draft-ietf-csi-hash-threat-04.txt   draft-ietf-csi-hash-threat-05.txt 
Network Working Group A. Kukec Network Working Group A. Kukec
Internet-Draft University of Zagreb Internet-Draft University of Zagreb
Intended status: Informational S. Krishnan Intended status: Informational S. Krishnan
Expires: April 19, 2010 Ericsson Expires: May 13, 2010 Ericsson
S. Jiang S. Jiang
Huawei Technologies Co., Ltd Huawei Technologies Co., Ltd
October 16, 2009 November 9, 2009
SeND Hash Threat Analysis SeND Hash Threat Analysis
draft-ietf-csi-hash-threat-04 draft-ietf-csi-hash-threat-05
Abstract
This document analysis the use of hashes in SeND, possible threats
and the impact of recent attacks on hash functions used by SeND.
Current SeND specification [rfc3971] uses the SHA-1 [sha-1] hash
algorithm and PKIX certificates [rfc5280] and does not provide
support for the hash algorithm agility. The purpose of the document
is to provide analysis of possible hash threats and to decide how to
encode the hash agility support in SeND.
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
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Copyright Notice Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights publication of this document. Please review these documents
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Abstract include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
This document analysis the use of hashes in SeND, possible threats described in the BSD License.
and the impact of recent attacks on hash functions used by SeND.
Current SeND specification [rfc3971] uses the SHA-1 [sha-1] hash
algorithm and PKIX certificates [rfc5280] and does not provide
support for the hash algorithm agility. The purpose of the document
is to provide analysis of possible hash threats and to decide how to
encode the hash agility support in SeND.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4 2. Impact of collision attacks on SeND . . . . . . . . . . . . . 4
3. Impact of collision attacks on SeND . . . . . . . . . . . . . 5 2.1. Attacks against CGAs in stateless autoconfiguration . . . 4
3.1. Attacks against CGAs in stateless autoconfiguration . . . 5 2.2. Attacks against PKIX certificates in ADD process . . . . . 5
3.2. Attacks against PKIX certificates in ADD process . . . . . 6 2.3. Attacks against the Digital Signature in the RSA
3.3. Attacks against the Digital Signature in the RSA Signature option . . . . . . . . . . . . . . . . . . . . . 6
Signature option . . . . . . . . . . . . . . . . . . . . . 7 2.4. Attacks against the Key Hash field in the RSA
3.4. Attacks against the Key Hash field in the RSA Signature option . . . . . . . . . . . . . . . . . . . . . 6
Signature option . . . . . . . . . . . . . . . . . . . . . 7 3. Support for the hash agility in SeND . . . . . . . . . . . . . 7
4. Support for the hash agility in SeND . . . . . . . . . . . . . 8 3.1. The negotiation approach for the SEND hash agility . . . . 7
4.1. The negotiation approach for the SEND hash agility . . . . 8 4. Security Considerations . . . . . . . . . . . . . . . . . . . 9
5. Security Considerations . . . . . . . . . . . . . . . . . . . 10 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.1. Normative References . . . . . . . . . . . . . . . . . . . 11
7.1. Normative References . . . . . . . . . . . . . . . . . . . 12 6.2. Informative References . . . . . . . . . . . . . . . . . . 11
7.2. Informative References . . . . . . . . . . . . . . . . . . 12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
1. Introduction 1. Introduction
SEND [rfc3971] uses the SHA-1 hash algorithm to generate the contents SEND [rfc3971] uses the SHA-1 hash algorithm to generate the contents
of the Key Hash field and the Digital Signature field of the RSA of the Key Hash field and the Digital Signature field of the RSA
Signature option. It also uses a hash algorithm (SHA-1, MD5, etc.) Signature option. It also uses a hash algorithm (SHA-1, MD5, etc.)
in the PKIX certificates [rfc5280] used for the router authorization in the PKIX certificates [rfc5280] used for the router authorization
in the ADD process. Recently there have been demonstrated attacks in the ADD process. Recently there have been demonstrated attacks
against the collision free property of such hash functions against the collision free property of such hash functions
[sha1-coll], and attacks against the PKIX X.509 certificates that use [sha1-coll], and attacks against the PKIX X.509 certificates that use
the MD5 hash algorithm [x509-coll] This document analyzes the effects the MD5 hash algorithm [x509-coll] This document analyzes the effects
of those attacks and other possible hash attacks on the SEND of those attacks and other possible hash attacks on the SEND
protocol. The document proposes changes to make it resistant to such protocol. The document proposes changes to make it resistant to such
attacks. attacks.
