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Versions: 00 01 02 03 04 05 06 07 08 09 10 11 12 RFC 4945

pki4ipsec                                                      B. Korver
Internet-Draft                                   Network Resonance, Inc.
Expires: October 14, 2006                                 April 12, 2006


 The Internet IP Security PKI Profile of IKEv1/ISAKMP, IKEv2, and PKIX
                draft-ietf-pki4ipsec-ikecert-profile-10

Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire on October 14, 2006.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   IKE and PKIX certificate profile both provide frameworks that must be
   profiled for use in a given application.  This document provides a
   profile of IKE and PKIX that defines the requirements for using PKI
   technology in the context of IKE/IPsec.  The document complements
   protocol specifications such as IKEv1 and IKEv2, which assume the
   existence of public key certificates and related keying materials,
   but which do not address PKI issues explicitly.  This document
   addresses those issues.




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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Terms and Definitions  . . . . . . . . . . . . . . . . . . . .  4
   3.  Profile of IKEv1/ISAKMP and IKEv2  . . . . . . . . . . . . . .  5
     3.1.  Identification Payload . . . . . . . . . . . . . . . . . .  5
       3.1.1.  ID_IPV4_ADDR and ID_IPV6_ADDR  . . . . . . . . . . . .  7
       3.1.2.  ID_FQDN  . . . . . . . . . . . . . . . . . . . . . . .  9
       3.1.3.  ID_USER_FQDN . . . . . . . . . . . . . . . . . . . . . 10
       3.1.4.  ID_IPV4_ADDR_SUBNET, ID_IPV6_ADDR_SUBNET,
               ID_IPV4_ADDR_RANGE, ID_IPV6_ADDR_RANGE . . . . . . . . 11
       3.1.5.  ID_DER_ASN1_DN . . . . . . . . . . . . . . . . . . . . 11
       3.1.6.  ID_DER_ASN1_GN . . . . . . . . . . . . . . . . . . . . 12
       3.1.7.  ID_KEY_ID  . . . . . . . . . . . . . . . . . . . . . . 12
       3.1.8.  Selecting an Identity from a Certificate . . . . . . . 12
       3.1.9.  Subject for DN Only  . . . . . . . . . . . . . . . . . 12
       3.1.10. Binding Identity to Policy . . . . . . . . . . . . . . 12
     3.2.  Certificate Request Payload  . . . . . . . . . . . . . . . 13
       3.2.1.  Certificate Type . . . . . . . . . . . . . . . . . . . 14
       3.2.2.  X.509 Certificate - Signature  . . . . . . . . . . . . 14
       3.2.3.  Revocation Lists (CRL and ARL) . . . . . . . . . . . . 14
       3.2.4.  PKCS #7 wrapped X.509 certificate  . . . . . . . . . . 15
       3.2.5.  IKEv2's Hash and URL of X.509 certificate  . . . . . . 15
       3.2.6.  Location of Certificate Payloads . . . . . . . . . . . 15
       3.2.7.  Presence or Absence of Certificate Request Payloads  . 15
       3.2.8.  Certificate Requests . . . . . . . . . . . . . . . . . 16
       3.2.9.  Robustness . . . . . . . . . . . . . . . . . . . . . . 18
       3.2.10. Optimizations  . . . . . . . . . . . . . . . . . . . . 18
     3.3.  Certificate Payload  . . . . . . . . . . . . . . . . . . . 19
       3.3.1.  Certificate Type . . . . . . . . . . . . . . . . . . . 20
       3.3.2.  X.509 Certificate - Signature  . . . . . . . . . . . . 20
       3.3.3.  Revocation Lists (CRL and ARL) . . . . . . . . . . . . 21
       3.3.4.  IKEv2's Hash and URL of X.509 Certificate  . . . . . . 21
       3.3.5.  PKCS #7 wrapped X.509 certificate  . . . . . . . . . . 21
       3.3.6.  Location of Certificate Payloads . . . . . . . . . . . 21
       3.3.7.  Certificate Payloads Not Mandatory . . . . . . . . . . 22
       3.3.8.  Response to Multiple Certification Authority
               Proposals  . . . . . . . . . . . . . . . . . . . . . . 22
       3.3.9.  Using Local Keying Materials . . . . . . . . . . . . . 22
       3.3.10. Multiple End-Entity Certificates . . . . . . . . . . . 22
       3.3.11. Robustness . . . . . . . . . . . . . . . . . . . . . . 23
       3.3.12. Optimizations  . . . . . . . . . . . . . . . . . . . . 24
   4.  Certificate Profile  . . . . . . . . . . . . . . . . . . . . . 24
     4.1.  X.509 Certificates . . . . . . . . . . . . . . . . . . . . 24
       4.1.1.  Versions . . . . . . . . . . . . . . . . . . . . . . . 25
       4.1.2.  Subject  . . . . . . . . . . . . . . . . . . . . . . . 25
       4.1.3.  X.509 Certificate Extensions . . . . . . . . . . . . . 26
     4.2.  X.509 Certificate Revocation Lists . . . . . . . . . . . . 31



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       4.2.1.  Multiple Sources of Certificate Revocation
               Information  . . . . . . . . . . . . . . . . . . . . . 32
       4.2.2.  X.509 Certificate Revocation List Extensions . . . . . 32
     4.3.  Strength of Signature Hashing Algorithms . . . . . . . . . 33
   5.  Configuration Data Exchange Conventions  . . . . . . . . . . . 34
     5.1.  Certificates . . . . . . . . . . . . . . . . . . . . . . . 34
     5.2.  CRLs and ARLs  . . . . . . . . . . . . . . . . . . . . . . 35
     5.3.  Public Keys  . . . . . . . . . . . . . . . . . . . . . . . 35
     5.4.  PKCS#10 Certificate Signing Requests . . . . . . . . . . . 35
   6.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 35
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 35
     7.1.  Certificate Request Payload  . . . . . . . . . . . . . . . 36
     7.2.  IKEv1 Main Mode  . . . . . . . . . . . . . . . . . . . . . 36
     7.3.  Disabling Certificate Checks . . . . . . . . . . . . . . . 36
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 36
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 36
     9.1.  Normative References . . . . . . . . . . . . . . . . . . . 36
     9.2.  Informative References . . . . . . . . . . . . . . . . . . 37
   Appendix A.  The Possible Dangers of Delta CRLs  . . . . . . . . . 38
   Appendix B.  More on Empty CERTREQs  . . . . . . . . . . . . . . . 38
   Appendix C.  Change History  . . . . . . . . . . . . . . . . . . . 40
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 51
   Intellectual Property and Copyright Statements . . . . . . . . . . 52




























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1.  Introduction

   IKE [1], ISAKMP [2] and IKEv2 [3] provide a secure key exchange
   mechanism for use with IPsec [4].  In many cases the peers
   authenticate using digital certificates as specified in PKIX [5].
   Unfortunately, the combination of these standards leads to an
   underspecified set of requirements for the use of certificates in the
   context of IPsec.

   ISAKMP references the PKIX certificate profile, but in many cases
   merely specifies the contents of various messages without specifying
   their syntax or semantics.  Meanwhile, the PKIX certificate profile
   provides a large set of certificate mechanisms which are generally
   applicable for Internet protocols, but little specific guidance for
   IPsec.  Given the numerous underspecified choices, interoperability
   is hampered if all implementers do not make similar choices, or at
   least fail to account for implementations which have chosen
   differently.

   This profile of the IKE and PKIX frameworks is intended to provide an
   agreed-upon standard for using PKI technology in the context of IPsec
   by profiling the PKIX framework for use with IKE and IPsec, and by
   documenting the contents of the relevant IKE payloads and further
   specifying their semantics.

