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PROPOSED STANDARD
Errata Exist
Internet Engineering Task Force (IETF)                        T. Kivinen
Request for Comments: 7427                                 INSIDE Secure
Updates: 7296                                                  J. Snyder
Category: Standards Track                                       Opus One
ISSN: 2070-1721                                             January 2015


Signature Authentication in the Internet Key Exchange Version 2 (IKEv2)

Abstract

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

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7427.

Copyright Notice

   Copyright (c) 2015 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
   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.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Authentication Payload  . . . . . . . . . . . . . . . . . . .   4
   4.  Hash Algorithm Notification . . . . . . . . . . . . . . . . .   6
   5.  Selecting the Public Key Algorithm  . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  10
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  10
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  10
   Appendix A.  Commonly Used ASN.1 Objects  . . . . . . . . . . . .  12
     A.1.  PKCS#1 1.5 RSA Encryption . . . . . . . . . . . . . . . .  12
       A.1.1.  sha1WithRSAEncryption . . . . . . . . . . . . . . . .  12
       A.1.2.  sha256WithRSAEncryption . . . . . . . . . . . . . . .  12
       A.1.3.  sha384WithRSAEncryption . . . . . . . . . . . . . . .  13
       A.1.4.  sha512WithRSAEncryption . . . . . . . . . . . . . . .  13
     A.2.  DSA . . . . . . . . . . . . . . . . . . . . . . . . . . .  13
       A.2.1.  dsa-with-sha1 . . . . . . . . . . . . . . . . . . . .  13
       A.2.2.  dsa-with-sha256 . . . . . . . . . . . . . . . . . . .  14
     A.3.  ECDSA . . . . . . . . . . . . . . . . . . . . . . . . . .  14
       A.3.1.  ecdsa-with-sha1 . . . . . . . . . . . . . . . . . . .  14
       A.3.2.  ecdsa-with-sha256 . . . . . . . . . . . . . . . . . .  14
       A.3.3.  ecdsa-with-sha384 . . . . . . . . . . . . . . . . . .  15
       A.3.4.  ecdsa-with-sha512 . . . . . . . . . . . . . . . . . .  15
     A.4.  RSASSA-PSS  . . . . . . . . . . . . . . . . . . . . . . .  15
       A.4.1.  RSASSA-PSS with Empty Parameters  . . . . . . . . . .  15
       A.4.2.  RSASSA-PSS with Default Parameters  . . . . . . . . .  16
       A.4.3.  RSASSA-PSS with SHA-256 . . . . . . . . . . . . . . .  17
   Appendix B.  IKEv2 Payload Example  . . . . . . . . . . . . . . .  17
     B.1.  sha1WithRSAEncryption . . . . . . . . . . . . . . . . . .  17
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  18
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  18

1.  Introduction

   This document adds a new IKEv2 [RFC7296] authentication method to
   support signature methods in a more general way.  The current
   signature-based authentication methods in 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 is cumbersome when
   more signature algorithms, hash algorithms, and elliptic curves need
   to be supported:






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   o  In IKEv2, authentication using RSA digital signatures calls for
      padding based on RSASSA-PKCS1-v1_5, although the newer RSASSA-PSS
      padding method is now recommended.  (See Section 5 of "Additional
      Algorithms and Identifiers for RSA Cryptography for use in PKIX
      Profile" [RFC4055].)

   o  With ECDSA and the Digital Signature Standard (DSS), there is no
      way to extract the hash algorithm from the signature.  Thus, for
      each new hash function to be supported with ECDSA or DSA, new
      authentication methods would be needed.  Support for new hash
      functions is particularly needed for DSS, because the current
      restriction to SHA-1 limits its security, meaning there is no
      point of using long keys with SHA-1.

   o  The tying of ECDSA authentication methods to particular elliptic
      curve groups requires definition of additional methods for each
      new group.  The combination of new ECDSA groups and hash functions
      will cause the number of required authentication methods to become
      unmanageable.  Furthermore, the restriction of ECDSA
      authentication to a specific group is inconsistent with the
      approach taken with DSS.

   With the selection of SHA-3, it might be possible that a signature
   method can be used with either SHA-3 or SHA-2.  This means that a new
   mechanism for negotiating the hash algorithm for a signature
   algorithm is needed.

