Skip to main content

Host Identity Protocol Certificates

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 8002.
Authors Tobias Heer , Samu Varjonen
Last updated 2018-12-20 (Latest revision 2016-07-06)
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd Gonzalo Camarillo
Shepherd write-up Show Last changed 2015-11-08
IESG IESG state Became RFC 8002 (Proposed Standard)
Action Holders
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Terry Manderson
Send notices to "Gonzalo Camarillo" <>
IANA IANA review state IANA OK - Actions Needed
IANA action state RFC-Ed-Ack
Host Identity Protocol                                           T. Heer
Internet-Draft                           Albstadt-Sigmaringen University
Obsoletes: 6253 (if approved)                                S. Varjonen
Updates: 7401 (if approved)                       University of Helsinki
Intended status: Standards Track                            July 6, 2016
Expires: January 7, 2017

                  Host Identity Protocol Certificates


   The Certificate (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).

   The concrete use cases 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 is left to the documents that use the CERT

   This document updates RFC7401 and obsoletes RFC6253.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at

   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."

   This Internet-Draft will expire on January 7, 2017.

Copyright Notice

Heer & Varjonen          Expires January 7, 2017                [Page 1]
Internet-Draft                  HIP CERT                       July 2016

   Copyright (c) 2016 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 Simplified BSD License.

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) [RFC7401] 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 [RFC7401], and thus, updates [RFC7401].

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.  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.

Heer & Varjonen          Expires January 7, 2017                [Page 2]
Internet-Draft                  HIP CERT                       July 2016

   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 each carrying one certificate.  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).  Ungrouped certificates exhibit a
   unique CERT group field and set the CERT count to 1.  CERT parameters
   with the same group number in the CERT 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 (variable length)   |

     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.

Heer & Varjonen          Expires January 7, 2017                [Page 3]
Internet-Draft                  HIP CERT                       July 2016

     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. Any added padding bytes MUST be zeroed by
                   the sender, and their values SHOULD NOT be checked by
                   the receiver.

   The certificates MUST use the algorithms defined in [RFC7401] as the
   signature and hash algorithms.

   The following certificate types are defined:

             |          CERT format           | Type number |
             |            Reserved            |      0      |
             |            X.509 v3            |      1      |
             |           Obsoleted            |      2      |
             |    Hash and URL of X.509 v3    |      3      |
             |           Obsoleted            |      4      |
             |      LDAP URL of X.509 v3      |      5      |
             |           Obsoleted            |      6      |
             | Distinguished Name of X.509 v3 |      7      |
             |           Obsoleted            |      8      |

   The next sections outline the use of Host Identity Tags (HITs) in
   X.509 v3.  X.509 v3 certificates and the handling procedures are
   defined in [RFC5280].  The wire format for X.509 v3 is the
   Distinguished Encoding Rules format as defined in [X.690].

   Hash and Uniform Resource Locator (URL) encoding (3) is used as
   defined in Section 3.6 of [RFC7296].  Using hash and URL encodings
   results in smaller HIP control packets than by including the
   certificate(s), but requires the receiver to resolve the URL or check
   a local cache against the hash.

   Lightweight Directory Access Protocol (LDAP) URL encoding (5) is 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) encoding (7) is 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.

Heer & Varjonen          Expires January 7, 2017                [Page 4]
Internet-Draft                  HIP CERT                       July 2016

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 [RFC7343].
   When the Host Identifier (HI) is used to sign the certificate, the
   respective HIT SHOULD be placed into 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 SHOULD be placed into the Subject
   Alternative Name (SAN) extension using the GeneralName form
   iPAddress, and the full HI is presented as the subject's 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:2001:24:6cf:fae7:bb79:bf78:7d64:c056
           X509v3 Subject Alternative Name:
               IP Address:2001:2c:5a14:26de:a07c:385b:de35:60e3

   Appendix A 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 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 SHOULD 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

Heer & Varjonen          Expires January 7, 2017                [Page 5]
Internet-Draft                  HIP CERT                       July 2016

4.  Revocation of Certificates

   Revocation of X.509 v3 certificates is handled as defined in
   Section 5 of [RFC5280] with two exceptions.  First, any HIP
   certificate serial number that appears on the CRL is treated as
   invalid regardless of the reason code.  Second, the certificateHold
   is not supported.

5.  Error Signaling

   If the Initiator does not send all the certificates 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 CERT group and CERT ID octet
     (in this order) of the CERT parameter that caused the

6.  IANA Considerations

   This document defines the CERT parameter for the Host Identity
   Protocol [RFC7401].  The CERT parameter type number (768) is defined
   in [RFC7401].

   The CERT parameter has an 8-bit unsigned integer field for different
   certificate types, for which IANA has created and maintains a sub-
   registry entitled "HIP certificate types" under the "Host Identity
   Protocol (HIP) Parameters".  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 Review.

Heer & Varjonen          Expires January 7, 2017                [Page 6]
Internet-Draft                  HIP CERT                       July 2016

   In Section 5, this document defines two types for the "NOTIFY message
   types" sub-registry under "Host Identity Protocol (HIP) Parameters".

