Host Identity Protocol                                              Heer
Internet-Draft                           Distributed Systems Group, RWTH
Intended status: Experimental                          Aachen University
Expires: July 22, 2011                                          Varjonen
                                      Helsinki Institute for Information
                                                        January 18, 2011

                  Host Identity Protocol Certificates


   The CERT parameter is a container for X.509.v3 certificates and
   Simple Public Key Infrastructure (SPKI) certificates.  It is used for
   carrying these certificates in Host Identity Protocol (HIP) control
   packets.  This document specifies the certificate parameter and the
   error signaling in case of a failed verification.  Additionally, this
   document specifies the representations of Host Identity Tags in
   X.509.v3 and SPKI certificates.

   The concrete use of certificates including how certificates are
   obtained, requested, and which actions are taken upon successful or
   failed verification are specific to the scenario in which the
   certificates are used.  Hence, the definition of these scenario-
   specific aspects are left to the documents that use the CERT

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1.  Introduction

   Digital certificates bind a piece of information to a public key by
   means of a digital signature, and thus, enable the holder of a
   private key to generate cryptographically verifiable statements.  The
   Host Identity Protocol (HIP) [RFC5201] defines a new cryptographic
   namespace based on asymmetric cryptography.  The identity of each
   host is derived from a public key, allowing hosts to digitally sign
   data and issue certificates with their private key.  This document
   specifies the CERT parameter, which is used to transmit digital
   certificates in HIP.  It fills the placeholder specified in Section
   5.2 of [RFC5201].

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  CERT Parameter

   The CERT parameter is a container for certain types of digital
   certificates.  It MAY either carry SPKI certificates or X.509.v3
   certificates.  It does not specify any certificate semantics.
   However, it defines supplementary parameters that help HIP hosts to
   transmit semantically grouped CERT parameters in a more systematic
   way.  The specific use of the CERT parameter for different use cases
   is intentionally not discussed in this document because it is
   specific to a concrete use case.  Hence, the use of the CERT
   parameter will be defined in the documents that use the CERT

   The CERT parameter is covered, when present, by the HIP SIGNATURE
   field and is a non-critical parameter.

   The CERT parameter can be used in all HIP packets.  However, using it
   in the I1 packet is not recommended because it can increase the
   processing times of I1s, which can be problematic when processing
   storms of I1s.  Each HIP control packet MAY contain multiple CERT
   parameters.  These parameters MAY be related or unrelated.  Related
   certificates are managed in Cert groups.  A Cert group specifies a
   group of related CERT parameters that SHOULD be interpreted in a
   certain order (e.g., for expressing certificate chains).  For
   grouping CERT parameters, the Cert group and the Cert count field
   MUST be set.  Ungrouped certificates exhibit a unique Cert group
   field and set the Cert count to 1.  CERT parameters with the same
   Cert group number in the group field indicate a logical grouping.
   The Cert count field indicates the number of CERT parameters in the

   CERT parameters that belong to the same Cert group MAY be contained
   in multiple sequential HIP control packets.  This is indicated by a
   higher Cert count than the amount of CERT parameters with matching
   Cert group fields in a HIP control packet.  The CERT parameters MUST
   be placed in ascending order, within a HIP control packet, according
   to their Cert group field.  Cert groups MAY only span multiple
   packets if the Cert group does not fit the packet.  A HIP packet MUST
   NOT contain more than one incomplete Cert group that continues in the
   next HIP control packet.

   The Cert ID acts as a sequence number to identify the certificates in
   a Cert group.  The numbers in the Cert ID field MUST start from 1 up
   to Cert count.

   The Cert Group and Cert ID namespaces are managed locally by each
   host that sends CERT parameters in HIP control packets.

     0                   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
     |             Type              |             Length            |
     |  Cert group   |  Cert count   |    Cert ID    |   Cert type   |
     |                          Certificate                          /
     /                               |            Padding            |

     Type          768
     Length        Length in octets, excluding Type, Length, and Padding
     Cert group    Group ID grouping multiple related CERT parameters
     Cert count    Total count of certificates that are sent, possibly
                   in several consecutive HIP control packets.
     Cert ID       The sequence number for this certificate
     Cert Type     Indicates the type of the certificate
     Padding       Any Padding, if necessary, to make the TLV a multiple
                   of 8 bytes.