2. Terminology 2. Impact of collision attacks on SeND
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 RFC 2119 [rfc2119].
3. Impact of collision attacks on SeND
Due to the hash attacks demonstrated on the aforesaid hash algorithms Due to the hash attacks demonstrated on the aforesaid hash algorithms
a study was performed to assess the threat of these attacks on the a study was performed to assess the threat of these attacks on the
cryptographic hash usage in internet protocols [rfc4270]. This cryptographic hash usage in internet protocols [rfc4270]. This
document analyzes the hash usage in SEND following the approach document analyzes the hash usage in SEND following the approach
recommended by [rfc4270] and [new-hashes]. recommended by [rfc4270] and [new-hashes].
The basic cryptographic properties of a hash function are that it is The basic cryptographic properties of a hash function are that it is
both one-way and collision free. There are two attacks against the both one-way and collision free. There are two attacks against the
one-way property, the first-preimage attack and the second-preimage one-way property, the first-preimage attack and the second-preimage
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operations. However, attacks against the one-way property are not operations. However, attacks against the one-way property are not
feasible yet [rfc4270]. Up to date, all demonstrated attacks are feasible yet [rfc4270]. Up to date, all demonstrated attacks are
attacks against a collision-free property, in which an attacker attacks against a collision-free property, in which an attacker
produces two different messages m and m' such that hash(m)=hash(m'). produces two different messages m and m' such that hash(m)=hash(m').
The rest of the document deals with the collision attacks. The rest of the document deals with the collision attacks.
We will analyze the impact of hash attacks on SeND case by case in We will analyze the impact of hash attacks on SeND case by case in
this section. Through our analysis, we also discuss whether we this section. Through our analysis, we also discuss whether we
should support the hash agility in SeND. should support the hash agility in SeND.
3.1. Attacks against CGAs in stateless autoconfiguration 2.1. Attacks against CGAs in stateless autoconfiguration
Hash functions are used in the stateless autoconfiguration process Hash functions are used in the stateless autoconfiguration process
that is based on CGAs. Impacts of collision attacks on current uses that is based on CGAs. Impacts of collision attacks on current uses
of CGAs are analyzed in the update of the CGA specification of CGAs are analyzed in the update of the CGA specification
[rfc4982], which also enables CGAs to support the hash agility. CGAs [rfc4982], which also enables CGAs to support the hash agility. CGAs
provide the proof-of-ownership of the private key corresponding to provide the proof-of-ownership of the private key corresponding to
the public key used to generate the CGA. CGAs do not deal with the the public key used to generate the CGA. CGAs do not deal with the
non-repudiation feature, while collision attacks are mainly about non-repudiation feature, while collision attacks are mainly about
affecting the non-repudiation feature, i.e. in the collision attack affecting the non-repudiation feature, i.e. in the collision attack
against the CGA both of the CGA Parameters sets are choosen by an against the CGA both of the CGA Parameters sets are choosen by an
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Therefore, as [rfc4982] points out CGA based protocols, including Therefore, as [rfc4982] points out CGA based protocols, including
SeND, are not affected by the recent collision attacks. Regarding SeND, are not affected by the recent collision attacks. Regarding
the pre-image attacks, if pre-image attacks were feasible, an the pre-image attacks, if pre-image attacks were feasible, an
attacker would manage to find the new CGA Parameters based on the attacker would manage to find the new CGA Parameters based on the
associated, victim's CGA, and produce the Key Hash field and the associated, victim's CGA, and produce the Key Hash field and the
Digital Signature field afterwards using the new public key. Since Digital Signature field afterwards using the new public key. Since
the strength of all hashes in SEND depends on the strength of the the strength of all hashes in SEND depends on the strength of the
CGA, the pre-image attack is potentially dangerous, but it is not yet CGA, the pre-image attack is potentially dangerous, but it is not yet
feasible. feasible.
