Host Identity Protocol                                              Heer
Internet-Draft                           Albstadt-Sigmaringen University
Obsoletes: 6253 (if approved)                                   Varjonen
Updates: 7401 (if approved)                       University of Helsinki
Intended status: Standards Track                        November 3, 2015
Expires: May 6, 2016

                  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 extends 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
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   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 May 6, 2016.

Copyright Notice

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   Copyright (c) 2015 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, extends [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.

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   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

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                   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 [RFC7401] as the
   signature and hash algorithms.

   The following certificate types are defined:

             |          Cert format           | Type number |
             |            Reserved            |      0      |
             |            X.509 v3            |      1      |
             |    Hash and URL of X.509 v3    |      2      |
             |      LDAP URL of X.509 v3      |      3      |
             | Distinguished Name of X.509 v3 |      4      |

   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) encodings (3 and 4) are 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 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 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 [RFC7343].

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   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

4.  Revocation of Certificates

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

5.  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 CERT parameter that caused the failure.

6.  IANA Considerations

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

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

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   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 in [RFC5280].

8.  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.

9.  References

9.1.  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),

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              Canonical Encoding Rules (CER) and Distinguished Encoding
              Rules (DER)", July 2002.

9.2.  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: 0 (0x0)
           Signature Algorithm: sha1WithRSAEncryption
           Issuer: CN=Example issuing host, DC=example, DC=com
               Not Before: Mar 11 09:01:39 2011 GMT
               Not After : Mar 21 09:01:39 2011 GMT
           Subject: 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:2001:23:8d83:41c5:dc9f:38ed:e742:7281
               X509v3 Subject Alternative Name:
                   IP Address:2001:2c:6e02:d3e0:9b90:8417:673e:99db
       Signature Algorithm: sha1WithRSAEncryption

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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.

   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.

Authors' Addresses

   Tobias Heer
   Albstadt-Sigmaringen University
   Poststr. 6
   72458 Albstadt


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   Samu Varjonen
   University of Helsinki
   Gustaf Haellstroemin katu 2b


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