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Versions: 00 01 02 03 04 05 06 07 RFC 7427

IP Security Maintenance and Extensions                        T. Kivinen
(ipsecme)                                                  INSIDE Secure
Internet-Draft                                          December 4, 2012
Updates: RFC 5996 (if approved)
Intended status: Standards Track
Expires: June 7, 2013


                   Signature Authentication in IKEv2
              draft-kivinen-ipsecme-signature-auth-00.txt

Abstract

   The Internet Key Exchange Version 2 (IKEv2) protocol has limited
   support for the Elliptic Curve Digital Signature Algorithm (ECDSA).
   The current support only includes support for three Elliptic Curve
   groups, and there is fixed hash algorithm tied to each curve.  This
   document generalizes the IKEv2 signature support so it can support
   any signature method supported by the PKIX and also adds signature
   hash algorithm negotiation.  This generic mechanism is not limited to
   ECDSA, but can also be used with other signature algorithms.

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
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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on June 7, 2013.

Copyright Notice

   Copyright (c) 2012 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 . . . . . . . . . . . . . . . . . . . . . . . . . . 4
   3.  Authentication Payload  . . . . . . . . . . . . . . . . . . . . 4
   4.  Hash Algorithm Notification . . . . . . . . . . . . . . . . . . 6
   5.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     8.2.  Informative References  . . . . . . . . . . . . . . . . . . 8
   Appendix A.  Examples . . . . . . . . . . . . . . . . . . . . . . . 8
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 8






























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1.  Introduction

   This document adds support for new IKEv2 ([RFC5996]) authentication
   method to support all kinds of signature methods.  The current
   signature based authentication methods in the IKEv2 are per
   algorithm, i.e. there is one for RSA Digital signatures, one for DSS
   Digital Signatures (using SHA-1) and three for different ECDSA curves
   each tied to exactly one hash algorithm.  This design starts to be
   cumbersome when more ECDSA groups are added, as each of them would
   require new authentication method and as with ECDSA there is no way
   to extract the hash algorithm from the signature, each ECDSA
   algorithm would need to come with fixed hash algorithm tied to it.

   With the SHA-3 definitions coming out, it is seen that it might be
   possible that in the future the signature methods are used with SHA-3
   also, not only SHA-2.  This means new mechanism for negotiating the
   hash algorithm for the signature algorithms is needed.

   The RSA Digital Signatures format in the IKEv2 is specified to use
   RSASSA-PKCS1-v1_5, but there has been some discussions that newer
   padding methods should also be possible (See section 5 of [RFC4055]).
   The DSS Digital Signatures format in the IKEv2 is specified to always
   use SHA-1, which limits the security of that, meaning there is no
   point of using long keys with it.

   This documents specifies two things, one is one new authentication
   method, which includes the enough information inside the
   Authentication payload data that the signature hash algorithm can be
   extracted from there (see Section 3).  The another thing is to add
   indication of supported signature hash algorithms by the peer (see
   Section 4).  This allows peer to know which hash algorithms are
   supported by the other end and use one of them (provided one is
   allowed by policy).  There is no need to actually negotiate one
   common hash algorithm, as different hash algorithms can be used in
   different directions if needed.

   The new digital signature method needs to be flexible enough to
   include all current signature methods (ECDSA, ECGDSA, RSASSA-PSS,
   ElGamal, etc), and also allow adding new things in the future.  For
   this the signature algorithm is specified by and OID which specifies
   both the signature and hash algorithms (i.e. sha1WithRSAEncryption,
   dsa-with-sha1, dsa-with-sha256, ecdsa-with-SHA1, ecdsa-with-SHA256
   etc), meaning any signature and hash algorithm specified by an OID
   can be used.







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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 [RFC2119].


3.  Authentication Payload

   This document specifies new "Digital Signature" authentication
   method.  This method can be used with any types of signatures.  As
   the authentication methods are not negotiated in the IKEv2, the peer
   is only allowed to use this authentication method if the
   SIGNATURE_HASH_ALGORITHMS Notify Payload has been sent and received.

   In this newly defined authentication method, the Authentication Data
   field inside the Authentication Payload does not include only the
   signature value, but instead the signature value is prefixed with the
   algorithm identification OID.  This OID identifies both the signature
   algorithm and the hash used when calculating the signature.  To make
   implementations easier, the OID is prefixed by the 8-bit length
   field.  This length field allows simple implementations to be able to
   know the length of the OID, so they can use it as binary blob which
   is compared against the known OIDs, i.e. they do not need to be able
   to parse or generate ASN.1 DER OIDs (Note, that the 2nd byte of the
   ASN.1 DER OID, also includes the length, but adding it outside makes
   things bit easier for implementors).

   The OIDs used here are the same OIDs which are used inside the
   AlgorithmIdentifier of the PKIX (Section 4.1.1.2 of [RFC5280]), but
   only the algorithm OID is included, no parameters etc.  The EC curve
   is always known by the peer because it needs to have the certificate
   or the public key of the other end before it can do signature
   verification and public key specifies the curve.

      XXX While reading RFC4055, it seemed that the OID is not enough to
      specify the hash function used for the RSASSA-PSS, i.e. it seems
      that we would need to include full AlgorithmIdentifier ASN object,
      as it includes also the parameters, and the hash function is
      specified in the parameters.  Is my reading of RFC4055 correct?
      XXX

   The Authentication payload is defined in IKEv2 as follows:








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                           1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Next Payload  |C|  RESERVED   |         Payload Length        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Auth Method   |                RESERVED                       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                      Authentication Data                      ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 1: Authentication Payload Format.

   o  Auth Method (1 octet) - Specifies the method of authentication
      used.