   In addition to providing a profile of IKE and PKIX, this document
   attempts to incorporate lessons learned from recent experience with
   both implementation and deployment, as well as the current state of
   related protocols and technologies.

   Material from ISAKMP, IKEv1, IKEv2, or PKIX is not repeated here, and
   readers of this document are assumed to have read and understood
   those documents.  The requirements and security aspects of those
   documents are fully relevant to this document as well.

   This document is organized as follows.  Section 2 defines special
   terminology used in the rest of this document, Section 3 provides the
   profile of IKEv1/ISAKMP and IKEv2, and Section 4 provides the profile
   of PKIX.  Section 5 covers conventions for the out-of-band exchange
   of keying materials for configuration purposes.


2.  Terms and Definitions

   Except for those terms which are defined immediately below, all terms
   used in this document are defined in either the PKIX [5], ISAKMP [2],
   IKEv1 [1], IKEv2 [3], or DOI [6] documents.




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   o  Peer source address: The source address in packets from a peer.
      This address may be different from any addresses asserted as the
      "identity" of the peer.
   o  FQDN: Fully qualified domain name.
   o  ID_USER_FQDN: IKEv2 renamed ID_USER_FQDN to ID_RFC822_ADDR.  Both
      are referred to as ID_USER_FQDN in this document.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC-2119 [7].


3.  Profile of IKEv1/ISAKMP and IKEv2

3.1.  Identification Payload

   The Identification (ID) Payload indicates the identity claimed by the
   sender.  The recipient can then use the ID as a lookup key for policy
   and for certificate lookup in whatever certificate store or directory
   that it has available.  Our primary concern in this section is to
   profile the ID payload so that it can be safely used to generate or
   lookup policy.  IKE mandates the use of the ID payload in Phase 1.

   The DOI [6] defines the 11 types of Identification Data that can be
   used and specifies the syntax for these types.  These are discussed
   below in detail.

   The ID payload requirements in this document cover only the portion
   of the explicit policy checks that deal with the Identification
   Payload specifically.  For instance, in the case where ID does not
   contain an IP address, checks such as verifying that the peer source
   address is permitted by the relevant policy are not addressed here as
   they are out of the scope of this document.

   Implementations SHOULD populate ID with identity information that is
   contained within the end-entity certificate (This SHOULD does not
   contradict text in IKEv2 [3] Section 3.5 that implies a looser
   binding between these two).  Populating ID with identity information
   from the end-entity certificate enables recipients to use ID as a
   lookup key to find the peer end-entity certificate.  The only case
   where implementations MAY populate ID with information that is not
   contained in the end-entity certificate is when ID contains the peer
   source address (a single address, not a subnet or range).

   Because implementations may use ID as a lookup key to determine which
   policy to use, all implementations MUST be especially careful to
   verify the truthfulness of the contents by verifying that they
   correspond to some keying material demonstrably held by the peer.



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   Failure to do so may result in the use of an inappropriate or
   insecure policy.  The following sections describe the methods for
   performing this binding.

   The following table summarizes the binding of the Identification
   Payload to the contents of end-entity certificates and of identity
   information to policy.  Each ID type is covered more thoroughly in
   the following sections.

   ID type  | Support  | Correspond  | Cert     | SPD lookup
            | for send | PKIX Attrib | matching | rules
   -------------------------------------------------------------------
            |          |             |          |
   IP*_ADDR | MUST [a] | SubjAltName | MUST [b] | [c], [d]
            |          | iPAddress   |          |
            |          |             |          |
   FQDN     | MUST [a] | SubjAltName | MUST [b] | [c], [d]
            |          | dNSName     |          |
            |          |             |          |
   USER_FQDN| MUST [a] | SubjAltName | MUST [b] | [c], [d]
            |          | rfc822Name  |          |
            |          |             |          |
   IP range | MUST NOT | n/a         | n/a      | n/a
            |          |             |          |
   DN       | MUST [a] | Entire      | MUST [b] | MUST support lookup
            |          | Subject,    |          | on any combination
            |          | bitwise     |          | of C, CN, O, or OU
            |          | compare     |          |
            |          |             |          |
   GN       | MUST NOT | n/a         | n/a      | n/a
            |          |             |          |
   KEY_ID   | MUST NOT | n/a         | n/a      | n/a
            |          |             |          |


   [a] = Implementation MUST have the configuration option to send this
   ID type in the ID payload.  Whether or not the ID type is used is a
   matter of local configuration.

   [b] = The ID in the ID payload MUST match the contents of the
   corresponding field (listed) in the certificate exactly, with no
   other lookup.  The matched ID MAY be used for SPD lookup, but is not
   required to be used for this.  See RFC 4301 [10], section 4.4.3.2 for
   more details.

   [c] = At a minimum, Implementation MUST be capable of being
   configured to perform exact matching of the ID payload contents to an
   entry in the local SPD.



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   [d] = In addition, the implementation MAY also be configurable to
   perform substring or wildcard matches of ID payload contents to
   entries in the local SPD.  (More on this in Section 3.1.5).

   When sending an IPV4_ADDR, IPV6_ADDR, FQDN, or USER_FQDN,
   implementations MUST be able to be configured to send the same string
   as appears in the corresponding SubjectAltName extension.  This
   document RECOMMENDS that deployers use this configuration option.
   All these ID types are treated the same: as strings that can be
   compared easily and quickly to a corresponding string in an explicit
   value in the certificate.  Of these types, FQDN and USER_FQDN are
   RECOMMENDED over IP addresses (see discussion in Section 3.1.1).

   When sending a DN as ID, implementations MUST send the entire DN in
   ID.  Also, implementations MUST support at least the C, CN, O, and OU
   attributes for SPD matching.  See Section 3.1.5 for more details
   about DN, including SPD matching.

   Recipients MUST be able to perform SPD matching on the exact contents
   of the ID, and this SHOULD be the default setting.  In addition,
   implementations MAY use substrings or wildcards in local policy
   configuration to do the SPD matching against the ID contents.  In
   other words, implementations MUST be able to do exact matches of ID
   to SPD, but MAY also be configurable to do substring or wildcard
   matches of ID to SPD.

   IKEv2 adds an optional IDr payload in the second exchange that the
   initiator may send to the responder in order to specify which of the
   responder's multiple identities should be used.  The responder MAY
   choose to send an IDr in the 3rd exchange that differs in type or
   content from the initiator-generated IDr.  The initiator MUST be able
   to receive a responder-generated IDr that is a different type from
   the one the initiator generated.

3.1.1.  ID_IPV4_ADDR and ID_IPV6_ADDR

   Implementations MUST support either the ID_IPV4_ADDR or ID_IPV6_ADDR
   ID type, depending on whether the implementation supports IPv4, IPv6
   or both.  These addresses MUST be encoded in "network byte order," as
   specified in IP [8]: The least significant bit (LSB) of each octet is
   the LSB of the corresponding byte in the network address.  For the
   ID_IPV4_ADDR type, the payload MUST contain exactly four octets [8].
   For the ID_IPV6_ADDR type, the payload MUST contain exactly sixteen
   octets [11].

   Implementations SHOULD NOT populate ID payload with IP addresses due
   to interoperability issues such as problems with NAT traversal, and
   problems with IP verification behavior.



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   Deployments may only want to consider using the IP address as ID if
   all of the following are true:

   o  the peer's IP address is static, not dynamically changing
   o  the peer is NOT behind a NAT'ing device
   o  the administrator intends the implementation to verify that the
      peer source address matches the IP address in the ID received, and
      that in the iPAddress field in the peer certificate's
      SubjectAltName extension.

