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Versions: (draft-kukec-csi-hash-threat) 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 6273

Network Working Group                                           A. Kukec
Internet-Draft                                      University of Zagreb
Intended status: Informational                               S. Krishnan
Expires: January 12, 2011                                       Ericsson
                                                                S. Jiang
                                            Huawei Technologies Co., Ltd
                                                           July 11, 2010


                       SEND Hash Threat Analysis
                     draft-ietf-csi-hash-threat-10

Abstract

   This document analyzes the use of hashes in Secure Neighbor Discovery
   (SEND), the possible threats to these hashes and the impact of recent
   attacks on hash functions used by SEND.  The SEND specification
   [RFC3971] currently uses the SHA-1 [SHA1] hash algorithm and PKIX
   certificates [RFC5280] and does not provide support for hash
   algorithm agility.  This document provides an analysis of possible
   threats to the hash algorithms used in SEND.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
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   This Internet-Draft will expire on January 12, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents



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   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . . 3
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . . . 3
   3.  Impact of collision attacks on SEND . . . . . . . . . . . . . . 3
     3.1.  Attacks against CGAs used in SEND . . . . . . . . . . . . . 3
     3.2.  Attacks against PKIX certificates in Authorization
           Delegation Discovery process  . . . . . . . . . . . . . . . 4
     3.3.  Attacks against the Digital Signature in the SEND RSA
           Signature option  . . . . . . . . . . . . . . . . . . . . . 4
     3.4.  Attacks against the Key Hash field of the SEND RSA
           Signature option  . . . . . . . . . . . . . . . . . . . . . 4
   4.  Conclusion  . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     7.1.  Normative References  . . . . . . . . . . . . . . . . . . . 5
     7.2.  Informative References  . . . . . . . . . . . . . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 6

























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1.  Introduction

   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
   Signature option.  It also indirectly uses a hash algorithm (SHA-1,
   MD5, etc.) in the PKIX certificates [RFC5280] used for router
   authorization in the Authorization Delegation Discovery(ADD) process.
   Recently there have been demonstrated attacks against the collision
   free property of such hash functions [SHA1-COLL], and attacks on the
   PKIX X.509 certificates that use the MD5 hash algorithm [X509-COLL].
   The document analyzes the impacts of these attacks on SEND and it
   recommends mechanisms to make SEND resistant to such attacks.


2.  Terminology

   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

   [RFC4270] performed a study to assess the threat of theaforementioned
   attacks on the use of cryptographic hashes in Internet protocols .
   This document analyzes the hash usage in SEND following the approach
   recommended by [RFC4270] and [NEW-HASHES].

   The following sections discuss the various aspects of hash usage in
   SEND and determine whether they are affected by the attacks on the
   underlying hash functions.

3.1.  Attacks against CGAs used in SEND

   Cryptographically Generated Addresses (CGAs) are defined in [RFC3972]
   and are used to securely associate a cryptographic public key with an
   IPv6 address in the SEND protocol.  Impacts of collision attacks on
   current uses of CGAs are analyzed in [RFC4982].  The basic idea
   behind collision attacks, as described in Section 4 of [RFC4270], is
   on the non-repudiation feature of hash algorithms.  Since CGAs do not
   provide non-repudiation features anyway.  Therefore, as [RFC4982]
   points out CGA based protocols, including SEND, are not affected by
   collision attacks on hash functions.  If pre-image attacks were to
   become feasible, an attacker can find new CGA Parameters that can
   generate the same CGA as the victim.  This class of attacks could be
   potentially dangerous since the security of SEND messages relies on
   the strength of the CGA.




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3.2.  Attacks against PKIX certificates in Authorization Delegation
      Discovery process

   To protect Router Discovery, SEND requires that routers be authorized
   to act as routers.  Routers are authorized by provisioning them with
   certificates from a trust anchor, and the hosts are configured with
   the trust anchor(s) used to authorize routers.  Researchers
   demonstrated attacks against PKIX certificates with MD5 signatures in
   2005 [NEW-HASHES] and in 2007 [X509-COLL].  An attacker can take
   advantage of these vulnerabilities to obtain an certificate with a
   different identity and use the certificate to impersonate a router.
   For this attack to succeed the attacker needs to predict the content
   of all fields (some of them are human-readable) appearing before the
   public key including the serial number and validity periods.  Even
   though a relying party cannot verify the content of these fields, the
   CA can identify the forged certificate, if necessary.