   This document specifies two things:

   1.  A new authentication method that includes enough information
       inside the Authentication payload data so the signature hash
       algorithm can be extracted (see Section 3).

   2.  A method to indicate supported signature hash algorithms (see
       Section 4).  This allows the 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 requirement to actually
       negotiate one common hash algorithm, as different hash algorithms
       can be used in different directions if needed.

   The new digital signature method is flexible enough to include all
   current signature methods (RSA, DSA, ECDSA, RSASSA-PSS, etc.) and add
   new methods (ECGDSA, ElGamal, etc.) in the future.  To support this
   flexibility, the signature algorithm is specified in the same way
   that PKIX [RFC5280] specifies the signature of the Digital
   Certificate, by placing a simple ASN.1 object before the actual
   signature data.  This ASN.1 object contains an OID specifying the
   algorithm and associated parameters.  When an IKEv2 implementation



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   supports a fixed set of signature methods with commonly used
   parameters, it is acceptable for the implementation to treat the
   ASN.1 object as a binary blob that can be compared against the fixed
   set of known values.  IKEv2 implementations can also parse the ASN.1
   and extract the signature algorithm and associated parameters.

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 a new "Digital Signature" authentication
   method.  This method can be used with any type of signature.  As the
   authentication methods are not negotiated in IKEv2, the peer is only
   allowed to use this authentication method if the Notify payload of
   type SIGNATURE_HASH_ALGORITHMS has been sent and received by each
   peer.

   In this authentication method, the Authentication Data field inside
   the Authentication payload does not just include the signature value,
   as do other existing IKEv2 Authentication payloads.  Instead, the
   signature value is prefixed with an ASN.1 object indicating the
   algorithm used to generate the signature.  The ASN.1 object contains
   the algorithm identification OID, which identifies both the signature
   algorithm and the hash used when calculating the signature.  In
   addition to the OID, the ASN.1 object can contain optional parameters
   that might be needed for algorithms such as RSASSA-PSS (see
   Section 8.1 of [RFC3447]).

   To make implementations easier, the ASN.1 object is prefixed by the
   8-bit length field.  This length field allows simple implementations
   to know the length of the ASN.1 object without the need to parse it,
   so they can use it as a binary blob to be compared against known
   signature algorithm ASN.1 objects.  Thus, simple implementations may
   not need to be able to parse or generate ASN.1 objects.  See
   Appendix A for commonly used ASN.1 objects.

   The ASN.1 used here is the same ASN.1 used in the AlgorithmIdentifier
   of PKIX (see Section 4.1.1.2 of [RFC5280]), encoded using
   distinguished encoding rules (DER) [CCITT.X690.2002].  The algorithm
   OID inside the ASN.1 specifies the signature algorithm and the hash
   function, both of which are needed for signature verification.

   Currently, only the RSASSA-PSS signature algorithm uses the optional
   parameters.  For other signature algorithms, the parameters are



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   either NULL or missing.  Note that for some algorithms there are two
   possible ASN.1 encodings, one with optional parameters included but
   set to NULL and the other where the optional parameters are omitted.
   These dual encodings exist because of the way those algorithms are
   specified.  When encoding the ASN.1, implementations SHOULD use the
   preferred format called for by the algorithm specification.  If the
   algorithm specification says "preferredPresent", then the parameters
   object needs to be present, although it will be NULL if no parameters
   are specified.  If the algorithm specification says
   "preferredAbsent", then the entire optional parameters object is
   missing.

   The Authentication payload is defined in IKEv2 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | 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                      14

      Computed as specified in Section 2.15 of [RFC7296] using a private
      key associated with the public key sent in the Certificate payload
      and using one of the hash algorithms sent by the other end in the
      Notify payload of type SIGNATURE_HASH_ALGORITHMS.  If both ends
      send and receive SIGNATURE_HASH_ALGORITHMS Notify payloads, and
      signature authentication is to be used, then the authentication
      method specified in this Authentication payload MUST be used.  The
      format of the Authentication Data field is different from other
      Authentication methods and is specified below.

   o  Authentication Data (variable length) - See Section 2.15 of
      [RFC7296].  For "Digital Signature" format, the Authentication
      Data is formatted 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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | ASN.1 Length  | AlgorithmIdentifier ASN.1 object              |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~        AlgorithmIdentifier ASN.1 object continuing            ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                         Signature Value                       ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 2: Authentication Data Format

      *  ASN.1 Length (1 octet) - This field contains the length of the
         ASN.1-encoded AlgorithmIdentifier object.

