Host Identity Protocol                                              Heer
Internet-Draft                           Distributed Systems Group, RWTH
Intended status: Informational Experimental                          Aachen University
Expires: October 30, 2010 March 27, 2011                                         Varjonen
                                      Helsinki Institute for Information
                                                          April 28,
                                                      September 23, 2010

                            HIP Certificates


   This document specifies a certificate parameter called CERT for the
   Host Identity Protocol (HIP).

   The CERT parameter is a container for X.509.v3 certificates and for
   Simple Public Key Infrastructure (SPKI) certificates.  It is used for
   carrying these certificates in 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 in 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].

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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] (HIP) [RFC5201] defines a new cryptographic
   namespace based on asymmetric cryptography.  Each host's  The identity of each
   host is derived from a public key, allowing hosts to digitally sign
   data with their private key.  This document specifies a the CERT parameter that
   parameter, which is used to transmit digital signatures certificates in HIP.  It
   fills the placeholder specified in Section 5.2 of [RFC5201].

2.  CERT Parameter

   The CERT parameter is a container for a certain types of digital
   certificates.  It may MAY either carry SPKI certificates or X.509.v3
   certificates.  It does not specify any certificate semantics.
   However, it defines some organizational supplementary parameters that help HIP hosts to
   transmit semantically grouped CERT parameters in a more systematic
   way.  The specific use of the CERT parameter may be covered 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 CERT it in the
   I1 packet is NOT RECOMMENDED. not recommended because it can increase the processing
   times of I1s, which can be problematic when processing storms of I1s.
   Each allowed HIP control packet may MAY contain multiple CERT parameters.  These
   parameters may MAY be related or unrelated.  Related certificates are
   managed in Cert groups.  A Cert group specifies a group of related
   CERT parameters that should 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 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 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 MUST
   be placed in ascending order, within a HIP control packet, according
   to their Cert group field.  Cert groups may MAY only span multiple
   packets if the Cert group does not fit the packet.  Only one a single
   Cert group may 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 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 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      |
             |        Hash of X.509.v3        |      5      |
             |          Hash of SPKI          |      6      |
             |      LDAP URL of X.509.v3      |      7      5      |
             |        LDAP URL of SPKI        |      8      6      |
             | Distinguished Name of X.509.v3 |      9      7      |
             |   Distinguished Name of SPKI   |      10      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 6) 4) are used as defined in [RFC4306]. [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 encoding (7 encodings (5 and 8) is 6) are used as defined in [RFC2255].  Using
   LDAP URL encoding results in smaller HIP control packets, packets but requires
   the receiver to retrieve the certificate or check a local cache
   against the URL.

   Distinguished name (DN) encoding (9 encodings (7 and 10) is 8) are used as defined in
   [RFC1779].  Using LDAP URL 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

   HITs need to be enclosed within the certificates, when

   When using X.509.v3 certificates to transmit information related to
   HIP hosts. 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 subject alternative name extensions as
   defined in [RFC2459].  If only HIP information is presented as either
   the issuer or the subject the HIT is also placed into the respective
   entity's DNs Common Name (CN) section in a colon delimited
   presentation format.  Inclusion of CN is not necessary if DN contains
   any other information.  It is RECOMMENDED to use the FQDN/NAI from
   the hosts HOST_ID parameter in the DN if one exists.  Full  The full HIs
   are presented in the public key entries of X.509.v3 certificates.

   As an example, in

   The following example illustrates a case where in which the issuer and the
   subject are both HIP enabled, the HITs are expressed as follows: enabled.

           Issuer: CN=hit-of-host
           Subject: CN=hit-of-host

           X509v3 extensions:
               X509v3 Issuer Alternative Name:
                   IP Address:HIT-OF-HOST
               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

           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

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

4.  SPKI Cert Object and Host Identities

   HITs need

   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 enclosed within configured to compute HITs and
   include them in the certificates, when 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.
   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 SPKI X.509.v3 certificates is handled as defined in Section 5.
   5 in [RFC2693] [RFC2459].  Revocation of X.509.v3 SPKI certificates is handled as
   defined in Section 5 in [RFC2459]. [RFC2693].