   The following certificate types are defined:

             |           Cert format          | Type number |
             |            X.509.v3            |      1      |
             |              SPKI              |      2      |
             |    Hash and URL of X.509.v3    |      3      |
             |      Hash and URL of SPKI      |      4      |
             |      LDAP URL of X.509.v3      |      5      |
             |        LDAP URL of SPKI        |      6      |
             | Distinguished Name of X.509.v3 |      7      |
             |   Distinguished Name of SPKI   |      8      |

   The next sections outline the use of HITs in X.509.v3 and in SPKI
   certificates.  X.509.v3 certificates are defined in [RFC5280].  The
   wire format for X.509.v3 is Distinguished Encoding Rules format as
   defined in [X.690].  The SPKI and its formats are defined in

   Hash and URL encodings (3 and 4) are used as defined in [RFC5996]
   Section 3.6.  Using hash and URL encodings results in smaller HIP
   control packets, but requires the receiver to resolve the URL or
   check a local cache against the hash.

   LDAP URL encodings (5 and 6) are used as defined in [RFC4516].  Using
   LDAP URL encoding results in smaller HIP control packets but requires
   the receiver to retrieve the certificate or check a local cache
   against the URL.

   Distinguished name (DN) encodings (7 and 8) are used as defined in
   [RFC4514].  Using the DN encoding results in smaller HIP control
   packets, but requires the receiver to retrieve the certificate or
   check a local cache against the DN.

3.  X.509.v3 Certificate Object and Host Identities

   When using X.509.v3 certificates to transmit information related to
   HIP hosts, HITs MAY be enclosed within the certificates.  HITs can
   represent an issuer, a subject, or both.  In X.509.v3 HITs are
   represented as issuer or subject alternative name extensions as
   defined in [RFC5280].  If only the HIT of the host is presented as
   either the issuer or the subject the respective HIT MUST be placed
   into the respective entity's DN's Common Name (CN) section in a colon
   delimited presentation format defined in [RFC5952].  Inclusion of CN
   is not necessary if DN contains any other naming information.  It is
   RECOMMENDED to use the FQDN/NAI from the hosts HOST_ID parameter in
   the DN if one exists.  The full HIs are presented in the public key
   entries of X.509.v3 certificates.

   The following examples illustrate how HITs are presented as issuer
   and subject in the DN and in the X.509.v3 extension alternative

       Format of DN:
           Issuer: CN=hit-of-issuer
           Subject: CN=hit-of-subject

       Example DN:
           Issuer: CN=2001:14:6cf:fae7:bb79:bf78:7d64:c056
           Subject: CN=2001:1c:5a14:26de:a07c:385b:de35:60e3

       Format of X509v3 extensions:
           X509v3 Issuer Alternative Name:
               IP Address:hit-of-issuer
           X509v3 Subject Alternative Name:
               IP Address:hit-of-subject

       Example X509v3 extensions:
           X509v3 Issuer Alternative Name:
               IP Address:2001:14:6cf:fae7:bb79:bf78:7d64:c056
           X509v3 Subject Alternative Name:
               IP Address:2001:1C:5a14:26de:a07C:385b:de35:60e3

   Appendix B shows a full example X.509.v3 certificate with HIP

   As another example, consider a managed PKI environment in which the
   peers have certificates that are anchored in (potentially different)
   managed trust chains.  In this scenario, the certificates issued to
   HIP hosts are signed by intermediate Certificate Authorities (CAs) up
   to a root CA.  In this example, the managed PKI environment is
   neither HIP aware, nor can it be configured to compute HITs and
   include them in the certificates.

   In this scenario, it is RECOMMENDED that the HIP peers have and use
   some mechanism of defining trusted root CAs for the purpose of
   establishing HIP communications.  Furthermore it is recommended that
   the HIP peers have and use some mechanism of checking peer
   certificate validity for revocation, signature, minimum cryptographic
   strength, etc., up to the trusted root CA.