3.2. Attacks against PKIX certificates in ADD process 2.2. Attacks against PKIX certificates in ADD process
The second use of hash functions is for the router authorization in The second use of hash functions is for the router authorization in
the ADD process. Router sends to a host a certification path, which the ADD process. Router sends to a host a certification path, which
is a path between a router and the hosts's trust anchor, consisting is a path between a router and the hosts's trust anchor, consisting
of PKIX certificates. Researchers demonstrated attacks against PKIX of PKIX certificates. Researchers demonstrated attacks against PKIX
certificates with MD5 signature, in 2005 [new-hashes] and in 2007 certificates with MD5 signature, in 2005 [new-hashes] and in 2007
[x509-coll]. In 2005 were constructed the original and the false [x509-coll]. In 2005 were constructed the original and the false
certificate that had the same identity data and the same digital certificate that had the same identity data and the same digital
signature, but different public keys [new-hashes]. The problem for signature, but different public keys [new-hashes]. The problem for
the attacker is that two certificates with the same identity are not the attacker is that two certificates with the same identity are not
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only with certificates, attacks against certificates are even more only with certificates, attacks against certificates are even more
dangerous. Generally, the most dangerous are attacks against middle- dangerous. Generally, the most dangerous are attacks against middle-
certificates in the certification path, where for the cost of the one certificates in the certification path, where for the cost of the one
false certificate, an attacker launches an attack on multiple false certificate, an attacker launches an attack on multiple
routers. Regarding the attacks against certificates in SEND, the routers. Regarding the attacks against certificates in SEND, the
only attack that SEND is not suspectable to, is an attack against the only attack that SEND is not suspectable to, is an attack against the
Trust Anchor's certificate because it is not exchanged in SeND Trust Anchor's certificate because it is not exchanged in SeND
messages, i.e. it is not the part of the certification path in the messages, i.e. it is not the part of the certification path in the
ADD process. ADD process.
3.3. Attacks against the Digital Signature in the RSA Signature option 2.3. Attacks against the Digital Signature in the RSA Signature option
The computation of the Digital Signature field is described in The computation of the Digital Signature field is described in
[rfc3971]. The digital signature in the RSA Signature option is [rfc3971]. The digital signature in the RSA Signature option is
produced as the SHA-1 hash over the IPv6 addresses, the ICMPv6 produced as the SHA-1 hash over the IPv6 addresses, the ICMPv6
header, the ND message and other fields, e.g. the Message Type Tag header, the ND message and other fields, e.g. the Message Type Tag
and ND options [rfc3971], that is signed with the sender's private and ND options [rfc3971], that is signed with the sender's private
key. The sender's private key corresponds to the public key in the key. The sender's private key corresponds to the public key in the
CGA parameters structure. It is usually authorized through CGAs. CGA parameters structure. It is usually authorized through CGAs.
Possible attack on such explicit digital signature is a typical non- Possible attack on such explicit digital signature is a typical non-
repudiation attack, i.e. the Digital Signature field is vulnerable to repudiation attack, i.e. the Digital Signature field is vulnerable to
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in the beginning of the paragraph, he could underlay the false in the beginning of the paragraph, he could underlay the false
message. The fields that make sense to be changed are ND fields, as message. The fields that make sense to be changed are ND fields, as
opposite to the ICMPv6 fields which would be easy to reveal. opposite to the ICMPv6 fields which would be easy to reveal.
However, as denoted in [rfc4270], the structure of at least one of However, as denoted in [rfc4270], the structure of at least one of
two messages (m, m') in a collision attack is strictly predefined. two messages (m, m') in a collision attack is strictly predefined.
The previous requirement complicates the collision attack, but we The previous requirement complicates the collision attack, but we
have to take into account that a variant of SHA-1 was already have to take into account that a variant of SHA-1 was already
affected by recent collision attacks and we have to prepare for affected by recent collision attacks and we have to prepare for
future improved attacks. future improved attacks.
3.4. Attacks against the Key Hash field in the RSA Signature option 2.4. Attacks against the Key Hash field in the RSA Signature option
The Key Hash field is a SHA-1 hash of the public key from the CGA The Key Hash field is a SHA-1 hash of the public key from the CGA
Parameters structure in the CGA option. The pre-image attack against Parameters structure in the CGA option. The pre-image attack against
the Key Hash field is potentially dangerous, as in the case of all the Key Hash field is potentially dangerous, as in the case of all
other hashes in SEND, because the Key Hash field contains a non other hashes in SEND, because the Key Hash field contains a non
human-readable data. However the Key Hash field is not suspectable human-readable data. However the Key Hash field is not suspectable
to the collision attack, since in the collision attack an attacker to the collision attack, since in the collision attack an attacker
itself chooses both keys, k and k', where hash(k) = hash(k'). The itself chooses both keys, k and k', where hash(k) = hash(k'). The
reason for the former is that the associated public key is already reason for the former is that the associated public key is already
authorized through the use of CGAs, and possibly the certification authorized through the use of CGAs, and possibly the certification
path in the ADD process. path in the ADD process.