      *  Algorithm Identifier (variable length) - This field contains
         the AlgorithmIdentifier ASN.1 object.

      *  Signature Value (variable length) - This field contains the
         actual signature value.

      There is no padding between the ASN.1 object and the signature
      value.  For hash truncation, the method specified in ANSI
      X9.62:2005 [X9.62] MUST be used.

4.  Hash Algorithm Notification

   The supported hash algorithms that can be used for the signature
   algorithms are indicated with a Notify payload of type
   SIGNATURE_HASH_ALGORITHMS sent inside the IKE_SA_INIT exchange.

   This notification also implicitly indicates support of the new
   "Digital Signature" algorithm method, as well as the list of hash
   functions supported by the sending peer.

   Both ends send their list of supported hash algorithms.  When
   calculating the digital 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 indicating the selected
   hash algorithm (and signature algorithm) used when calculating the
   signature is sent inside the Authentication Data field of the
   Authentication payload (with Auth Method of "Digital Signature" as
   defined above).




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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        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Protocol ID  |   SPI Size    |      Notify Message Type      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                Security Parameter Index (SPI)                 ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                                                               |
      ~                       Notification Data                       ~
      |                                                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 3: Notify Payload Format

   The Notify payload format is defined in Section 3.10 of [RFC7296].
   When a Notify payload of type SIGNATURE_HASH_ALGORITHMS is sent, the
   Protocol ID field is set to 0, the SPI Size is set to 0, and the
   Notify Message Type is set to 16431.

   The Notification Data field contains the list of 16-bit hash
   algorithm identifiers from the Hash Algorithm Identifiers of IANA's
   "Internet Key Exchange Version 2 (IKEv2) Parameters" registry.  There
   is no padding between the hash algorithm identifiers.

5.  Selecting the Public Key Algorithm

   This specification does not provide a way for the peers to indicate
   the public/private key pair types they have.  This raises the
   question of how the responder selects a public/private key pair type
   that the initiator supports.  This information can be found by
   several methods.

   One method to signal the key the initiator wants the responder to use
   is to indicate that in the IDr (Identification - Responder) payload
   of the IKE_AUTH request sent by the initiator.  In this case, the
   initiator indicates that it wants the responder to use a particular
   public/private key pair by sending an IDr payload that indicates that
   information.  In this case, the responder has different identities
   configured, with each of those identities associated to a public/
   private key or key type.

   Another method to ascertain the key the initiator wants the responder
   to use is through a Certificate Request payload sent by the
   initiator.  For example, the initiator could indicate in the



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   Certificate Request payload that it trusts a certificate authority
   certificate signed by an ECDSA key.  This indication implies that the
   initiator can process ECDSA signatures, which means that the
   responder can safely use ECDSA keys when authenticating.

   A third method is for the responder to check the key type used by the
   initiator and use the same key type that the initiator used.  This
   method does not work if the initiator is using shared secret or
   Extensible Authentication Protocol (EAP) authentication (i.e., is not
   using public keys).  If the initiator is using public key
   authentication, this method is the best way for the responder to
   ascertain the type of key the initiator supports.

   If the initiator uses a public key type that the responder does not
   support, the responder replies with a Notify message with error type
   AUTHENTICATION_FAILED.  If the initiator has multiple different keys,
   it may try a different key (and perhaps a different key type) until
   it finds a key that the other end accepts.  The initiator can also
   use the Certificate Request payload sent by the responder to help
   decide which public key should be tried.  In normal cases, when the
   initiator has multiple public keys, out-of-band configuration is used
   to select a public key for each connection.

6.  Security Considerations

   Tables 2 and 3 of the "Recommendations for Key Management"
   [NIST800-57] give recommendations for how to select suitable hash
   functions for the signature.