   Implementations MUST be capable of verifying that the IP address
   presented in ID matches via bitwise comparison the IP address present
   in the certificate's iPAddress field of the SubjectAltName extension.
   Implementations MUST perform this verification by default.  When
   comparing the contents of ID with the iPAddress field in the
   SubjectAltName extension for equality, binary comparison MUST be
   performed.  Note that certificates may contain multiple address
   identity types in which case at least one must match the source IP.
   If the default is enabled, then a mismatch between the two addresses
   MUST be treated as an error and security association setup MUST be
   aborted.  This event SHOULD be auditable.  Implementations MAY
   provide a configuration option to (i.e. local policy configuration
   can enable) skip that verification step, but that option MUST be off
   by default.  We include the "option-to-skip-validation" in order to
   permit better interoperability, as today implementations vary greatly
   in how they behave on this topic.

   In addition, implementations MUST be capable of verifying that the
   address contained in the ID is the same as the peer source address,
   contained in the outer most IP header.  If ID is one of the IP
   address types, then implementations MUST perform this verification by
   default.  If this default is enabled, then a mismatch MUST be treated
   as an error and security association setup MUST be aborted.  This
   event SHOULD be auditable.  Implementations MAY provide a
   configuration option to (i.e. local policy configuration can enable)
   skip that verification step, but that option MUST be off by default.
   We include the "option-to-skip-validation" in order to permit better
   interoperability, as today implementations vary greatly in how they
   behave on the topic of verification of source IP.

   If the default for both the verifications above are enabled, then, by
   transitive property, the implementation will also be verifying that
   the peer source IP address matches via a bitwise comparison the
   contents of the iPAddress field in the SubjectAltName extension in
   the certificate.  In addition, implementations MAY allow
   administrators to configure a local policy that explicitly requires
   that the peer source IP address match via a bitwise comparison the
   contents of the iPAddress field in the SubjectAltName extension in



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   the certificate.  Implementations SHOULD allow administrators to
   configure a local policy that skips this validation check.

   Implementations MAY support substring, wildcard, or regular
   expression matching of the contents of ID to lookup policy in the
   SPD, and such would be a matter of local security policy
   configuration.

   Implementations MAY use the IP address found in the header of packets
   received from the peer to lookup the policy, but such implementations
   MUST still perform verification of the ID payload.  Although packet
   IP addresses are inherently untrustworthy and must therefore be
   independently verified, it is often useful to use the apparent IP
   address of the peer to locate a general class of policies that will
   be used until the mandatory identity-based policy lookup can be
   performed.

   For instance, if the IP address of the peer is unrecognized, a VPN
   gateway device might load a general "road warrior" policy that
   specifies a particular CA that is trusted to issue certificates which
   contain a valid rfc822Name which can be used by that implementation
   to perform authorization based on access control lists (ACLs) after
   the peer's certificate has been validated.  The rfc822Name can then
   be used to determine the policy that provides specific authorization
   to access resources (such as IP addresses, ports, and so forth).

   As another example, if the IP address of the peer is recognized to be
   a known peer VPN endpoint, policy may be determined using that
   address, but until the identity (address) is validated by validating
   the peer certificate, the policy MUST NOT be used to authorize any
   IPsec traffic.

3.1.2.  ID_FQDN

   Implementations MUST support the ID_FQDN ID type, generally to
   support host-based access control lists for hosts without fixed IP
   addresses.  However, implementations SHOULD NOT use the DNS to map
   the FQDN to IP addresses for input into any policy decisions, unless
   that mapping is known to be secure, for example if DNSSEC [12] were
   employed for that FQDN.

   If ID contains an ID_FQDN, implementations MUST be capable of
   verifying that the identity contained in the ID payload matches
   identity information contained in the peer end-entity certificate, in
   the dNSName field in the SubjectAltName extension.  Implementations
   MUST perform this verification by default.  When comparing the
   contents of ID with the dNSName field in the SubjectAltName extension
   for equality, caseless string comparison MUST be performed.  Note



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   that caseless string comparison works on internationalized domain
   names (IDNs) as well (See IDN [13]).  Substring, wildcard, or regular
   expression matching MUST NOT be performed for this comparison.  If
   this default is enabled, then a mismatch MUST be treated as an error
   and security association setup MUST be aborted.  This event SHOULD be
   auditable.  Implementations MAY provide a configuration option to
   (i.e. local policy configuration can enable) skip that verification
   step, but that option MUST be off by default.  We include the
   "option-to-skip-validation" in order to permit better
   interoperability, as today implementations vary greatly in how they
   behave on this topic.

   Implementations MAY support substring, wildcard, or regular
   expression matching of the contents of ID to lookup policy in the
   SPD, and such would be a matter of local security policy
   configuration.

3.1.3.  ID_USER_FQDN

   Implementations MUST support the ID_USER_FQDN ID type, generally to
   support user-based access control lists for users without fixed IP
   addresses.  However, implementations SHOULD NOT use the DNS to map
   the FQDN portion to IP addresses for input into any policy decisions,
   unless that mapping is known to be secure, for example if DNSSEC [12]
   were employed for that FQDN.

   Implementations MUST be capable of verifying that the identity
   contained in the ID payload matches identity information contained in
   the peer end-entity certificate, in the rfc822Name field in the
   SubjectAltName extension.  Implementations MUST perform this
   verification by default.  When comparing the contents of ID with the
   rfc822Name field in the SubjectAltName extension for equality,
   caseless string comparison MUST be performed.  Note that caseless
   string comparison works on internationalized domain names (IDNs) as
   well (See IDN [13]).  Substring, wildcard, or regular expression
   matching MUST NOT be performed for this comparison.  If this default
   is enabled, then a mismatch MUST be treated as an error and security
   association setup MUST be aborted.  This event SHOULD be auditable.
   Implementations MAY provide a configuration option to (i.e. local
   policy configuration can enable) skip that verification step, but
   that option MUST be off by default.  We include the "option-to-skip-
   validation" in order to permit better interoperability, as today
   implementations vary greatly in how they behave on this topic.

   Implementations MAY support substring, wildcard, or regular
   expression matching of the contents of ID to lookup policy in the
   SPD, and such would be a matter of local security policy
   configuration.



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3.1.4.  ID_IPV4_ADDR_SUBNET, ID_IPV6_ADDR_SUBNET, ID_IPV4_ADDR_RANGE,
        ID_IPV6_ADDR_RANGE

   Note that RFC 3779 [14] defines blocks of addresses using the
   certificate extension identified by:

            id-pe-ipAddrBlock OBJECT IDENTIFIER ::= { id-pe 7 }

   although use of this extension in IKE is considered experimental at
   this time.

3.1.5.  ID_DER_ASN1_DN

   Implementations MUST support receiving the ID_DER_ASN1_DN ID type.
   Implementations MUST be capable of generating this type, and the
   decision to do so will be a matter of local security policy
   configuration.  When generating this type, implementations MUST
   populate the contents of ID with the Subject field from the end-
   entity certificate, and MUST do so such that a binary comparison of
   the two will succeed.  If there is not a match, this MUST be treated
   as an error and security association setup MUST be aborted.  This
   event SHOULD be auditable.  Note, if the certificate was erroneously
   created such that the encoding of the Subject DN varies from the
   constraints set by DER, that non-conformant DN MUST be used to
   populate the ID payload: in other words, implementations MUST NOT re-
   encode the DN for the purposes of making it DER if it does not appear
   in the certificate as DER.

   Implementations MUST NOT populate ID with the Subject from the end-
   entity certificate if it is empty, even though an empty certificate
   Subject is explicitly allowed in the "Subject" section of the PKIX
   certificate profile.

