Host Identity Protocol                                              Heer
Internet-Draft                           Distributed Systems Group, RWTH
Intended status: Experimental                          Aachen University
Expires: March 27, May 12, 2011                                           Varjonen
                                      Helsinki Institute for Information
                                                      September 23,
                                                        November 8, 2010


                  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 HIP Host Identity Protocol (HIP) control
   packets.  This document only specifies the certificate parameter and
   the error signaling in case of a failed verification.  The use of
   certificates including how certificates are obtained, requested, and
   which actions are taken upon successful or failed verification are to
   be defined in the documents that use the certificate parameter.
   Additionally, this document specifies the representations of Host
   Identity Tags in X.509.v3 and SPKI certificates.

Requirements Language

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

Status of this Memo

   This Internet-Draft is submitted to IETF in full conformance with the
   provisions of BCP 78 and BCP 79.  This document may not be modified,
   and derivative works of it may not be created, except to format it
   for publication as an RFC or to translate it into languages other
   than English.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on March 27, May 12, 2011.

Copyright Notice

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

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   ( 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 BSD License.

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 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.

   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 but 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 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.  Only a single
   Cert group MAY span two subsequent packets.

   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     Describes     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 [RFC3280].  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 to and 4) are used as defined in [RFC4306]
   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 [RFC2255].  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
   [RFC1779].  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 and or subject alternative name extensions as
   defined in [RFC2459].  If only HIP information HIT of the host is presented as either
   the issuer or the subject the respective HIT is also MUST be placed into the
   respective entity's DNs DN's Common Name (CN) section in a colon
   delimited presentation format. 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 example illustrates a case examples illustrate how HITs are presented as issuer
   and subject in which the issuer DN and in the
   subject are both HIP enabled.

       Format: X.509.v3 extension alternative

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

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

       Format of X509v3 extensions:
           X509v3 Issuer Alternative Name:
               IP Address:HIT-OF-HOST Address:HIT-OF-ISSUER
           X509v3 Subject Alternative Name:
               IP Address:HIT-OF-HOST

           Issuer: CN=2001:14:6cf:fae7:bb79:bf78:7d64:c056
           Subject: CN=2001:14:6cf:fae7:bb79:bf78:7d64:c056 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:2001:14:6CF:FAE7:BB79:BF78:7D64:C056 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 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 in [RFC2459].  Revocation of SPKI certificates is handled as
   defined in Section 5 in [RFC2693].

6.  Error signaling

   If the Initiator does not send the certificate that the Responder
   requires the Responder may take actions (e.g. blocking 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 contains 4 octets, MAY contain n groups of 2 octets (n calculated
     from the NOTIFICATION parameter length), in order Cert group,
     Cert count, Cert ID, group and
     Cert type 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).

   It is not recommended NOT RECOMMENDED to use grouping or hash and URL encodings when
   HIP aware middleboxes are anticipated to be present on the
   communication path between peers because fetching remote certificates
   require the middlebox to buffer the packets and to request remote
   data.  This makes these devices prone to denial of service (DoS)
   attacks.  Moreover, middleboxes and responders that request remote
   certificates can be used as deflectors for distributed denial of
   service attacks.

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

   [RFC1779]  Kille, S., "A String Representation of Distinguished
              Names", RFC 1779, March 1995.

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

   [RFC2255]  Howes, T. and M. Smith, "The LDAP URL Format", RFC 2255,
              December 1997.

   [RFC2459]  Housley, R., Ford, W., Polk, T., and D. Solo, "Internet
              X.509 Public Key Infrastructure Certificate and CRL
              Profile", RFC 2459, January 1999.

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

   [RFC3280]  Housley, R., Polk, W., Ford, W., and D. Solo, "Internet
              X.509 Public Key Infrastructure Certificate and
              Certificate Revocation List (CRL) Profile", RFC 3280,
              April 2002.

   [RFC4306]  Kaufman, C., "Internet Key Exchange (IKEv2) Protocol",
              RFC 4306, December 2005.

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

   [RFC5952]  Kawamura, S. and M. Kawashima, "A Recommendation for IPv6
              Address Text Representation", RFC 5952, August 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 |uV7M1dl7OcJCPnlJrX8MvQ8SmE6wne5idnp7VfDMolestu
         (hash hit 2001:001e:d709:1980:5c6a:bb0c:7650:a027)
         (hash hit 2001:001c:5a14:26de:a07c:385b:de35:60e3)
       (not-before "2010-06-22_16:40:47")
       (not-after "2010-07-02_16:40:47")
       (hash sha1 |+UzjNn5+bXo3aMZQNGGtapKdlFAA|)

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 about DN usage.

   o  Revised text about Cert group usage.

   Changes from version 01 to 02:

   o  Revised the type numbers.

   o  Added a section about signaling.

   Changes from version 02 to 03:

   o  Revised text about CERT use 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.

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
   Metsaenneidonkuja 4
   Gustaf Haellstroemin katu 2b