   This new digital signature method does not tie the Elliptic Curve to
   a specific hash function, which was done in the old IKEv2 ECDSA
   methods.  This means it is possible to mix different security levels.
   For example, it is possible to use a 512-bit Elliptic Curve with
   SHA1.  This means that the security of the authentication method is
   the security of the weakest component (signature algorithm, hash
   algorithm, or curve).  This complicates the security analysis of the
   system.

   IKEv2 peers have a series of policy databases (see Section 4.4 of
   [RFC4301]) that define which security algorithms and methods should
   be used during establishment of security associations.  To help end
   users select the desired security levels for communications protected
   by IPsec, implementers may wish to provide a mechanism in the IKE
   policy databases to limit the mixing of security levels or to
   restrict combinations of protocols.

   Security downgrade attacks, where more secure methods are deleted or
   modified from a payload by a man-in-the-middle to force lower levels



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   of security, are not a significant concern in IKEv2 Authentication
   payloads, as discussed in this RFC.  This is because a modified AUTH
   payload will be detected when the peer computes a signature over the
   IKE messages.

   One specific class of downgrade attacks requires selection of
   catastrophically weak ciphers.  In this type of attack, the man-in-
   the-middle attacker is able to "break" the cryptography in real time.
   This type of downgrade attack should be blocked by policy regarding
   cipher algorithm selection, as discussed above.

   The hash algorithm registry does not include MD5 as a supported hash
   algorithm, as it is not considered safe enough for signature use
   [WY05].

   The current IKEv2 protocol uses RSASSA-PKCS1-v1_5, which has known
   security vulnerabilities [KA08] [ME01] and does not allow using newer
   padding methods such as RSASSA-PSS.  The new method described in this
   RFC allows the use of other padding methods.

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

7.  IANA Considerations

   This document creates a new IANA registry for IKEv2 Hash Algorithms.
   Changes and additions to this registry are by Expert Review
   [RFC5226].

   The initial values of this registry are:

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

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

   Values 5-1023 are Unassigned.  Values 1024-65535 are reserved for
   Private Use among mutually consenting parties.





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   This specification also adds a new value for
   SIGNATURE_HASH_ALGORITHMS (16431) to the "IKEv2 Notify Message Types
   - Status Types" registry and adds a new value for Digital Signature
   (14) to the "IKEv2 Authentication Method" registry.

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,
              <http://www.rfc-editor.org/info/rfc2119>.

   [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,
              <http://www.rfc-editor.org/info/rfc5280>.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", RFC 7296, October 2014,
              <http://www.rfc-editor.org/info/rfc7296>.

8.2.  Informative References

   [CCITT.X690.2002]
              International Telephone and Telegraph Consultative
              Committee, "ASN.1 encoding rules: Specification of basic
              encoding Rules (BER), Canonical encoding rules (CER) and
              Distinguished encoding rules (DER)", CCITT Recommendation
              X.690, July 2002.

   [KA08]     Kuehn, U., Pyshkin, A., Tews, E., and R. Weinmann,
              "Variants of Bleichenbacher's Low-Exponent Attack on
              PKCS#1 RSA Signatures", Proceedings of Sicherheit 2008,
              pp.97-109, 2008.

   [ME01]     Menezes, A., "Evaluation of Security Level of
              Cryptography: RSA-OAEP, RSA-PSS, RSA Signature", December
              2001.

   [NIST800-57]
              Barker, E., Barker, W., Burr, W., Polk, W., and M. Smid,
              "Recommendation for Key Management - Part 1: General
              (Revised)", NIST Special Publication 800-57, March 2007.





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   [RFC3279]  Bassham, L., Polk, W., and R. Housley, "Algorithms and
              Identifiers for the Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 3279, April 2002,
              <http://www.rfc-editor.org/info/rfc3279>.

   [RFC3447]  Jonsson, J. and B. Kaliski, "Public-Key Cryptography
              Standards (PKCS) #1: RSA Cryptography Specifications
              Version 2.1", RFC 3447, February 2003,
              <http://www.rfc-editor.org/info/rfc3447>.

   [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, <http://www.rfc-editor.org/info/rfc4055>.

   [RFC4301]  Kent, S. and K. Seo, "Security Architecture for the
              Internet Protocol", RFC 4301, December 2005,
              <http://www.rfc-editor.org/info/rfc4301>.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs)", BCP 26, RFC 5226,
              May 2008, <http://www.rfc-editor.org/info/rfc5226>.