   Regarding SPD matching, implementations MUST be able to perform
   matching based on a bitwise comparison of the entire DN in ID to its
   entry in the SPD.  However, operational experience has shown that
   using the entire DN in local configuration is difficult, especially
   in large scale deployments.  Therefore, implementations also MUST be
   able to perform SPD matches of any combination of one or more of the
   C, CN, O, OU attributes within Subject DN in the ID to the same in
   the SPD.  Implementations MAY support matching using additional DN
   attributes in any combination, although interoperability is far from
   certain and dubious.  Implementations MAY also support performing
   substring, wildcard, or regular expression matches for any of its
   supported DN attributes from ID, in any combination, to the SPD.
   Such flexibility allows deployers to create one SPD entry on the
   gateway for an entire department of a company (e.g.  O=Foobar Inc.,
   OU=Engineering) while still allowing them to draw out other details



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   from the DN (e.g.  CN=John Doe) for auditing purposes.  All the above
   is a matter of local implementation and local policy definition and
   enforcement capability, not bits on the wire, but will have a great
   impact on interoperability.

3.1.6.  ID_DER_ASN1_GN

   Implementations MUST NOT generate this type.

3.1.7.  ID_KEY_ID

   The ID_KEY_ID type used to specify pre-shared keys and thus is out of
   scope.

3.1.8.  Selecting an Identity from a Certificate

   Implementations MUST support certificates that contain more than a
   single identity, such as when the Subject field and the
   SubjectAltName extension are both populated, or the SubjectAltName
   extension contains multiple identities irrespective of whether the
   Subject is empty or not.  In many cases a certificate will contain an
   identity such as an IP address in the SubjectAltName extension in
   addition to a non-empty Subject.

   Implementations SHOULD populate ID with whichever identity is likely
   to be named in the peer's policy.  In practice, this generally means
   FQDN, or USER_FQDN, but this information may also be available to the
   administrator through some out-of-band means.  In the absence of such
   out-of-band configuration information, the identity with which an
   implementation chooses to populate the ID payload is a local matter.

3.1.9.  Subject for DN Only

   If an FQDN is intended to be processed as an identity for the
   purposes ID matching, it MUST be placed in the dNSName field of the
   SubjectAltName extension.  Implementations MUST NOT populate the
   Subject with an FQDN in place of populating the dNSName field of the
   SubjectAltName extension.

   While nothing prevents an FQDN, USER_FQDN, or IP address information
   from appearing somewhere in the Subject contents, such entries MUST
   NOT be interpreted as identity information for the purposes of
   matching with ID or for policy lookup.

3.1.10.  Binding Identity to Policy

   In the presence of certificates that contain multiple identities,
   implementations MUST select the most appropriate identity from the



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   certificate and populate the ID with that.  The recipient MUST use
   the identity sent as a first key when selecting the policy.  The
   recipient MUST also use the most specific policy from that database
   if there are overlapping policies caused by wildcards (or the
   implementation can de-correlate the policy database so there will not
   be overlapping entries, or it can also forbid creation of overlapping
   policies and leave the de-correlation process to the administrator,
   but as this moves the problem to the administrator it is NOT
   RECOMMENDED).

   For example, imagine that an implementation is configured with a
   certificate that contains both a non-empty Subject and a dNSName.
   The sender's policy may specify which of those to use, and it
   indicates the policy to the other end by sending that ID.  If the
   recipient has both a specific policy for the dNSName for this host
   and generic wildcard rule for some attributes present in the Subject
   field, it will match a different policy depending which ID is sent.
   As the sender knows why it wanted to connect the peer, it also knows
   what identity it should use to match the policy it needs to the
   operation it tries to perform; it is the only party who can select
   the ID adequately.

   In the event the policy cannot be found in the recipient's SPD using
   the ID sent, then the recipient MAY use the other identities in the
   certificate when attempting to match a suitable policy.  For example,
   say the certificate contains non-empty Subject field, a dNSName and
   an iPAddress.  If an iPAddress is sent in ID but no specific entry
   exists for the address in the policy database, the recipient MAY
   search in the policy database based on the Subject or the dNSName
   contained in the certificate.

   The Peer Authorization Database (PAD) as described in RFC 4301 [10]
   provides a more formal model for the binding of identity to policy in
   addition to providing services that deal more specifically with the
   details of policy enforcement, which are generally out of scope of
   this document.  The PAD is intended to provide a link between the SPD
   and the security association management in protocols such as IKE.
   See RFC 4301 [10], section 4.4.3 for more details.

3.2.  Certificate Request Payload

   The Certificate Request (CERTREQ) Payload allows an implementation to
   request that a peer provide some set of certificates or certificate
   revocation lists (CRLs).  It is not clear from ISAKMP exactly how
   that set should be specified or how the peer should respond.  We
   describe the semantics on both sides.





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3.2.1.  Certificate Type

   The Certificate Type field identifies to the peer the type of
   certificate keying materials that are desired.  ISAKMP defines 10
   types of Certificate Data that can be requested and specifies the
   syntax for these types, and IKEv2 specifies 3 additional types.  For
   the purposes of this document, only the following types are relevant:

   o  X.509 Certificate - Signature
   o  Revocation Lists (CRL and ARL)
   o  PKCS #7 wrapped X.509 certificate
   o  IKEv2's Hash and URL of X.509 certificate

   The use of the other types are out of the scope of this document:

   o  X.509 Certificate - Key Exchange
   o  PGP Certificate
   o  DNS Signed Key
   o  Kerberos Tokens
   o  SPKI Certificate
   o  X.509 Certificate Attribute
   o  IKEv2's Raw RSA Key
   o  IKEv2's Hash and URL of X.509 bundle

3.2.2.  X.509 Certificate - Signature

   This type requests that the end-entity certificate be a certificate
   used for signing.

3.2.3.  Revocation Lists (CRL and ARL)

   ISAKMP and IKEv2 do not support Certificate Payload sizes over
   approximately 64K, which is too small for many CRLs.  Therefore, the
   acquisition of revocation material is to be dealt with out-of-band of
   IKE.  For this and other reasons, implementations SHOULD NOT generate
   CERTREQs where the Certificate Type is "Certificate Revocation List
   (CRL)" or "Authority Revocation List (ARL)".  Implementations that do
   generate such CERTREQs MUST NOT require the recipient to respond with
   a CRL or ARL, and MUST NOT fail when not receiving any.  Upon receipt
   of such a CERTREQ, implementations MAY ignore the request.

   In lieu of exchanging revocation lists in-band, a pointer to
   revocation checking SHOULD be listed in either the
   CRLDistributionPoints (CDP) or the AuthorityInfoAccess (AIA)
   certificate extensions (see Section 4 for details).  Unless other
   methods for obtaining revocation information are available,
   implementations SHOULD be able to process these attributes, and from
   them be able to identify cached revocation material, or retrieve the



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   relevant revocation material from a URL, for validation processing.
   In addition, implementations MUST have the ability to configure
   validation checking information for each certification authority.
   Regardless of the method (CDP, AIA, or static configuration), the
   acquisition of revocation material SHOULD occur out-of-band of IKE.

3.2.4.  PKCS #7 wrapped X.509 certificate

   This ID type defines a particular encoding (not a particular
   certificate type), some current implementations may ignore CERTREQs
   they receive which contain this ID type, and the editors are unaware
   of any implementations that generate such CERTREQ messages.
   Therefore, the use of this type is deprecated.  Implementations
   SHOULD NOT require CERTREQs that contain this Certificate Type.
   Implementations which receive CERTREQs which contain this ID type MAY
   treat such payloads as synonymous with "X.509 Certificate -
   Signature".