4. Support for the hash agility in SeND 3. Support for the hash agility in SeND
While all of analyzed hash functions in SeND are theoretically While all of analyzed hash functions in SeND are theoretically
affected by hash attacks, these attacks indicate the possibility of affected by hash attacks, these attacks indicate the possibility of
future real-world attacks. In order to increase the future security future real-world attacks. In order to increase the future security
of SeND, we suggest the support for the hash and algorithm agility in of SeND, the following possible approaches can be used.
SeND.
o The most effective and secure would be to bind the hash function o The most effective and secure would be to bind the hash function
option with something that can not be changed at all, like option with something that can not be changed at all, like
[rfc4982] does for CGA - encoding the hash function information [rfc4982] does for CGA - encoding the hash function information
into addresses. But, there is no possibilty to do that in SeND. into addresses. But, there is no possibilty to do that in SeND.
We could decide to use by default the same hash function in SeND We could decide to use by default the same hash function in SeND
as in CGA. The security of all hashes in SeND depends on CGA, ie. as in CGA. The security of all hashes in SeND depends on CGA, ie.
if an attacker could break CGA, all other hashes are automatically if an attacker could break CGA, all other hashes are automatically
broken. From the security point of view, at the moment, this broken. From the security point of view, at the moment, this
solution is more reasonable then defining different hash algorithm solution is more reasonable then defining different hash algorithm
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o The third possible solution is to encode the algorithm in the CGA. o The third possible solution is to encode the algorithm in the CGA.
However, this will reduce the strength of the CGAs and make them However, this will reduce the strength of the CGAs and make them
vulnerable to brute force attacks. vulnerable to brute force attacks.
o One of the possible solutions is also the hybrid solution, i.e. to o One of the possible solutions is also the hybrid solution, i.e. to
require the hash algorithm to be the same as CGA, if CGA option is require the hash algorithm to be the same as CGA, if CGA option is
present, and to use the Hash agility option if the CGA option is present, and to use the Hash agility option if the CGA option is
not present. not present.
4.1. The negotiation approach for the SEND hash agility 3.1. The negotiation approach for the SEND hash agility
None of the previous solutions supports the negotiation of the hash None of the previous solutions supports the negotiation of the hash
function. We suggest the negotiation approach for the SEND hash function. Another possibility is to use a negotiation approach for
agility based on the Supported Signature Algorithm option described the SEND hash agility such as the one based on the Supported
in [sig-agility]. Based on the processing rules described in Signature Algorithm option described in [sig-agility]. Based on the
[sig-agility] nodes find the intersection between the sender's and processing rules described in [sig-agility] nodes find the
the receiver's supported signature algorithms set, as well as the intersection between the sender's and the receiver's supported
preferred signature algorithm. When producing and validating hashes signature algorithms set, as well as the preferred signature
in SEND, nodes MUST observe the following rules: algorithm. When producing and validating hashes in SEND, nodes must
observe the following rules:
o In the ADD process, if any of the certificates in the o In the ADD process, if any of the certificates in the
certification path uses the signature algorithm which is not one certification path uses the signature algorithm which is not one
of the signature algorithms negotiated in the signature agility of the signature algorithms negotiated in the signature agility
process through the use of the Supported Signature Algorithms process through the use of the Supported Signature Algorithms
option, nodes MUST reject the Router Authorization certificate. option, nodes must reject the Router Authorization certificate.
o In order to produce the Digital Signature field, nodes MUST use o In order to produce the Digital Signature field, nodes must use
the signature algorithm negotiated in the signature agility the signature algorithm negotiated in the signature agility
process through the use of the Supported Signature Algorithms process through the use of the Supported Signature Algorithms
option. option.
o In order to produce the Key Hash field, nodes MUST use the hash o In order to produce the Key Hash field, nodes must use the hash
algorithm defined associated to the signature algorithm negotiated algorithm defined associated to the signature algorithm negotiated
in the signature agility process through the use of the Supported in the signature agility process through the use of the Supported
Signature Algorithms option. Signature Algorithms option.