   When HIP communications are established, the HIP hosts not only need
   to send their identity certificates (or pointers to their
   certificates), but also the chain of intermediate CAs (or pointers to
   the CAs) up to the root CA, or to a CA that is trusted by the remote
   peer.  This chain of certificates MUST be sent in a Cert group as
   specified in Section 2.  The HIP peers validate each other's
   certificates and compute peer HITs based on the certificate public

4.  SPKI Cert Object and Host Identities

   When using SPKI certificates to transmit information related to HIP
   hosts, HITs need to be enclosed within the certificates.  HITs can
   represent an issuer, a subject, or both.  In the following we define
   the representation of those identifiers for SPKI given as
   S-expressions.  Note that the S-expressions are only the human-
   readable representation of SPKI certificates.  Full HIs are presented
   in the public key sequences of SPKI certificates.

   As an example the Host Identity Tag of a host is expressed as

       Format:  (hash hit hit-of-host)
       Example: (hash hit 2001:13:724d:f3c0:6ff0:33c2:15d8:5f50)

   Appendix A shows a full example SPKI certificate with HIP content.

5.  Revocation of Certificates

   Revocation of X.509.v3 certificates is handled as defined in Section
   5 of [RFC5280].  Revocation of SPKI certificates is handled as
   defined in Section 5 of [RFC2693].

6.  Error signaling

   If the Initiator does not send the certificate that the Responder
   requires the Responder may take actions (e.g. reject the connection).
   The Responder MAY signal this to the Initiator by sending a HIP
   NOTIFY message with NOTIFICATION parameter error type

   If the verification of a certificate fails, a verifier MAY signal
   this to the provider of the certificate by sending a HIP NOTIFY
   message with NOTIFICATION parameter error type INVALID_CERTIFICATE.

     ------------------------------------     -----

     CREDENTIALS_REQUIRED                      48

     The Responder is unwilling to set up an association
     as the Initiator did not send the needed credentials.

     INVALID_CERTIFICATE                       50

     Sent in response to a failed verification of a certificate.
     Notification Data MAY contain n groups of 2 octets (n calculated
     from the NOTIFICATION parameter length), in order Cert group and
     Cert ID of the certificate parameter that caused the failure.

7.  IANA Considerations

   This document defines the CERT parameter for the Host Identity
   Protocol [RFC5201].  This parameter is defined in Section 2 with type
   768.  The parameter type number is also defined in [RFC5201].

   The CERT parameter has 8-bit unsigned integer field for different
   certificate types, for which IANA is to create and maintain a new
   sub-registry entitled "HIP certificate types" under the "Host
   Identity Protocol (HIP) Parameters".  Initial values for the
   Certificate type registry are given in Section 2.

   In Section 6 this document defines two new types for "NOTIFY message
   types" sub-registry under "Host Identity Protocol (HIP) Parameters".

8.  Security Considerations

   Certificate grouping allows the certificates to be sent in multiple
   consecutive packets.  This might allow similar attacks as IP-layer
   fragmentation allows, for example sending of fragments in wrong order
   and skipping some fragments to delay or stall packet processing by
   the victim in order to use resources (e.g.  CPU or memory).  Hence,
   hosts SHOULD implement mechanisms to discard certificate groups with
   outstanding certificates if state space is scarce.

9.  Acknowledgements

   The authors would like to thank A. Keranen, D. Mattes, M. Komu and T.
   Henderson for the fruitful conversations on the subject.  D. Mattes
   most notably contributed the non-HIP aware use case in Section 3.

10.  References

10.1.  Normative References

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

   [RFC2693]  Ellison, C., Frantz, B., Lampson, B., Rivest, R., Thomas,
              B., and T. Ylonen, "SPKI Certificate Theory", RFC 2693,
              September 1999.

   [RFC4514]  Zeilenga, K., "Lightweight Directory Access Protocol
              (LDAP): String Representation of Distinguished Names",
              RFC 4514, June 2006.

   [RFC4516]  Smith, M. and T. Howes, "Lightweight Directory Access
              Protocol (LDAP): Uniform Resource Locator", RFC 4516,
              June 2006.

