Network Working Group S. Daniel Park
Internet-Draft SAMSUNG Electronics
Expires: December 24, 2006 K. Kim
Ajou University
E. Seo
Samsung AIT
S. Chakrabarti
June 22, 2006
IPv6 over Low Power WPAN Security Analysis
draft-daniel-6lowpan-security-analysis-01.txt
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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.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
5. Security Threats . . . . . . . . . . . . . . . . . . . . . . . 5
6. Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . 5
7. 6lowpan security analysis . . . . . . . . . . . . . . . . . . 5
7.1. IEEE 802.15.4 Security analysis . . . . . . . . . . . . . 6
7.2. IP Security analysis . . . . . . . . . . . . . . . . . . . 7
8. Key Management in 6lowpan . . . . . . . . . . . . . . . . . . 7
8.1. Existing Key management methods . . . . . . . . . . . . . 8
8.2. Issues with Key management in 6lowpan . . . . . . . . . . 8
9. Security consideration in bootstrapping a 6lowpan node . . . . 8
10. Possible scenarios using different levels of security . . . . 8
11. 6lowpan trust models . . . . . . . . . . . . . . . . . . . . . 8
12. Security Considerations . . . . . . . . . . . . . . . . . . . 8
13. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
15. No I-D References . . . . . . . . . . . . . . . . . . . . . . 9
16. References . . . . . . . . . . . . . . . . . . . . . . . . . . 9
16.1. Normative References . . . . . . . . . . . . . . . . . . . 9
16.2. Informative References . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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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.
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].
3. Terminology
This document uses terminology specific to IPv6 and DHCPv6 as defined
in "Terminology" section of the DHCPv6 specification [RFC3315].
4. Overview
As described in [I-D.ietf-6lowpan-problem], 6lowpan has some of the
characteristics against existing IP networks such as small packet
size, low bandwidth of IEEE 802.15.4 standard [ieee802.15.4], low
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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.
But of course, it is a question whether those 6lowpan devices can
support IP security as it is. for low layer services, for example MAC
sublayer association, beaconing, orphanning, etc. WPAN security must
be used since IP security is not supposed to take care of lower
layers.
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
LowPower 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 ofcourse 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. It 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
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
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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.
Further study in the next version.
5. Security Threats
TBD
6. Assumptions
The [I-D.ietf-6lowpan-problem] 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 try to 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.
Further study in the next version.
7. 6lowpan security analysis
In this section, both IEEE 802.15.4 MAC security and IP security are
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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. In this case, 802.15.4 node is
very vulnerable.
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.
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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.
Further study in the next version.
7.2. IP Security analysis
IPsec (IP security protocol) provides per-packet authenticity and
confidentiality guarantees between peers communicate using IPsec. It
is available for both IPv4 and IPv6.
Basically, IPsec targets to general IP nodes operated over ethernet.
It means each node has some of fluent stack size, bandwidth and non-
low cost limitations like 6lowpan.
Given the IPsec background, it is at least not suitable for 6lowpan
nodes. Especially, 6lowpan node may not be able to operate all IPsec
algorithms on its own capability either FFD or RFD.
Bandwidth is very sensitive element in the 6lowpan, but IPsec
generates some of redundant packets such as AH/ESP header.
IPsec needs shared secret key between nodes called IKE (Internet Key
Exchange), and it will make the key exchange in secrecy possible. It
can, however cause some of redundant packets over the 6lowpan
networks.
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, CGA seems very complex to be applied
to 6lowpan networks. Furthermore, SeND options requires huge
additional options (i.e., CGA option, RSA Signature option, Timestamp
and Nonce option and etc.) which increase the packet size
accordingly. Thus it is doubtful if Secure Neighbor Discovery
protocol could be directly applicable to 6lowpan networks without any
optimization.
Further study in the next version.
8. Key Management in 6lowpan
TBD
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8.1. Existing Key management methods
TBD
8.2. Issues with Key management in 6lowpan
TBD
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.
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.
11. 6lowpan trust models
To meet the security requirement of 6lowpan, a new trust models
including new IPsec hashing algorithms, new key exchange schemes,
etc.
6lowpan bootstraping should be at least considered as one of 6lowpan
trust models.
Since this document does not provide any particular solution, further
specific mentions should be aligned with WG consensus.
12. Security Considerations
This document addresses only security issues around IPv6 over Low
Power WPAN.
13. IANA Considerations
There is no IANA considerations.
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14. Acknowledgements
Thanks to Myungjong Lee of CUNY for his valuable comments on this
document.
15. 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.
16. References
16.1. 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.
16.2. Informative References
[I-D.ietf-6lowpan-problem]
Kushalnagar, N. and G. Montenegro, "6LoWPAN: Overview,
Assumptions, Problem Statement and Goals",
draft-ietf-6lowpan-problem-02 (work in progress),
February 2006.
[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.
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Authors' Addresses
Soohong Daniel Park
Mobile Convergence 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
Email: samitac2@gmail.com
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