   As this document obsoletes [RFC6253], references to [RFC6253] in IANA
   registries must be replaced by references to this document.  This
   document changes Certificate type registry in Section 2.

   The following updates to the "HIP Certificate Types" registry must be

      The references must be updated from [RFC6253] to this document.

      This document obsoleted the type numbers "2", "4", "6", "8" for
      the SPKI certificates.

7.  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, the sending of fragments in the
   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

   Although, CERT parameter is allowed in the first Initiator (I1)
   packet it is NOT RECOMMENDED because it can increase the processing
   times of I1s, which can be problematic when processing storms of I1s.
   Furthermore, Initiator has to take into consideration that the
   Responder can drop the CERT parameter in I1 without processing the

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

   Security considerations for X.509 v3 are discussed in [RFC5280].

8.  Differences from RFC 6253

   This section summarizes the technical changes made from [RFC6253].
   This section is informational, intended to help implementors of the
   previous protocol version.  If any text in this section contradicts
   text in other portions of this specification, the text found outside
   of this section should be considered normative.

   The following changes have been made.

Heer & Varjonen          Expires January 7, 2017                [Page 7]
Internet-Draft                  HIP CERT                       July 2016

   o  Support for Simple Public Key Infrastructure (SPKI) certificates
      has been removed.

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.

   [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

   [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.

   [RFC7296]  Kaufman, C., Hoffman, P., Nir, Y., Eronen, P., and T.
              Kivinen, "Internet Key Exchange Protocol Version 2
              (IKEv2)", STD 79, RFC 7296, DOI 10.17487/RFC7296, October
              2014, <>.

   [RFC7343]  Laganier, J. and F. Dupont, "An IPv6 Prefix for Overlay
              Routable Cryptographic Hash Identifiers Version 2
              (ORCHIDv2)", RFC 7343, DOI 10.17487/RFC7343, September
              2014, <>.

   [RFC7401]  Moskowitz, R., Heer, T., Jokela, P., and T. Henderson,
              "Host Identity Protocol Version 2 (HIPv2)", RFC 7401,
              April 2015.

   [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.

Heer & Varjonen          Expires January 7, 2017                [Page 8]
Internet-Draft                  HIP CERT                       July 2016

10.2.  Informative References

   [RFC6253]  Heer, T. and S. Varjonen, "Host Identity Protocol
              Certificates", RFC 6253, DOI 10.17487/RFC6253, May 2011,

Appendix A.  X.509 v3 certificate example

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

           Version: 3 (0x2)
           Serial Number: 12705268244493839545 (0xb0522e27291b2cb9)
       Signature Algorithm: sha256WithRSAEncryption
           Issuer: DC=Example, DC=com, CN=Example issuing host
               Not Before: Feb 25 11:28:29 2016 GMT
               Not After : Feb 24 11:28:29 2017 GMT
           Subject: DC=Example, DC=com, CN=Example issuing host
           Subject Public Key Info:
               Public Key Algorithm: rsaEncryption
                   Public-Key: (2048 bit)
                   Exponent: 65537 (0x10001)
           X509v3 extensions:
               X509v3 Subject Alternative Name:
                   IP Address:2001:27:DCFC:CB8:F885:D53F:4E63:48B7
               X509v3 Issuer Alternative Name:
                   IP Address:2001:2D:F878:64C1:67E3:9716:88BD:68E4

Heer & Varjonen          Expires January 7, 2017                [Page 9]
Internet-Draft                  HIP CERT                       July 2016

       Signature Algorithm: sha256WithRSAEncryption

   -----END CERTIFICATE-----

Appendix B.  Change log

   Contents of draft-ietf-hip-rfc6253-bis-00:

   o  RFC6253 was submitted as draft-RFC.

   Changes from version 01 to 02:

   o  Updated the references.

Heer & Varjonen          Expires January 7, 2017               [Page 10]
Internet-Draft                  HIP CERT                       July 2016

   Changes from version 02 to 03:

   o  Fixed the nits raised by the working group.

   Changes from version 03 to 04:

   o  Added "obsoletes RFC 6253".

   Changes from version 04 to 05:

   o  Updates to contact details.

   o  Correct updates and obsoletes headers.

   o  Removed the pre5378 disclaimer.

   o  Updated references.

   o  Removed the SPKI references from the document.

   Changes from version 05 to 06:

   o  Addressed the Int-Dir review comments from Korhonen.

   Changes from version 06 to 07:

   o  Addressed the GenArt, OPSdir, SecDir, and IANA comments.

   Changes from version 07 to 08:

   o  Addresses one editorial nit for CERT group numbers.

   Changes from version 08 to 09:

   o  Rewrote the IANA section.

Authors' Addresses

   Tobias Heer
   Albstadt-Sigmaringen University
   Poststr. 6
   72458 Albstadt


Heer & Varjonen          Expires January 7, 2017               [Page 11]
Internet-Draft                  HIP CERT                       July 2016

   Samu Varjonen
   University of Helsinki
   Gustaf Haellstroemin katu 2b
   00560 Helsinki


Heer & Varjonen          Expires January 7, 2017               [Page 12]