3.2.5.  IKEv2's Hash and URL of X.509 certificate

   This ID type defines a request for the peer to send a hash and URL of
   its X.509 certificate, instead of the actual certificate itself.
   This is a particularly useful mechanism when the peer is a device
   with little memory and lower bandwidth, e.g. a mobile handset or
   consumer electronics device.

   If the IKEv2 implementation supports URL lookups, and prefers such a
   URL to receiving actual certificates, then the implementation will
   want to send a notify of type HTTP_CERT_LOOKUP_SUPPORTED.  From IKEv2
   [3], section 3.10.1, "This notification MAY be included in any
   message that can include a CERTREQ payload and indicates that the
   sender is capable of looking up certificates based on an HTTP-based
   URL (and hence presumably would prefer to receive certificate
   specifications in that format)."  If an HTTP_CERT_LOOKUP_SUPPORTED
   notification is sent the sender MUST support the http scheme.  See
   Section 3.3.4 for more discussion of HTTP_CERT_LOOKUP_SUPPORTED.

3.2.6.  Location of Certificate Payloads

   In IKEv1 Main Mode, the CERTREQ payload MUST be in messages 4 and 5.
   In IKEv2, the CERTREQ payload must be in messages 2 and 3.  Note that
   in IKEv2, it is possible to have one side authenticating with
   certificates while the other side authenticates with preshared keys.

3.2.7.  Presence or Absence of Certificate Request Payloads

   When in-band exchange of certificate keying materials is desired,
   implementations MUST inform the peer of this by sending at least one



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   CERTREQ.  In other words, an implementation which does not send any
   CERTREQs during an exchange SHOULD NOT expect to receive any CERT
   payloads.

3.2.8.  Certificate Requests

3.2.8.1.  Specifying Certification Authorities

   When requesting in-band exchange of keying materials, implementations
   SHOULD generate CERTREQs for every peer trust anchor that local
   policy explicitly deems trusted during a given exchange.  For IKEv1,
   implementations SHOULD populate the Certification Authority field
   with the Subject field of the trust anchor, populated such that
   binary comparison of the Subject and the Certification Authority will
   succeed.  For IKEv2, implementations MUST populate the Certification
   Authority field as specified in IKEv2 [3].

   Upon receipt of a CERTREQ, implementations MUST respond by sending at
   least the end-entity certificate corresponding to the Certification
   Authority listed in the CERTREQ unless local security policy
   configuration specifies that keying materials must be exchanged out-
   of-band.  Implementations MAY send certificates other than the end-
   entity certificate (see Section 3.3 for discussion).

   Note, in the case where multiple end-entity certificates may be
   available which chain to different trust anchors, implementations
   SHOULD resort to local heuristics to determine which trust anchor is
   most appropriate to use for generating the CERTREQ.  Such heuristics
   are out of the scope of this document.

3.2.8.2.  Empty Certification Authority Field

   Implementations SHOULD generate CERTREQs where the Certificate Type
   is "X.509 Certificate - Signature" and where a the Certification
   Authority field is not empty.  However, implementations MAY generate
   CERTREQs with an empty Certification Authority field under special
   conditions.  Although PKIX prohibits certificates with an empty
   Issuer field, there does exist a use case where doing so is
   appropriate, and carries special meaning in the IKE context.  This
   has become a convention within the IKE interoperability tests and
   usage space, and so its use is specified, explained here for the sake
   of interoperability.

   USE CASE: Consider the rare case where you have a gateway with
   multiple policies for a large number of IKE peers: some of these
   peers are business partners, some are remote access employees, some
   are teleworkers, some are branch offices, and/or the gateway may be
   simultaneously serving many customers (e.g.  Virtual Routers).  The



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   total number of certificates, and corresponding trust anchors, is
   very high, say hundreds.  Each of these policies is configured with
   one or more acceptable trust anchors, so that in total, the gateway
   has one hundred (100) trust anchors that could possibly used to
   authenticate an incoming connection.  Assume that many of those
   connections originate from hosts/gateways with dynamically assigned
   IP addresses, so that the source IP of the IKE initiator is not known
   to the gateway, nor is the identity of the initiator (until it is
   revealed in Main Mode message 5).  In IKE main mode message 4, the
   responder gateway will need to send a CERTREQ to the initiator.
   Given this example, the gateway will have no idea which of the
   hundred possible Certification Authorities to send in the CERTREQ.
   Sending all possible Certification Authorities will cause significant
   processing delays, bandwidth consumption, and UDP fragmentation, so
   this tactic is ruled out.

   In such a deployment, the responder gateway implementation should be
   able to do all it can to indicate a Certification Authority in the
   CERTREQ.  This means the responder SHOULD first check SPD to see if
   it can match the source IP, and find some indication of which CA is
   associated with that IP.  If this fails (because the source IP is not
   familiar, as in the case above), then the responder SHOULD have a
   configuration option specifying which CAs are the default CAs to
   indicate in CERTREQ during such ambiguous connections (e.g. send
   CERTREQ with these N CAs if there is an unknown source IP).  If such
   a fall-back is not configured or impractical in a certain deployment
   scenario, then the responder implementation SHOULD have both of the
   following configuration options:

   o  send a CERTREQ payload with an empty Certification Authority
      field, or
   o  terminate the negotiation with an appropriate error message and
      audit log entry.

   Receiving a CERTREQ payload with an empty Certification Authority
   field indicates that the recipient should send all/any end-entity
   certificates it has, regardless of the trust anchor.  The initiator
   should be aware of what policy and which identity it will use, as it
   initiated the connection on a matched policy to begin with, and can
   thus respond with the appropriate certificate.

   If, after sending an empty CERTREQ in Main Mode message 4, a
   responder receives a certificate in message 5 that chains to a trust
   anchor that the responder either (a) does NOT support, or (b) was not
   configured for the policy (that policy was now able to be matched due
   to having the initiator's certificate present), this MUST be treated
   as an error and security association setup MUST be aborted.  This
   event SHOULD be auditable.



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   Instead of sending a empty CERTREQ, the responder implementation MAY
   be configured to terminate the negotiation on the grounds of a
   conflict with locally configured security policy.

   The decision of which to configure is a matter of local security
   policy, this document RECOMMENDS that both options be presented to
   administrators.

   More examples, and explanation on this issue are included in "More on
   Empty CERTREQs" (Appendix B).

3.2.9.  Robustness

3.2.9.1.  Unrecognized or Unsupported Certificate Types

   Implementations MUST be able to deal with receiving CERTREQs with
   unsupported Certificate Types.  Absent any recognized and supported
   CERTREQ types, implementations MAY treat them as if they are of a
   supported type with the Certification Authority field left empty,
   depending on local policy.  ISAKMP [2] Section 5.10 "Certificate
   Request Payload Processing" specifies additional processing.

3.2.9.2.  Undecodable Certification Authority Fields

   Implementations MUST be able to deal with receiving CERTREQs with
   undecodable Certification Authority fields.  Implementations MAY
   ignore such payloads, depending on local policy.  ISAKMP specifies
   other actions which may be taken.

3.2.9.3.  Ordering of Certificate Request Payloads

   Implementations MUST NOT assume that CERTREQs are ordered in any way.

3.2.10.  Optimizations

3.2.10.1.  Duplicate Certificate Request Payloads

   Implementations SHOULD NOT send duplicate CERTREQs during an
   exchange.