   [RFC5480]  Turner, S., Brown, D., Yiu, K., Housley, R., and T. Polk,
              "Elliptic Curve Cryptography Subject Public Key
              Information", RFC 5480, March 2009,
              <http://www.rfc-editor.org/info/rfc5480>.

   [RFC5758]  Dang, Q., Santesson, S., Moriarty, K., Brown, D., and T.
              Polk, "Internet X.509 Public Key Infrastructure:
              Additional Algorithms and Identifiers for DSA and ECDSA",
              RFC 5758, January 2010,
              <http://www.rfc-editor.org/info/rfc5758>.

   [RFC5912]  Hoffman, P. and J. Schaad, "New ASN.1 Modules for the
              Public Key Infrastructure Using X.509 (PKIX)", RFC 5912,
              June 2010, <http://www.rfc-editor.org/info/rfc5912>.

   [WY05]     Wang, X. and H. Yu, "How to break MD5 and other hash
              functions", Proceedings of EuroCrypt 2005, Lecture Notes
              in Computer Science Vol. 3494, 2005.

   [X9.62]    American National Standards Institute, "Public Key
              Cryptography for the Financial Services Industry: The
              Elliptic Curve Digital Signature Algorithm (ECDSA)", ANSI
              X9.62, November 2005.



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Appendix A.  Commonly Used ASN.1 Objects

   This section lists commonly used ASN.1 objects in binary form.  This
   section is not normative, and these values should only be used as
   examples.  If the ASN.1 object listed in Appendix A and the ASN.1
   object specified by the algorithm differ, then the algorithm
   specification must be used.  These values are taken from "New ASN.1
   Modules for the Public Key Infrastructure Using X.509 (PKIX)"
   [RFC5912].

A.1.  PKCS#1 1.5 RSA Encryption

   The algorithm identifiers here include several different ASN.1
   objects with different hash algorithms.  This document only includes
   the commonly used ones, i.e., the ones using SHA-1 or SHA-2 as the
   hash function.  Some other algorithms (such as MD2 and MD5) are not
   safe enough to be used as signature hash algorithms and are omitted.
   The IANA registry does not have code points for these other
   algorithms with RSA Encryption.  Note that there are no optional
   parameters in any of these algorithm identifiers, but all included
   here need NULL optional parameters present in the ASN.1.

   See "Algorithms and Identifiers for PKIX Profile" [RFC3279] and
   "Additional Algorithms and Identifiers for RSA Cryptography for use
   in the Internet X.509 Public Key Infrastructure Certificate and
   Certificate Revocation List (CRL) Profile" [RFC4055] for more
   information.

A.1.1.  sha1WithRSAEncryption

   sha1WithRSAEncryption OBJECT IDENTIFIER ::= { iso(1) member-body(2)
   us(840) rsadsi(113549) pkcs(1) pkcs-1(1) 5 }

   Parameters are required, and they must be NULL.

   Name = sha1WithRSAEncryption, oid = 1.2.840.113549.1.1.5
   Length = 15
   0000: 300d 0609 2a86 4886 f70d 0101 0505 00

A.1.2.  sha256WithRSAEncryption

   sha256WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 11 }

   Parameters are required, and they must be NULL.

   Name = sha256WithRSAEncryption, oid = 1.2.840.113549.1.1.11
   Length = 15
   0000: 300d 0609 2a86 4886 f70d 0101 0b05 00



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A.1.3.  sha384WithRSAEncryption

   sha384WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 12 }

   Parameters are required, and they must be NULL.

   Name = sha384WithRSAEncryption, oid = 1.2.840.113549.1.1.12
   Length = 15
   0000: 300d 0609 2a86 4886 f70d 0101 0c05 00

A.1.4.  sha512WithRSAEncryption

   sha512WithRSAEncryption OBJECT IDENTIFIER ::= { pkcs-1 13 }

   Parameters are required, and they must be NULL.

   Name = sha512WithRSAEncryption, oid = 1.2.840.113549.1.1.13
   Length = 15
   0000: 300d 0609 2a86 4886 f70d 0101 0d05 00

A.2.  DSA

   With DSA algorithms, optional parameters are always omitted.  Only
   algorithm combinations for DSA that are listed in the IANA registry
   are included.