5. Security Considerations 4. Security Considerations
This document analyzes the impact of hash attacks in SeND and offeres This document analyzes the impact of hash attacks in SeND and offeres
a higher security level for SeND by providing solution for the hash a higher security level for SeND by providing solution for the hash
agility support. agility support.
The negotiation approach for the hash agility in SeND based on the The negotiation approach for the hash agility in SeND based on the
Supported Signature Algorithms option is vulnerable to bidding-down Supported Signature Algorithms option is vulnerable to bidding-down
attacks, which is usual in the case of any negotiation approach. attacks, which is usual in the case of any negotiation approach.
This issue can be mitigated with the appropriate local policies. This issue can be mitigated with the appropriate local policies.
6. IANA Considerations 5. IANA Considerations
There have been no IANA considerations so far in this document. There have been no IANA considerations so far in this document.
7. References 6. References
7.1. Normative References
[rfc2119] Bradner, S., "Key words for use in RFCs to Indicate 6.1. Normative References
Requirement Levels", RFC 2119, March 1997.
[rfc3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure [rfc3971] Arkko, J., Kempf, J., Zill, B., and P. Nikander, "SEcure
Neighbor Discovery (SEND)", RFC 3971, March 2005. Neighbor Discovery (SEND)", RFC 3971, March 2005.
[rfc4270] Hoffman, P. and B. Schneier, "Attacks on Cryptographic [rfc4270] Hoffman, P. and B. Schneier, "Attacks on Cryptographic
Hashed in Internet Protocols", RFC 4270, November 2005. Hashed in Internet Protocols", RFC 4270, November 2005.
[rfc4982] Bagnulo, M. and J. Arrko, "Support for Multiple Hash [rfc4982] Bagnulo, M. and J. Arrko, "Support for Multiple Hash
Algorithms in Cryptographically Generated Addresses Algorithms in Cryptographically Generated Addresses
(CGAs)", RFC 4982, July 2007. (CGAs)", RFC 4982, July 2007.
[rfc5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S., [rfc5280] Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
Housley, R., and W. Polk, "Internet X.509 Public Key Housley, R., and W. Polk, "Internet X.509 Public Key
Infrastructure Certificate and Certificate Revocation List Infrastructure Certificate and Certificate Revocation List
(CRL) Profile", RFC rfc5280, May 2008. (CRL) Profile", RFC rfc5280, May 2008.
7.2. Informative References 6.2. Informative References
[new-hashes] [new-hashes]
Bellovin, S. and E. Rescorla, "Deploying a New Hash Bellovin, S. and E. Rescorla, "Deploying a New Hash
Algorithm", November 2005. Algorithm", November 2005.
[sha-1] NIST, FIBS PUB 180-1, "Secure Hash Standard", April 1995. [sha-1] NIST, FIBS PUB 180-1, "Secure Hash Standard", April 1995.
[sha1-coll] [sha1-coll]
Wang, X., Yin, L., and H. Yu, "Finding Collisions in the Wang, X., Yin, L., and H. Yu, "Finding Collisions in the
Full SHA-1. CRYPTO 2005: 17-36", 2005. Full SHA-1. CRYPTO 2005: 17-36", 2005.
[sig-agility] [sig-agility]
Cheneau, T. and M. Maknavicius, "Signature Algorithm Cheneau, T., Maknavicius, M., Shen, S., and M. Vanderveen,
Agility in the Secure Neighbor Discovery (SEND) Protocol", "Signature Algorithm Agility in the Secure Neighbor
draft-cheneau-send-sig-agility-00 (work in progress), Discovery (SEND) Protocol",
February 2009. draft-cheneau-csi-send-sig-agility-00 (work in progress),
October 2009.
[x509-coll] [x509-coll]
Stevens, M., Lenstra, A., and B. Weger, "Chosen-Prefix Stevens, M., Lenstra, A., and B. Weger, "Chosen-Prefix
Collisions for MD5 and Colliding X.509 Certificates for Collisions for MD5 and Colliding X.509 Certificates for
Different Identitites. EUROCRYPT 2007: 1-22", 2005. Different Identitites. EUROCRYPT 2007: 1-22", 2005.
Authors' Addresses Authors' Addresses
Ana Kukec Ana Kukec
University of Zagreb University of Zagreb
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