Network Working Group H. Rafiee
INTERNET-DRAFT Ciber AG
Intended Status: Informational Track C. Meinel
Hasso Plattner Institute
Expires: August 8, 2014 Februar 8, 2014
Possible Attack on Cryptographically Generated Addresses (CGA)
<draft-rafiee-6man-cga-attack-01.txt>
Abstract
This document describes the new vulnerability with the use of
Cryptographically Generated Addresses.
Status of this Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on June 4, 2014.
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the Trust Legal Provisions and are provided without warranty as
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Sec value vulnerability . . . . . . . . . . . . . . . . . . . 3
2.1. Duplicate Address Detection Process . . . . . . . . . . . 4
2.2. Nodes communications . . . . . . . . . . . . . . . . . . 5
3. Security Considerations . . . . . . . . . . . . . . . . . . . 5
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
5. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5
7.1. Normative . . . . . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 7
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1. Introduction
Cryptographically Generated Addresses (CGA) [RFC3972] is one of the
important options of Secure Neighbor Discovery (SeND) [RFC3971] in
IPv6 networks. CGA provides the node with the proof of IP address
ownership by finding a binding between the public key and the node's
IP address. Therefore, It can protect the nodes from network layer IP
spoofing attack and prevent forging the identity (if it is only based
on the IP address). However, CGA, itself is vulnerable to some types
of attacks such as DoS, replay attack (The use of timestamp would
mitigate this attack), etc [3]. The goal of this document is not to
focus on the well-known attacks but the new CGA vulnerabilities.
2. Sec value vulnerability
CGA values are the fingerprint of public key. They are generated by
executing a hash function on public key and some other parameters.
Since the default algorithm for generating this hash is SHA-1, the
attacker node only needs to do brute force attacks against 59 bits.
CGA algorithm uses sec value (a value between 0 to 7) to increase the
brute force search space from 59 bits to maximum 171 bits (59+sec*16)
and as a result complicates the brute force attacks to break CGA.
Nevertheless, in practice, only sec value 0 and 1 can be used because
it takes hours to years to generate CGA sec value higher than 1 [2].
Unfortunately, in practice, it does not matter what sec value the
victim node chooses and the use of sec value only complicates the IP
address generation process for the victim node. This is because the
attacker will only use sec value 0 and SHA1 algorithm.
The reason are as follow:
- No comparison of source address and target address
Based on the Neighbor Discovery Protocol (NDP) specification on
section 7 RFC 4861 [RFC4861, RFC4862], there is nothing about to
compare the source IP address with the target address. In SeND
specification [RFC3971], there are rules for the sender node.
However, the verifier node never checks those rules. This is why the
attacker can ignore them. So, the attacker can create the SeND
message by using his own CGA address that differs only in sec value.
The attacker selects the victim node's source address as his own
target address and sends this message.
- The CGA verifier node ignores 3 bits sec value in source address
and 2 bits u and g
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Based on NDP specification, the verifier node checks to see whether
or not the target address is the same as its own IP address. If it is
the same and the node supports CGA, then it starts CGA verification.
Based on step 4 section 5 RFC 3972, the CGA node compares the source
address (IID section) of the sender node to his own IID. The verifier
node ignores 3 bits sec value. So, the attacker can set the target
address to the real CGA address of the victim node disregard its sec
value and set the source address to his own CGA value that is only
different in the 3 leftmost bits. Since the verification is
successful, the attacker can spoof the IP address of CGA node.
- Either conflict on the network or the CGA node waive his rights on
the IP address
The attacker node can persist on his own IP address after a
successful verification by CGA node and either force CGA node to
generate a new IP address and again the attacker repeats this process
or there will be duplicate addresses on the network which cause many
services in the victim network stop working. This is because all the
nodes verify this attacker node the same way as the legitimate CGA
node processed the verification. From their aspects, these two nodes
are the same.
The mentioned flaw occurs during verification processes in all
verifier nodes. The node needs to verify other nodes in two different
conditions -- during DAD process and during checking the neighbors'
reachability in cache. This means that the CGA security is only the
security of CGA sec value 0 that is 2^59 bits.
- The lower limit for key size is 384 bits
The attacker does not need to worry about attack on public key and he
can choose the lowest size public key so that he can better play with
the RSA values and easier and faster generates the similar hash of
the CGA node.
- Modifier can be zero
The attacker does not need to generate a really good random value.
Since for him it is only important to match the hash value. This is
especially true for the scenario where the attacker needs to do brute
force attacks against all 64 bits and sec value is not ignored.
In the following subsections, some of these attacks are explained in
more detail.
2.1. Duplicate Address Detection Process
When a node generates his IP address, it process the DAD in order to
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avoid collision on the network. The attacker might be able to
generate the CGA value the same of the legitimate CGA node and claim
the ownership of that IP address. The CGA nodes only tries 3 times
and then it gives up.
2.2. Nodes communications
When two nodes want to start communication, they try to find the IP
address of eachother by sending multicast NS/NA messages. If the
attacker can generate the CGA of one of these nodes, he can spoof the
identity of them. This is what against the CGA goal.
3. Security Considerations
-
4. IANA Considerations
-
5. Appendix
- CGA multicore attack
This is where you can find CGA attacks (multicore). More attacks will
uploaded in the following link:
http://www.hpi.uni-potsdam.de/meinel/security_tech/ipv6_security/ipv6ssl.html
6. Acknowledgements
The author would like to acknowledge Fabian Braeunlein, one of a
bachelor student at Hasso Plattner Institute who assists us, during
this busy moments, for writing the attacking codes.
7. References
7.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to
Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.
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[RFC3972] Aura, T., "Cryptographically Generated Addresses
(CGA)," RFC 3972, March 2005.
[RFC3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander,
"SEcure Neighbor Discovery (SEND)", RFC 3971, March 2005.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., Soliman,
H., "Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
[RFC4862] Thomson, S., Narten, T., Jinmei, T., "IPv6
Stateless Address Autoconfiguration", RFC 4862, September
2007.
[1] AlSa'deh, A., Rafiee, H., Meinel, C., "Cryptographically
Generated Addresses (CGAs): Possible Attacks and Proposed
Mitigation Approaches," in proceedings of 12th IEEE International
Conference on Computer and Information Technology (IEEE CIT'12),
pp.332-339, 2012.
[2] Bos, J., Oezen, O., Hubaux, J., "Analysis and Optimization of
Cryptographically Generated Addresses", In Proceedings of the
12th International Conference on Information Security (2009),
ACM, pp. 17 ? 32.
[ugbits] Carpenter, B., Jiang, S., "Significance of IPv6
Interface Identifiers",
http://tools.ietf.org/html/draft-ietf-6man-ug, November 2013
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Authors' Addresses
Hosnieh Rafiee
Ciber AG
KoelnTurm
Im Mediapark 8
http://www.ciber.com
Phone: +49 (0221) 272 67- 122
Email: ietf@rozanak.com
Christoph Meinel
Hasso-Plattner-Institute
Prof.-Dr.-Helmert-Str. 2-3
Potsdam, Germany
Email: meinel@hpi.uni-potsdam.de
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