   See "Algorithms and Identifiers for PKIX Profile" [RFC3279] and "PKIX
   Additional Algorithms and Identifiers for DSA and ECDSA" [RFC5758]
   for more information.

A.2.1.  dsa-with-sha1

   dsa-with-sha1 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
   x9-57(10040) x9algorithm(4) 3 }

   Parameters are absent.

   Name = dsa-with-sha1, oid = 1.2.840.10040.4.3
   Length = 11
   0000: 3009 0607 2a86 48ce 3804 03











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A.2.2.  dsa-with-sha256

   dsa-with-sha256 OBJECT IDENTIFIER ::= { joint-iso-ccitt(2)
   country(16) us(840) organization(1) gov(101) csor(3) algorithms(4)
   id-dsa-with-sha2(3) 2 }

   Parameters are absent.

   Name = dsa-with-sha256, oid = 2.16.840.1.101.3.4.3.2
   Length = 13
   0000: 300b 0609 6086 4801 6503 0403 02

A.3.  ECDSA

   With ECDSA algorithms, the optional parameters are always omitted.
   Only algorithm combinations for the ECDSA listed in the IANA registry
   are included.

   See "Elliptic Curve Cryptography Subject Public Key Information"
   [RFC5480], "Algorithms and Identifiers for PKIX Profile" [RFC3279],
   and "PKIX Additional Algorithms and Identifiers for DSA and ECDSA"
   [RFC5758] for more information.

A.3.1.  ecdsa-with-sha1

   ecdsa-with-SHA1 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
   ansi-X9-62(10045) signatures(4) 1 }

   Parameters are absent.

   Name = ecdsa-with-sha1, oid = 1.2.840.10045.4.1
   Length = 11
   0000: 3009 0607 2a86 48ce 3d04 01

A.3.2.  ecdsa-with-sha256

   ecdsa-with-SHA256 OBJECT IDENTIFIER ::= { iso(1) member-body(2)
   us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-SHA2(3) 2 }

   Parameters are absent.

   Name = ecdsa-with-sha256, oid = 1.2.840.10045.4.3.2
   Length = 12
   0000: 300a 0608 2a86 48ce 3d04 0302







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A.3.3.  ecdsa-with-sha384

   ecdsa-with-SHA384 OBJECT IDENTIFIER ::= { iso(1) member-body(2)
   us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-SHA2(3) 3 }

   Parameters are absent.

   Name = ecdsa-with-sha384, oid = 1.2.840.10045.4.3.3
   Length = 12
   0000: 300a 0608 2a86 48ce 3d04 0303

A.3.4.  ecdsa-with-sha512

   ecdsa-with-SHA512 OBJECT IDENTIFIER ::= { iso(1) member-body(2)
   us(840) ansi-X9-62(10045) signatures(4) ecdsa-with-SHA2(3) 4 }

   Parameters are absent.

   Name = ecdsa-with-sha512, oid = 1.2.840.10045.4.3.4
   Length = 12
   0000: 300a 0608 2a86 48ce 3d04 0304

A.4.  RSASSA-PSS

   With RSASSA-PSS, the algorithm object identifier must always be
   id-RSASSA-PSS, and the hash function and padding parameters are
   conveyed in the parameters (which are not optional in this case).
   See Additional RSA Algorithms and Identifiers [RFC4055] for more
   information.

A.4.1.  RSASSA-PSS with Empty Parameters

   id-RSASSA-PSS OBJECT IDENTIFIER ::= { pkcs-1 10 }

   Parameters are empty, but the ASN.1 part of the sequence must be
   present.  This means default parameters are used.

   0000 : SEQUENCE
   0002 :   OBJECT IDENTIFIER  RSASSA-PSS (1.2.840.113549.1.1.10)
   000d :   SEQUENCE

   Length = 15
   0000: 300d 0609 2a86 4886 f70d 0101 0a30 00








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A.4.2.  RSASSA-PSS with Default Parameters

   id-RSASSA-PSS OBJECT IDENTIFIER ::= { pkcs-1 10 }

   Here the parameters are present and contain the default parameters,
   i.e., hashAlgorithm of SHA-1, maskGenAlgorithm of mgf1SHA1,
   saltLength of 20, and trailerField of 1.

