Host Identity Protocol                                              Heer
Internet-Draft                             Communication and Distributed
Updates: 5201 (if approved)              Systems, RWTH Aachen University
Intended status: Experimental                                   Varjonen
Expires: September 10, 15, 2011           Helsinki Institute for Information
                                                          March 9, 14, 2011

                  Host Identity Protocol Certificates


   The CERT parameter is a container for digital 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 version 3 (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

   This document updates RFC 5201.

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   This Internet-Draft will expire on September 10, 15, 2011.

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1.  Introduction

   Digital certificates bind pieces 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], and thus, updates [RFC5201].

1.1.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "OPTIONAL" in this 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 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 and protected, 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 first Initiator (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 group.

   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 certificates MUST use the algorithms defined in [RFC5201] as the
   signature and hash algorithms.

   The following certificate types are defined:

             |           Cert format          | Type number |
             |            Reserved            |      0      |
             |            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 Host Identity Tags (HITs) in
   X.509 v3 and in Simple Public Key Infrastructure (SPKI) certificates.
   X.509 v3 certificates and the handling procedures are defined in
   [RFC5280].  The wire format for X.509 v3 is Distinguished Encoding
   Rules format as defined in [X.690].  The SPKI, the handling
   procedures, and the formats are defined in [RFC2693].

   Hash and Uniform Resource Locator (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, packets than by including the
   certificate(s), 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 represented by the
   string representation of the certificate's subject DN 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

   If needed, HITs can represent an issuer, a subject, or both in x.509
   v3.  HITs are represented as IPv6 addresses as defined in [RFC4843].
   When Host Identifier ( HI ) is used to sign the certificate the
   respective HIT MUST be placed in to the Issuer Alternative Name (IAN)
   extension using the GeneralName form iPAddress as defined in
   [RFC5280].  When the certificate is issued for a HIP host, identified
   by a HIT and HI, the respective HIT MUST be placed in to the Subject
   Alternative Name (SAN) extension using the GeneralName form iPAddress
   and the full HI is presented as the subjects public key info as
   defined in [RFC5280].

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

       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 Public Key Infrastructure
   (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 Certification 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

   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.  New values for the
   Certificate types from the unassigned space are assigned through IETF

   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.

   Checking of the URL and LDAP entries might allow DoS attacks, where
   the target host may be subjected to bogus work.

   Security considerations for SPKI certificates are discussed in
   [RFC2693] and for X.509 v3 in [RFC5280]

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.  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.

   [RFC4843]  Nikander, P., Laganier, J., and F. Dupont, "An IPv6 Prefix
              for Overlay Routable Cryptographic Hash Identifiers
              (ORCHID)", RFC 4843, April 2007.

   [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.

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

   [X.690]    ITU-T, "Recommendation X.690 (2002) | ISO/IEC 8825-1:2002,
              Information Technology - ASN.1 encoding rules:
              Specification of Basic Encoding Rules (BER), Canonical
              Encoding Rules (CER) and Distinguished Encoding Rules
              (DER)", July 2002.

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 CN=Example issuing host, DC=example, DC=com
               Not Before: Jun 22 13:39:32 2010 Mar 11 09:01:39 2011 GMT
               Not After : Jul  2 13:39:32 2010 Mar 21 09:01:39 2011 GMT
           Subject: CN=2001:1c:5a14:26de:a07c:385b:de35:60e3 CN=Example subject host, DC=example, DC=com
           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 Address:2001:13:8D83:41C5:DC9F:38ED:E742:7281
               X509v3 Subject Alternative Name:
                   IP Address:2001:1c:5a14:26de:a07c:385b:de35:60e3 Address:2001:1C:6E02:D3E0:9B90:8417:673E:99DB
       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.

   Changes from version 09 to 10:

   o  IANA considerations updated based on the IANA review.

   o  Updates based on the hip-chairs review.

   o  Updates based on the Gen-ART review.

   Changes from version 10 to 11:

   o  Fixed the nits.

   Changes from version 11 to 12:

   o  Updates based on the PKIX WG review.

Authors' Addresses

   Tobias Heer
   Communication and Distributed Systems, RWTH Aachen University
   Ahornstrasse 55

   Phone: +49 241 80 20 776

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