node is very vulnerable.
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The security service enables the MAC to select the devices with which
it is willing to communicate. The device may decide to communicate
with some devices, and not others. To minimize complexity, the
access control service is performed on an individual device basis,
rather than on groups or collections of devices.
Unlike file transfer or voice communication applications common with
other protocols, IEEE 802.15.4 applications often transmit messages
that do not convey secret information.
7.2. IP Security analysis
IPsec (IP security protocol) can guarantee integrity and optionnaly
confidentiality of IP (v4 or v6) packets exchanged between two peers.
Basically, IPsec works well on non-low-power devices which are not
subject to severe constraints on host software size, processing and
transmission capacities. IPSec supports AH for authenticating the IP
header and ESP for authenticating and encrypting the payload. The
main issues of using IPSec are two-fold: (1) processing power and (2)
key management. Since these tiny 6lowpan devices do not process huge
number of data or communicate with many different nodes, it is not
well understood if complete implementation of SADB, policy-database
and dynamic key-management protocol are appropriate for these small
battery-powered devices.
Given constraints existing in 6lowpan environments, IPsec might not
be suitable as is to use in such environments. Especially, 6lowpan
node may not be able to operate all IPsec algorithms on its own
capability either FFD or RFD.
Bandwidth is a very scarce resource in 6lowpan environments. The
fact that IPsec additionally requires another header (AH or ESP) in
every packet, thus increasing per-packet header overhead, makes its
use problematic in 6lowpan environments.
IPsec requires two communicating peers to share a secret key that is
typically established dynamically with the IKE (Internet Key
Exchange) protocol. Thus, it has an additional packet overhead
incurred by IKE packets exchange.
If NDP (Neighbor Discovery Protocol) is applied to 6lowpan, SeND
(Secure Neighbor Discovery) should at least considered to provide
security in conjunction with neighbor discovery protocol. So far,
CGA (Cryptographically Generated Addresses) [RFC3972] and SeND
options [RFC3971] are newly designed by IETF and it works well over
existing IP networks. However, RSA based CGA and SeND options could
requires larger packet-size and processing time than ECC based keying
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algorithm. Therefore, it could be reasonable to use the Secure
Neighbor Discovery protocol if it is extended to support ECC for
6lowpan networks application.
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8. Key Management in 6lowpan
In order to provide security in 6lowpans, a robust encryption
mechanism MUST be in place. Only the non-tamperable keys can provide
an encryption infrastructure that is thorough enough to provide a
wide range of security services such as but not limited to
authentication, authorization, non-repudiation and prevention from
replay attacks. In this section, the important issue of key
management is discussed.
8.1. Existing Key management methods
The characteristics of sensors, communicating devices and resulting
sensor networks, such as limited resources at the node and network
level, lack of physical protection, unattended operation, and a close
interaction with the physical environment, all make it infeasible to
implement some of the most popular key exchange techniques in their
literal forms for 6lowpans. In this section, we visit the three
widely known schemes such as trusted-server scheme, pre-distribution
scheme and public key cryptography schemes in order to reach to a
pragmatic key management mechanism for 6lowpans.
The trusted-server scheme relies solely on the server for key
agreement between nodes, e.g., Kerberos. If the server is
compromised, the trust amongst sensor nodes is severed. Such a
scheme is not suitable for sensor networks because there is usually
no guarantee of communicating seamlessly with a trusted server at all
the times in sensor networks.
The key agreement scheme is key pre-distribution, where key
information is distributed among all sensor nodes prior to
deployment. If the network deployers were to know which nodes were
more likely to stay in the same neighborhood before deployment, keys
MAY be decided a priori. However, because of the randomness of the
deployment, knowing the set of neighbors deterministically might not
be feasible. Furthermore, the presence of intruder nodes right from
the network deployment and initiation time cannot be rejected
outright as implausible. Some schemes like network shared keying,
pair-wise keying, and group keying, have been defined as variants of
key distribution. On-site key management mechanisms, while
warranting the same level of security as key pre-distribution schemes
have an obvious edge to cope up with network dynamics.