      Mechanism                              Value
      -----------------------------------------------------------------
      Digital Signature                      <TBD>
         Computed as specified in Section 2.15 of RFC5996 using a
         private key associated with the public key sent in certificate
         payload, and using one of the hash algorithms sent by the other
         end in the SIGNATURE_HASH_ALGORITHMS notify payload. If both
         ends send and receive SIGNATURE_HASH_ALGORITHMS and signature
         authentication is to be used, then this method MUST be used.
         The Authentication Data field has bit different format than in
         other Authentication methods (see below).

   o  Authentication Data (variable length) - see Section 2.15 of
      RFC5996.  For "Digital Signature" format the Authentication data
      contains special format as follows:

                           1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | OID Length    | OID (0x06)    . OID value len . OID value     |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                      OID value continuing                     ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                         Signature Value                       ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                    Figure 2: Authentication Data Format.



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      Where the OID Length is the length of the ASN.1 encoded OID value,
      and after that is the actual Signature Algorithm OID followed by
      the actual signature value.  There is no padding between OID and
      signature value.  ASN.1 encoded OIDs always start with byte of
      0x06 followed by the length of the actual OID value (which is
      shown in the figure above).  For the hash truncation the method of
      X9.62, SEC1 and IO 14888-3 MUST be used.  XXX Need reference for
      X9.62/SEC1 etchere XXX.


4.  Hash Algorithm Notification

   The supported hash algorithms that can be used for the signature
   algorithms are now indicated with new SIGNATURE_HASH_ALGORITHMS
   Notification Payload sent inside the IKE_SA_INIT exchange.  This
   notification also indicates the support of the new signature
   algorithm method, i.e sending this notification tells that new
   "Digital Signature" authentication method is supported and that
   following hash functions are supported by sending peer.  Both ends
   sends their list of supported hash-algorithms and when calculating
   signature a peer MUST pick one algorithm sent by the other peer.
   Note, that different algorithms can be used in different directions.
   The algorithm OID matching selected hash algorithm (and signature
   algorithm) used when calculating the signature is sent inside the
   Authentication Data field of the Authentication Payload.

                               1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Next Payload  |C|  RESERVED   |         Payload Length        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Protocol ID  |   SPI Size    |      Notify Message Type      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                Security Parameter Index (SPI)                 ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       Notification Data                       ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 3: Notify Payload Format.

   Protocol ID is 0, SPI Size 0, and Notify Message Type <TBD from
   status types>.  The Notification Data value contains list of 16-bit
   hash algorithm identifiers from the newly created Hash Algorithm
   Identifiers for the IKEv2 IANA registry.



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5.  Security Considerations

      XXX The text about the guidance how to select suitable hash
      functions is missing here.  XXX

   This new digital signature method does not tie the EC curve to the
   specific hash function, which was done in the old IKEv2 ECDSA
   methods.  This means it is possible to use 512-bit EC curve with
   SHA1, i.e. this allows mixing different security levels.  This means
   that the security of the authentication method is the security of the
   weakest of components (signature algorithm, hash algorithm, curve).
   This might make the security analysis of the system bit more complex.
   Note, that this kind of mixing of the security can be disallowed by
   the policy.

   The hash algorithm registry does not include MD5 as supported hash
   algorithm, as it is not considered safe enough for signature use.

      XXX Need reference for MD5 considered unsafe.  XXX

   The current IKEv2 uses RSASSA-PKCS1-v1_5, and does not allow using
   newer padding methods like RSASSA-PSS.  This new method allows using
   other padding methods.

      XXX Need reference for RSASSA-PSS vs RSASSA-PKCS1-v1_5 security.
      XXX

   The current IKEv2 only allows using normal DSA with SHA-1, which
   means the security of the regular DSA is limited to the security of
   SHA-1.  This new methods allows using longer keys and longer hashes
   with DSA.


6.  IANA Considerations

   This document creates new IANA registry for IKEv2 Hash Algorithms.
   Changes and additions to this registry is by expert review.

   The initial values of this registry is:

   Hash Algorithm                       Value
   --------------                       -----
   RESERVED                             0
   SHA1                                 1
   SHA2-256                             2
   SHA2-384                             3
   SHA2-512                             4




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   MD5 is not included to the hash algorithm list as it is not
   considered safe enough for signature hash uses.

   Values 5-1023 are reserved to IANA.  Values 1024-65535 are for
   private use among mutually consenting parties.


7.  Acknowledgements

   Most of this work was based on the work done in the IPsecME design
   team for the ECDSA.  The design team members were: Dan Harking,
   Johannes Merkle, Tero Kivinen, David McGrew, and Yoav Nir.


8.  References

8.1.  Normative References

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

   [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.

   [RFC5996]  Kaufman, C., Hoffman, P., Nir, Y., and P. Eronen,
              "Internet Key Exchange Protocol Version 2 (IKEv2)",
              RFC 5996, September 2010.

8.2.  Informative References

   [RFC4055]  Schaad, J., Kaliski, B., and R. Housley, "Additional
              Algorithms and Identifiers for RSA Cryptography for use in
              the Internet X.509 Public Key Infrastructure Certificate
              and Certificate Revocation List (CRL) Profile", RFC 4055,
              June 2005.

   [RFC5480]  Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
              "Elliptic Curve Cryptography Subject Public Key
              Information", RFC 5480, March 2009.


Appendix A.  Examples







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Author's Address

   Tero Kivinen
   INSIDE Secure
   Eerikinkatu 28
   HELSINKI  FI-00180
   FI

   Email: kivinen@iki.fi










































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