6.  Signaling

   HIP end-hosts and HIP-aware middleboxes need  Error signaling

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

   If the responder, verification of the need for a certificate or need for a chain
   of certificates.  They also need fails, a way to inform about failing verifier MAY signal
   this to
   meet required conditions.  HIP services [HIP.service] describes the
   signaling.  Signaling for provider of the requirements and failures certificate by sending a HIP NOTIFY
   message with
   certificates NOTIFICATION parameter error type INVALID_CERTIFICATE.

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

     CREDENTIALS_REQUIRED                      48

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

     INVALID_CERTIFICATE                       50

     Sent in Section 4.1 response to a failed verification of [HIP.service]. a certificate.
     Notification Data contains 4 octets, in order Cert group,
     Cert count, Cert ID, and Cert type 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].

   Cert Group CERT parameter has 8-bit unsigned integer field for different
   certificate types, for which IANA is to create and Cert ID namespaces maintain a new
   sub-registry entitled "HIP certificate types" under the "Host
   Identity Protocol (HIP) Parameters".  Initial values for the
   Certificate type registry are managed locally by each host
   that sends CERT parameters given in HIP control packets. 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, i.e. 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 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 of 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

              Heer, T., Wirtz, H., and S. Varjonen, "Service Identifiers
              for HIP", <draft-heer-hip-service-00.txt>.

   [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.

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 self-signed SPKI certificate of HIT 2001:14:6cf:
   fae7:bb79:bf78:7d64:c056. with encoded HITs.  The example
   has been indented for readability.

         (e #010001#)
         (n |n1CheoELqYRSkHYMQddub2TpILl+6H9wC/as6zFCZqOY43hsZgAjG0F
             gbK3S8=| |uV7M1dl7OcJCPnlJrX8MvQ8SmE6wne5idnp7VfDMolestu
         (hash hit 2001:0014:06cf:fae7:bb79:bf78:7d64:c056) 2001:001e:d709:1980:5c6a:bb0c:7650:a027)
         (hash hit 2001:0014:06cf:fae7:bb79:bf78:7d64:c056) 2001:001c:5a14:26de:a07c:385b:de35:60e3)
       (not-before "2008-07-12_22:11:07") "2010-06-22_16:40:47")
       (not-after "2008-07-22_22:11:07") "2010-07-02_16:40:47")
       (hash sha1 |kfElDhagiK0Bsqtj32Gq3t/1mxgA|)
        E42LmDskM9T5KQJoC/CH7871zfvojPnpkl2dUngOWv4q0r/wSJ0=| |+UzjNn5+bXo3aMZQNGGtapKdlFAA|)

Appendix B.  X.509.v3 certificate example

   This section shows a self-signed X.509.v3 certificate of HIT 2001:14:
   6cf:fae7:bb79:bf78:7d64:c056. with encoded HITs.

           Version: 3 (0x2)
           Serial Number: 0 (0x0)
           Signature Algorithm: sha1WithRSAEncryption
           Issuer: CN=2001:14:6cf:fae7:bb79:bf78:7d64:c056 CN=2001:1e:d709:1980:5c6a:bb0c:7650:a027
               Not Before: Jul 12 18:58:38 2008 Jun 22 13:39:32 2010 GMT
               Not After : Jul 22 18:58:38 2008  2 13:39:32 2010 GMT
           Subject: CN=2001:14:6cf:fae7:bb79:bf78:7d64:c056 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 Basic Constraints:
               X509v3 Issuer Alternative Name:
                   IP Address:2001:14:6CF:FAE7:BB79:BF78:7D64:C056 Address:2001:1E:D709:1980:5C6A:BB0C:7650:A027
               X509v3 Subject Alternative Name:
                   IP Address:2001:14:6CF:FAE7:BB79:BF78:7D64:C056 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

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

   Fax:   +35896949768