This class of key management scheme depends on asymmetric
cryptography, such as public key certificates that are irreversible
singularly. This irreversibility comes at a price-often staked by
the limited computation and energy resources of sensor nodes.
However, these are the hardest cryptanalyze. Some of the most
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popular examples include, but are not limited to Diffie-Hellman key
agreement, RSA or ECC [RFC2631]. Recent works on ECC implementation
for low power devices has proven its feasibility for sensor networks.
It provides security with smaller key size that is comparable to
security provided by RSA or AES with much higher key size.
Network topologies for 6LowPan (i.e star and mesh) and presence of
FFD and RFD makes cluster based dynamic key management schemes the
most appropriate. These schemes use Master Keys; Network Keys and
Links keys which could be pre installed for first round and can be
distributed by key transport mechanism during later rounds. This
scheme provides ease in key distribution and key revocation [ZigBee].
8.2. Issues with Key management in 6lowpan
-In a 6lowpan, a malicious node MAY sit amongst other nodes at the
deployment phase-a problem of secure key assignment at bootstrap
time.
-A node is compromised during the operating time of 6lowpan-A key
revocation system MUST be employed.
-In a sleep-mode enabled 6lowpan, keys to sleeping nodes MUST be
deprived and reinstated after such nodes resume active state.
-In case the keys are compromised, a mechanism to diagnose security
violation MUST be invoked.
-It SHOULD allow and support dynamic addition of a new node.
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9. Security consideration in bootstrapping a 6lowpan node
This section should discuss how does a node configures itself
securely with a IPv6 router in the network. It involves assignment
of IPv6 prefix and the default IPv6 router in the 6lowpan. Further
details will be collaborated with 6lowpan commissioning/bootstrapping
works in near futhre according to the 6lowpan working group
rechartering.
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10. Possible scenarios using different levels of security
This section may suggest example scenarios with example solutions in
different cases (IPSec, SSL, other type of Solutions) although this
document does not recommend or specify any security solutions.
Further details will be collaborated with 6lowpan architecture works
in near futhre according to the 6lowpan working group re-chartering.
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11. Security Considerations
This document addresses only security issues around IPv6 over Low
Power WPAN.
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12. IANA Considerations
There is no IANA considerations.
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13. Acknowledgements
Thanks to Myungjong Lee at CUNY, USA, Rabia Iqbal, Mustafa Hasan and
Ali Hammad Akbar all at Ajou University for their valuable comments
to improve the document. Special thanks to Jung-Hyun Oh for his
valuable help on this document.
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14. No I-D References
All references shown in this section MUST be added into the
Informative References before publishing it officially.
[ieee802.15.4] IEEE Std., 802.15.4-2003, ISBN 0-7381-3677-5, May
2003.
[802.15.4-ACM] Sastry, N. and Wagner, D., Security Considerations for
IEEE 802.15.4 Networks, ACM WiSE'04, October 2004.
[ZigBee] Specification Version 1.0, December 2004.
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15. References
15.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3315] Droms, R., Bound, J., Volz, B., Lemon, T., Perkins, C.,
and M. Carney, "Dynamic Host Configuration Protocol for
IPv6 (DHCPv6)", RFC 3315, July 2003.
15.2. Informative References
[RFC2631] Rescorla, E., "Diffie-Hellman Key Agreement Method",
RFC 2631, June 1999.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC3972] Aura, T., "Cryptographically Generated Addresses (CGA)",
RFC 3972, March 2005.
[RFC4919] Kushalnagar, N., Montenegro, G., and C. Schumacher, "IPv6
over Low-Power Wireless Personal Area Networks (6LoWPANs):
Overview, Assumptions, Problem Statement, and Goals",
RFC 4919, August 2007.
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Authors' Addresses
Soohong Daniel Park
System Solution Laboratory, Samsung Electronics.
Email: soohong.park@samsung.com
Ki-Hyung Kim
Ajou University
Email: kkim86@ajou.ac.kr
Eunil Seo
Samsung AIT
Email: eunil.seo@samsung.com
Samita Chakrabarti
IP infusion
Email: samitac@ipinfusion.com
Julien Laganier
DoCoMo Euro-Labs
Email: lulien.ietf@laposte.net
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