3.3.  Attacks against the Digital Signature in the SEND RSA Signature
      option

   The digital signature in the RSA Signature option is produced by
   signing, with the sender's private key, the SHA-1 hash over certain
   fields in the Neighbor Discovery message as described in Section 5.2
   of [RFC3971].  It is possible for an attacker to come up with two
   different Neighbor Discovery messages m and m' that result in the
   same value in the Digital Signature field.  Since the structure of
   the Neighbor Discovery messages is well defined, it is not possible
   to use this vulnerability in real world attacks.

3.4.  Attacks against the Key Hash field of the SEND RSA Signature
      option

   The SEND RSA signature option described in Section 5.2 of [RFC3971]
   defines a Key Hash field.  This field contains a SHA-1 hash of the
   public key that was used to generate the CGA.  To use a collision
   attack on this field, the attacker needs to come up with another
   public key (k') that produces the same hash as the real key (k).  But
   the real key (k) is already authorized through a parallel mechanism
   (either CGAs or router certificates).  Hence collision attacks are
   not possible on the Key Hash field.  Pre-image attacks on the Key
   Hash field are not useful for the same reason (any other key that
   hashes into the same Key Hash value will be detected due to a
   mismatch with the CGA or the router certificate).


4.  Conclusion

   Current attacks on hash functions do not constitute any practical



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   threat to the digital signatures used in SEND (both in the RSA
   signature option and in the X.509 certificates).  Attacks on CGAs, as
   described in [RFC4982], will compromise the security of SEND and they
   need to be addressed by encoding the hash algorithm information into
   the CGA as specified in [RFC4982].


5.  Security Considerations

   This document analyzes the impact that the attacks against hash
   functions hash attacks have on SEND.  It concludes that the only
   practical attack on SEND stems from a successful attack on an
   underlying CGA.  It does not add any new vulnerabilities to SEND.


6.  Acknowledgements

   The authors would like to thank Lars Eggert, Pete McCann, Julien
   Laganier, Jari Arkko, Paul Hoffman, Pasi Eronen, Adrian Farrel, Dan
   Romascanu, Tim Pol, Richard Woundy and Marcelo Bagnulo for reviewing
   earlier versions of this document and providing comments to make it
   better.


7.  References

7.1.  Normative References

   [NEW-HASHES]
              Bellovin, S. and E. Rescorla, "Deploying a New Hash
              Algorithm", November 2005.

   [RFC4270]  Hoffman, P. and B. Schneier, "Attacks on Cryptographic
              Hashes in Internet Protocols", RFC 4270, November 2005.

   [RFC4982]  Bagnulo, M. and J. Arkko, "Support for Multiple Hash
              Algorithms in Cryptographically Generated Addresses
              (CGAs)", RFC 4982, July 2007.

7.2.  Informative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [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)",



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              RFC 3972, March 2005.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [SHA1]     NIST, FIBS PUB 180-1, "Secure Hash Standard", April 1995.

   [SHA1-COLL]
              Wang, X., Yin, L., and H. Yu, "Finding Collisions in the
              Full SHA-1. CRYPTO 2005: 17-36", 2005.

   [X509-COLL]
              Stevens, M., Lenstra, A., and B. Weger, "Chosen-Prefix
              Collisions for MD5 and Colliding X.509 Certificates for
              Different Identitites. EUROCRYPT 2007: 1-22", 2005.


Authors' Addresses

   Ana Kukec
   University of Zagreb
   Unska 3
   Zagreb
   Croatia

   Email: ana.kukec@fer.hr


   Suresh Krishnan
   Ericsson
   8400 Decarie Blvd.
   Town of Mount Royal, QC
   Canada

   Email: suresh.krishnan@ericsson.com


   Sheng Jiang
   Huawei Technologies Co., Ltd
   KuiKe Building, No.9 Xinxi Rd.,
   Shang-Di Information Industry Base, Hai-Dian District, Beijing
   P.R. China

   Email: shengjiang@huawei.com





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