   [RFC5201]  Moskowitz, R., Nikander, P., Jokela, P., and T. Henderson,
              "Host Identity Protocol", RFC 5201, April 2008.

   [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.

   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952, August 2010.

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

10.2.  Informative References

   [X.690]    ITU-T, "Recommendation X.690 Information Technology -
              ASN.1 encoding rules: Specification of Basic Encoding
              Rules (BER), Canonical Encoding Rules (CER) and
              Distinguished Encoding Rules (DER)", July 2002, <http://

Appendix A.  SPKI certificate example

   This section shows a SPKI certificate with encoded HITs.  The example
   has been indented for readability.

         (e #010001#)
         (n |yDwznOwX0w+zvQbpWoTnfWrUPLKW2NFrpXbsIcH/QBSLb
           (hash hit 2001:15:2453:698a:9aa:253a:dcb5:981e)
           (hash hit 2001:12:ccd6:4715:72a3:2ab1:77e4:4acc)
         (not-before "2011-01-12_13:43:09")
         (not-after "2011-01-22_13:43:09")
         (hash sha1 |h5fC8HUMATTtK0cjYqIgeN3HCIMA|)

Appendix B.  X.509.v3 certificate example

   This section shows a X.509.v3 certificate with encoded HITs.

           Version: 3 (0x2)
           Serial Number: 0 (0x0)
           Signature Algorithm: sha1WithRSAEncryption
           Issuer: CN=2001:1e:d709:1980:5c6a:bb0c:7650:a027
               Not Before: Jun 22 13:39:32 2010 GMT
               Not After : Jul  2 13:39:32 2010 GMT
           Subject: CN=2001:1c:5a14:26de:a07c:385b:de35:60e3
           Subject Public Key Info:
               Public Key Algorithm: rsaEncryption
               RSA Public Key: (1024 bit)
                   Modulus (1024 bit):
                   Exponent: 65537 (0x10001)
           X509v3 extensions:
               X509v3 Issuer Alternative Name:
                   IP Address:2001:1e:d709:1980:5c6a:bb0C:7650:a027
               X509v3 Subject Alternative Name:
                   IP Address:2001:1c:5a14:26de:a07c:385b:de35:60e3
       Signature Algorithm: sha1WithRSAEncryption

Appendix C.  Change log

   Changes from version 00 to 01:

   o  Revised text on DN usage.

   o  Revised text on Cert group usage.

   Changes from version 01 to 02:

   o  Revised the type numbers.

   o  Added a section on signaling.

   Changes from version 02 to 03:

   o  Revised text on CERT usage in control packets.

   Changes from version 03 to 04:

   o  Added the non-HIP aware use case to the Section 3.

   o  Clarified that the HITs are not always required in the

   o  Rewrote the signaling section.

   o  LDAP URL to LDAP DN in Section 2 last paragraph.

   o  CERT is always covered by a signature as it's type number requires

   o  New example certificates

   o  Style and language clean-ups

   o  Changed IANA considerations

   o  Revised the type numbers

   o  RFC 2119 keywords

   o  Updated the IANA considerations section

   o  Rewrote the abstract

   Changes from version 04 to 05:

   o  Clarified the examples in Section 3.

   o  Clarifications to Section Section 3.

   o  Modified the explanation of INVALID_CERTIFICATE to allow multiple

   o  Added reference to the IPv6 colon delimited presentation format.

   o  Small editorial changes.

   Changes from version 05 to 06:

   o  Editorial changes.

   o  Unified the example in Section 3.

   Changes from version 06 to 07:

   o  Editorial changes.

   o  Removed a the second paragraph in section 8.

   o  Changed the example in Appendix A (Cert created without the
      leading zeroes in HITs).

   Changes from version 07 to 08:

   o  Updated and checked the references.

   Changes from version 08 to 09:

   o  Fixing boilerplate.

Authors' Addresses

   Tobias Heer
   Distributed Systems Group, RWTH Aachen University
   Ahornstrasse 55

   Phone: +49 241 80 214 36

   Samu Varjonen
   Helsinki Institute for Information Technology
   Gustaf Haellstroemin katu 2b