3.2.10.2.  Name Lowest 'Common' Certification Authorities

   When a peer's certificate keying material has been cached, an
   implementation can send a hint to the peer to elide some of the
   certificates the peer would normally include in the response.  In
   addition to the normal set of CERTREQs that are sent specifying the
   trust anchors, an implementation MAY send CERTREQs specifying the
   relevant cached end-entity certificates.  When sending these hints,



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   it is still necessary to send the normal set of trust anchor CERTREQs
   because the hints do not sufficiently convey all of the information
   required by the peer.  Specifically, either the peer may not support
   this optimization or there may be additional chains that could be
   used in this context but will not be if only the end-entity
   certificate is specified.

   No special processing is required on the part of the recipient of
   such a CERTREQ, and the end-entity certificates will still be sent.
   On the other hand, the recipient MAY elect to elide certificates
   based on receipt of such hints.

   CERTREQs must contain information that identifies a Certification
   Authority certificate, which results in the peer always sending at
   least the end-entity certificate.  Always sending the end-entity
   certificate allows implementations to determine unambiguously when a
   new certificate is being used by a peer (perhaps because the previous
   certificate has just expired), which may result in a failure because
   a new intermediate CA certificate might not be available to validate
   the new end-entity certificate).  Implementations which implement
   this optimization MUST recognize when the end-entity certificate has
   changed and respond to it by not performing this optimization if the
   exchange must be retried so that any missing keying materials will be
   sent during retry.

3.2.10.3.  Example

   Imagine that an IKEv1 implementation has previously received and
   cached the peer certificate chain TA->CA1->CA2->EE.  If during a
   subsequent exchange this implementation sends a CERTREQ containing
   the Subject field in certificate TA, this implementation is
   requesting that the peer send at least 3 certificates: CA1, CA2, and
   EE.  On the other hand, if this implementation also sends a CERTREQ
   containing the Subject field of CA2, the implementation is providing
   a hint that only 1 certificate needs to be sent: EE.  Note that in
   this example, the fact that TA is a trust anchor should not be
   construed to imply that TA is a self-signed certificate.

3.3.  Certificate Payload

   The Certificate (CERT) Payload allows the peer to transmit a single
   certificate or CRL.  Multiple certificates should be transmitted in
   multiple payloads.  For backwards compatibility reasons,
   implementations MAY send intermediate CA certificates in addition to
   the appropriate end-entity certificate(s), but SHOULD NOT send any
   CRLs, ARLs, or trust anchors.  Exchanging trust anchors and
   especially CRLs and ARLs in IKE would increase the liklihood of UDP
   fragmentation, make the IKE exchange more complex, and consume



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   additional network bandwidth.

   Note, however, that while the sender of the CERT payloads SHOULD NOT
   send any trust anchors, it's possible that the recipient may consider
   any given intermediate CA certificate to be a trust anchor.  For
   instance, imagine the sender has the certificate chain TA1->CA1->EE1
   while the recipient has the certificate chain TA2->EE2 where TA2=CA1.
   The sender is merely including an intermediate CA certificate, while
   the recipient receives a trust anchor.

   However, not all certificate forms that are legal in the PKIX
   certificate profile make sense in the context of IPsec.  The issue of
   how to represent IKE-meaningful name-forms in a certificate is
   especially problematic.  This document provides a profile for a
   subset of the PKIX certificate profile that makes sense for IKEv1/
   ISAKMP and IKEv2.

3.3.1.  Certificate Type

   The Certificate Type field identifies to the peer the type of
   certificate keying materials that are included.  ISAKMP defines 10
   types of Certificate Data that can be sent and specifies the syntax
   for these types, and IKEv2 specifies 3 additional types.  For the
   purposes of this document, only the following types are relevant:

   o  X.509 Certificate - Signature
   o  Revocation Lists (CRL and ARL)
   o  PKCS #7 wrapped X.509 certificate
   o  IKEv2's Hash and URL of X.509 certificate

   The use of the other types are out of the scope of this document:

   o  X.509 Certificate - Key Exchange
   o  PGP Certificate
   o  DNS Signed Key
   o  Kerberos Tokens
   o  SPKI Certificate
   o  X.509 Certificate Attribute
   o  IKEv2's Raw RSA Key
   o  IKEv2's Hash and URL of X.509 bundle

3.3.2.  X.509 Certificate - Signature

   This type specifies that Certificate Data contains a certificate used
   for signing.






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3.3.3.  Revocation Lists (CRL and ARL)

   These types specify that Certificate Data contains an X.509 CRL or
   ARL.  These types SHOULD NOT be sent in IKE.  See Section 3.2.3 for
   discussion.

3.3.4.  IKEv2's Hash and URL of X.509 Certificate

   This type specifies that Certificate Data contains a hash and the URL
   to a repository where an X.509 certificate can be retrieved.

   An implementation that sends a HTTP_CERT_LOOKUP_SUPPORTED
   notification MUST support the http scheme and MAY support the ftp
   scheme, and MUST NOT require any specific form of the url-path and it
   SHOULD support having user-name, password and port parts in the URL.
   The following are examples of mandatory forms:

   o  http://certs.example.com/certificate.cer
   o  http://certs.example.com/certs/cert.pl?u=foo;a=pw;valid-to=+86400
   o  http://certs.example.com/%0a/../foo/bar/zappa

   while the following is an example of a form that SHOULD be supported:

   o  http://user:password@certs.example.com:8888/certificate.cer

   The following is an example of the ftp scheme that MAY be supported:

   o  ftp://ftp.example.com/pub/certificate.cer

3.3.5.  PKCS #7 wrapped X.509 certificate

   This type defines a particular encoding, not a particular certificate
   type.  Implementations SHOULD NOT generate CERTs that contain this
   Certificate Type.  Implementations SHOULD accept CERTs that contain
   this Certificate Type because several implementations are known to
   generate them.  Note that those implementations sometimes include
   entire certificate hierarchies inside a single CERT PKCS #7 payload,
   which violates the requirement specified in ISAKMP that this payload
   contain a single certificate.

3.3.6.  Location of Certificate Payloads

   In IKEv1 Main Mode, the CERT payload MUST be in messages 5 and 6.  In
   IKEv2, the CERT payload MUST be in messages 3 and 4.  Note that in
   IKEv2, it is possible to have one side authenticating with
   certificates while the other side authenticates with preshared keys.





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3.3.7.  Certificate Payloads Not Mandatory

   An implementation which does not receive any CERTREQs during an
   exchange SHOULD NOT send any CERT payloads, except when explicitly
   configured to proactively send CERT payloads in order to interoperate
   with non-compliant implementations which fail to send CERTREQs even
   when certificates are desired.  In this case, an implementation MAY
   send the certificate chain (not including the trust anchor)
   associated with the end-entity certificate.  This MUST NOT be the
   default behavior of implementations.

   Implementations whose local security policy configuration expects
   that a peer must receive certificates through out-of-band means
   SHOULD ignore any CERTREQ messages that are received.  Such a
   condition has been known to occur due to non-compliant or buggy
   implementations.

   Implementations that receive CERTREQs from a peer which contain only
   unrecognized Certification Authorities SHOULD NOT continue the
   exchange, in order to avoid unnecessary and potentially expensive
   cryptographic processing, denial-of-service (resource starvation)
   attacks.

3.3.8.  Response to Multiple Certification Authority Proposals

   In response to multiple CERTREQs which contain different
   Certification Authority identities, implementations MAY respond using
   an end-entity certificate which chains to a CA that matches any of
   the identities provided by the peer.

3.3.9.  Using Local Keying Materials

   Implementations MAY elect to skip parsing or otherwise decoding a
   given set of CERTs if equivalent keying materials are available via
   some preferable means, such as the case where certificates from a
   previous exchange have been cached.

3.3.10.  Multiple End-Entity Certificates

   Implementations SHOULD NOT send multiple end-entity certificates and
   recipients SHOULD NOT be expected to iterate over multiple end-entity
   certificates.