   0000 : SEQUENCE
   0002 :   OBJECT IDENTIFIER  RSASSA-PSS (1.2.840.113549.1.1.10)
   000d :   SEQUENCE
   000f :     CONTEXT 0
   0011 :       SEQUENCE
   0013 :         OBJECT IDENTIFIER  id-sha1 (1.3.14.3.2.26)
   001a :         NULL
   001c :     CONTEXT 1
   001e :       SEQUENCE
   0020 :         OBJECT IDENTIFIER  1.2.840.113549.1.1.8
   002b :         SEQUENCE
   002d :           OBJECT IDENTIFIER  id-sha1 (1.3.14.3.2.26)
   0034 :           NULL
   0036 :     CONTEXT 2
   0038 :       INTEGER   0x14 (5 bits)
   003b :     CONTEXT 3
   003d :       INTEGER   0x1 (1 bits)

   Name = RSASSA-PSS with default parameters,
          oid = 1.2.840.113549.1.1.10
   Length = 64
   0000: 303e 0609 2a86 4886 f70d 0101 0a30 31a0
   0010: 0b30 0906 052b 0e03 021a 0500 a118 3016
   0020: 0609 2a86 4886 f70d 0101 0830 0906 052b
   0030: 0e03 021a 0500 a203 0201 14a3 0302 0101


















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A.4.3.  RSASSA-PSS with SHA-256

   id-RSASSA-PSS OBJECT IDENTIFIER ::= { pkcs-1 10 }

   Here the parameters are present and contain hashAlgorithm of SHA-256,
   maskGenAlgorithm of SHA-256, saltLength of 32, and trailerField of 1.

   0000 : SEQUENCE
   0002 :   OBJECT IDENTIFIER  RSASSA-PSS (1.2.840.113549.1.1.10)
   000d :   SEQUENCE
   000f :     CONTEXT 0
   0011 :       SEQUENCE
   0013 :         OBJECT IDENTIFIER  id-sha256 (2.16.840.1.101.3.4.2.1)
   001e :         NULL
   0020 :     CONTEXT 1
   0022 :       SEQUENCE
   0024 :         OBJECT IDENTIFIER  1.2.840.113549.1.1.8
   002f :         SEQUENCE
   0031 :           OBJECT IDENTIFIER id-sha256 (2.16.840.1.101.3.4.2.1)
   003c :           NULL
   003e :     CONTEXT 2
   0040 :       INTEGER   0x20 (6 bits)
   0043 :     CONTEXT 3
   0045 :       INTEGER   0x1 (1 bits)

   Name = RSASSA-PSS with sha-256, oid = 1.2.840.113549.1.1.10
   Length = 72
   0000: 3046 0609 2a86 4886 f70d 0101 0a30 39a0
   0010: 0f30 0d06 0960 8648 0165 0304 0201 0500
   0020: a11c 301a 0609 2a86 4886 f70d 0101 0830
   0030: 0d06 0960 8648 0165 0304 0201 0500 a203
   0040: 0201 20a3 0302 0101

Appendix B.  IKEv2 Payload Example

B.1.  sha1WithRSAEncryption

   The IKEv2 AUTH payload would start like this:

   00000000: NN00 00LL 0e00 0000 0f30 0d06 092a 8648
   00000010: 86f7 0d01 0105 0500 ....

   Where the NN will be the next payload type (i.e., the value depends
   on the next payload after this Authentication payload), the LL will
   be the length of this payload, and after the sha1WithRSAEncryption
   ASN.1 block (15 bytes) there will be the actual signature, which is
   omitted here.




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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 Harkins,
   Johannes Merkle, Tero Kivinen, David McGrew, and Yoav Nir.

Authors' Addresses

   Tero Kivinen
   INSIDE Secure
   Eerikinkatu 28
   Helsinki  FI-00180
   Finland

   EMail: kivinen@iki.fi


   Joel Snyder
   Opus One
   1404 East Lind Road
   Tucson, AZ  85719

   Phone: +1 520 324 0494
   EMail: jms@opus1.com



























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