   If multiple end-entity certificates are sent, they MUST have the same
   public key, otherwise the responder does not know which key was used
   in the Main Mode message 5.





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3.3.11.  Robustness

3.3.11.1.  Unrecognized or Unsupported Certificate Types

   Implementations MUST be able to deal with receiving CERTs with
   unrecognized or unsupported Certificate Types.  Implementations MAY
   discard such payloads, depending on local policy.  ISAKMP [2] Section
   5.10 "Certificate Request Payload Processing" specifies additional
   processing.

3.3.11.2.  Undecodable Certificate Data Fields

   Implementations MUST be able to deal with receiving CERTs with
   undecodable Certificate Data fields.  Implementations MAY discard
   such payloads, depending on local policy.  ISAKMP specifies other
   actions which may be taken.

3.3.11.3.  Ordering of Certificate Payloads

   For IKEv1, implementations MUST NOT assume that CERTs are ordered in
   any way.  For IKEv2, implementations MUST NOT assume that any except
   the first CERT is ordered in any way.  IKEv2 specifies that the first
   CERT contain an end-entity certificate which can be used to
   authenticate the peer.

3.3.11.4.  Duplicate Certificate Payloads

   Implementations MUST support receiving multiple identical CERTs
   during an exchange.

3.3.11.5.  Irrelevant Certificates

   Implementations MUST be prepared to receive certificates and CRLs
   which are not relevant to the current exchange.  Implementations MAY
   discard such extraneous certificates and CRLs.

   Implementations MAY send certificates which are irrelevant to an
   exchange.  One reason for including certificates which are irrelevant
   to an exchange is to minimize the threat of leaking identifying
   information in exchanges where CERT is not encrypted.  It should be
   noted, however, that this probably provides rather poor protection
   against leaking the identity.

   Another reason for including certificates that seem irrelevant to an
   exchange is that there may be two chains from the Certification
   Authority to the end entity, each of which is only valid with certain
   validation parameters (such as acceptable policies).  Since the end-
   entity doesn't know which parameters the relying party is using, it



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   should send the certificates needed for both chains (even if there's
   only one CERTREQ).

   Implementations SHOULD NOT send multiple end-entity certificates and
   recipients SHOULD NOT be expected to iterate over multiple end-entity
   certificates.

3.3.12.  Optimizations

3.3.12.1.  Duplicate Certificate Payloads

   Implementations SHOULD NOT send duplicate CERTs during an exchange.
   Such payloads should be suppressed.

3.3.12.2.  Send Lowest 'Common' Certificates

   When multiple CERTREQs are received which specify certificate
   authorities within the end-entity certificate chain, implementations
   MAY send the shortest chain possible.  However, implementations
   SHOULD always send the end-entity certificate.  See Section 3.2.10.2
   for more discussion of this optimization.

3.3.12.3.  Ignore Duplicate Certificate Payloads

   Implementations MAY employ local means to recognize CERTs that have
   already been received and SHOULD discard these duplicate CERTs.

3.3.12.4.  Hash Payload

   IKEv1 specifies the optional use of the Hash Payload to carry a
   pointer to a certificate in either of the Phase 1 public key
   encryption modes.  This pointer is used by an implementation to
   locate the end-entity certificate that contains the public key that a
   peer should use for encrypting payloads during the exchange.

   Implementations SHOULD include this payload whenever the public
   portion of the keypair has been placed in a certificate.


4.  Certificate Profile

   Except where specifically stated in this document, implementations
   MUST conform to the requirements of the PKIX [5] certificate profile.

4.1.  X.509 Certificates

   Users deploying IKE and IPsec with certificates have often had little
   control over the capabilities of CAs available to them.



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   Implementations of this specification may include configuration knobs
   to disable checks required by this specification in order to permit
   use with inflexible and/or noncompliant CAs.  However, all checks on
   certificates exist for a specific reason involving the security of
   the entire system.  Therefore, all checks MUST be enabled by default.
   Administrators and users ought to understand the security purpose for
   the various checks, and be clear on what security will be lost by
   disabling the check.

4.1.1.  Versions

   Although PKIX states that "implementations SHOULD be prepared to
   accept any version certificate", in practice this profile requires
   certain extensions that necessitate the use of Version 3 certificates
   for all but self-signed certificates used as trust anchors.
   Implementations that conform to this document MAY therefore reject
   Version 1 and Version 2 certificates in all other cases.

4.1.2.  Subject

   Certification Authority implementations MUST be able to create
   certificates with Subject fields with at least the following four
   attributes: CN, C, O, OU.  Implementations MAY support other Subject
   attributes as well.  The contents of these attributes SHOULD be
   configurable on a certificate by certificate basis, as these fields
   will likely be used by IKE implementations to match SPD policy.

   See Section 3.1.5 for details on how IKE implementations need to be
   able to process Subject field attributes for SPD policy lookup.

4.1.2.1.  Empty Subject Name

   IKE Implementations MUST accept certificates which contain an empty
   Subject field, as specified in the PKIX certificate profile.
   Identity information in such certificates will be contained entirely
   in the SubjectAltName extension.

4.1.2.2.  Specifying Hosts and not FQDN in the Subject Name

   Implementations which desire to place host names that are not
   intended to be processed by recipients as FQDNs (for instance
   "Gateway Router") in the Subject MUST use the commonName attribute.

4.1.2.3.  EmailAddress

   As specified in the PKIX certificate profile, implementations MUST
   NOT populate X.500 distinguished names with the emailAddress
   attribute.



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4.1.3.  X.509 Certificate Extensions

   Conforming IKE implementations MUST recognize extensions which must
   or may be marked critical according to this specification.  These
   extensions are: KeyUsage, SubjectAltName, and BasicConstraints.

   Certification Authority implementations SHOULD generate certificates
   such that the extension criticality bits are set in accordance with
   the PKIX certifiate profile and this document.  With respect to
   compliance with the PKIX certificate profile, IKE implementations
   processing certificates MAY ignore the value of the criticality bit
   for extensions that are supported by that implementation, but MUST
   support the criticality bit for extensions that are not supported by
   that implementation.  That is, a peer processes all the extensions it
   is aware of whether the bit is true or false -- the bit says what
   happens when a peer cannot process an extension.


          implements    bit in cert     PKIX mandate    behavior
          ------------------------------------------------------
          yes           true            true            ok
          yes           true            false           ok or reject
          yes           false           true            ok or reject
          yes           false           false           ok
          no            true            true            reject
          no            true            false           reject
          no            false           true            reject
          no            false           false           ok


4.1.3.1.  AuthorityKeyIdentifier and SubjectKeyIdentifier

   Implementations SHOULD NOT assume support for the
   AuthorityKeyIdentifier or SubjectKeyIdentifier extensions, and thus
   Certification Authority implementations SHOULD NOT generate
   certificate hierarchies which are overly complex to process in the
   absence of these extensions, such as those that require possibly
   verifying a signature against a large number of similarly named CA
   certificates in order to find the CA certificate which contains the
   key that was used to generate the signature.

4.1.3.2.  KeyUsage

   IKE uses an end-entity certificate in the authentication process.
   The end-entity certificate may be used for multiple applications.  As
   such, the CA can impose some constraints on the manner that a public
   key ought to be used.  The KeyUsage (KU) and ExtendedKeyUsage (EKU)
   extensions apply in this situation.



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   Since we are talking about using the public key to validate a
   signature, if the KeyUsage extension is present, then at least one of
   the digitalSignature or the nonRepudiation bits in the KeyUsage
   extension MUST be set (both can be set as well).  It is also fine if
   other KeyUsage bits are set.

   A summary of the logic flow for peer cert validation follows:

   o  If no KU extension, continue.
   o  If KU present and doesn't mention digitalSignature or
      nonRepudiation (both, in addition to other KUs, is also fine),
      reject cert.
   o  If none of the above, continue.

4.1.3.3.  PrivateKeyUsagePeriod

   The PKIX certificate profile recommends against the use of this
   extension.  The PrivateKeyUsageExtension is intended to be used when
   signatures will need to be verified long past the time when
   signatures using the private keypair may be generated.  Since IKE SAs
   are short-lived relative to the intended use of this extension in
   addition to the fact that each signature is validated only a single
   time, the usefulness of this extension in the context of IKE is
   unclear.  Therefore, Certification Authority implementations MUST NOT
   generate certificates that contain the PrivateKeyUsagePeriod
   extension.  If an IKE implementation receives a certificate with this
   set, it SHOULD ignore it.

4.1.3.4.  CertificatePolicies

   Many IKE implementations do not currently provide support for the
   CertificatePolicies extension.  Therefore, Certification Authority
   implementations that generate certificates which contain this
   extension SHOULD NOT mark the extension as critical.

4.1.3.5.  PolicyMappings

   Many IKE implementations do not support the PolicyMappings extension.
   Therefore, implementations that generate certificates which contain
   this extension SHOULD NOT mark the extension as critical.

4.1.3.6.  SubjectAltName

   Deployments that intend to use an ID of FQDN, USER_FQDN, IPV4_ADDR,
   or IPV6_ADDR MUST issue certificates with the corresponding
   SubjectAltName fields populated with the same data.  Implementations
   SHOULD generate only the following GeneralName choices in the
   SubjectAltName extension, as these choices map to legal IKEv1/ISAKMP/



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   IKEv2 Identification Payload types: rfc822Name, dNSName, or
   iPAddress.  Although it is possible to specify any GeneralName choice
   in the Identification Payload by using the ID_DER_ASN1_GN ID type,
   implementations SHOULD NOT assume support for such functionality, and
   SHOULD NOT generate certificates that do so.

4.1.3.6.1.  dNSName

   This field MUST contain a fully qualified domain name.  If the IKE ID
   type is FQDN then the dNSName field MUST match its contents.
   Implementations MUST NOT generate names that contain wildcards.
   Implementations MAY treat certificates that contain wildcards in this
   field as syntactically invalid.

   Although this field is in the form of an FQDN, IKE implementations
   SHOULD NOT assume that this field contains an FQDN that will resolve
   via the DNS, unless this is known by way of some out-of-band
   mechanism.  Such a mechanism is out of the scope of this document.
   Implementations SHOULD NOT treat the failure to resolve as an error.

4.1.3.6.2.  iPAddress

   If the IKE ID type is IPV4_ADDR or IPV6_ADDR then the iPAddress field
   MUST match its contents.  Note that although PKIX permits CIDR [15]
   notation in the "Name Constraints" extension, the PKIX certificate
   profile explicitly prohibits using CIDR notation for conveying
   identity information.  In other words, the CIDR notation MUST NOT be
   used in the SubjectAltName extension.

4.1.3.6.3.  rfc822Name

   If the IKE ID type is USER_FQDN then the rfc822Name field MUST match
   its contents.  Although this field is in the form of an Internet mail
   address, IKE implementations SHOULD NOT assume that this field
   contains a valid email address, unless this is known by way of some
   out-of-band mechanism.  Such a mechanism is out of the scope of this
   document.

4.1.3.7.  IssuerAltName

   Certification Authority implementations SHOULD NOT assume that other
   implementations support the IssuerAltName extension, and especially
   should not assume that information contained in this extension will
   be displayed to end users.

4.1.3.8.  SubjectDirectoryAttributes

   The SubjectDirectoryAttributes extension is intended to convey



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   identification attributes of the subject.  IKE implementations MAY
   ignore this extension when it is marked non-critical, as the PKIX
   certificate profile mandates.

4.1.3.9.  BasicConstraints

   The PKIX certificate profile mandates that CA certificates contain
   this extension and that it be marked critical.  IKE implementations
   SHOULD reject CA certificates that do not contain this extension.
   For backwards compatibility, implementations may accept such
   certificates if explicitly configured to do so, but the default for
   this setting MUST be to reject such certificates.

4.1.3.10.  NameConstraints

   Many IKE implementations do not support the NameConstraints
   extension.  Since the PKIX certificate profile mandates that this
   extension be marked critical when present, Certification Authority
   implementations which are interested in maximal interoperability for
   IKE SHOULD NOT generate certificates which contain this extension.

4.1.3.11.  PolicyConstraints

   Many IKE implementations do not support the PolicyConstraints
   extension.  Since the PKIX certificate profile mandates that this
   extension be marked critical when present, Certification Authority
   implementations which are interested in maximal interoperability for
   IKE SHOULD NOT generate certificates which contain this extension.

4.1.3.12.  ExtendedKeyUsage

   The CA SHOULD NOT include the ExtendedKeyUsage (EKU) extension in
   certificates for use with IKE.  Note that there were three IPsec
   related object identifiers in EKU that were assigned in 1999.  The
   semantics of these values were never clearly defined.  The use of
   these three EKU values in IKE/IPsec is obsolete and explicitly
   deprecated by this specification.  CAs SHOULD NOT issue certificates
   for use in IKE with them.  (For historical reference only, those
   values were id-kp-ipsecEndSystem, id-kp-ipsecTunnel, and id-kp-
   ipsecUser.)

   The CA SHOULD NOT mark the EKU extension in certificates for use with
   IKE and one or more other applications.  Nevertheless, this document
   defines an ExtendedKeyUsage keyPurposeID that MAY be used to limit a
   certificate's use:






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      id-kp-ipsecIKE OBJECT IDENTIFIER ::= { id-kp 17 }

   where id-kp is defined in RFC-3280 [5].  If a certificate is intended
   to be used with both IKE and other applications, and one of the other
   applications requires use of an EKU value, then such certificates
   MUST contain either the keyPurposeID id-kp-ipsecIKE or
   anyExtendedKeyUsage [5] as well as the keyPurposeID values associated
   with the other applications.  Similarly, if a CA issues multiple
   otherwise-similar certificates for multiple applications including
   IKE, and it is intended that the IKE certificate NOT be used with
   another application, the IKE certificate MAY contain an EKU extension
   listing a keyPurposeID of id-kp-ipsecIKE to discourage its use with
   the other application.  Recall however, EKU extensions in
   certificates meant for use in IKE are NOT RECOMMENDED.

   A summary of the logic flow for peer certificate validation regarding
   the EKU extension follows:

   o  If no EKU extension, continue.
   o  If EKU present AND contains either id-kp-ipsecIKE or
      anyExtendedKeyUsage, continue.
   o  Otherwise, reject cert.

4.1.3.13.  CRLDistributionPoints

   Because this document deprecates the sending of CRLs in-band, the use
   of CRLDistributionPoints (CDP) becomes very important if CRLs are
   used for revocation checking (as opposed to say Online Certificate
   Status Protocol - OCSP [16]).  The IPsec peer either needs to have a
   URL for a CRL written into its local configuration, or it needs to
   learn it from CDP.  Therefore, Certification Authority
   implementations SHOULD issue certificates with a populated CDP.

   Failure to validate the CRLDistributionPoints/
   IssuingDistributionPoint pair can result in CRL substitution where an
   entity knowingly substitutes a known good CRL from a different
   distribution point for the CRL which is supposed to be used which
   would show the entity as revoked.  IKE implementations MUST support
   validating that the contents of CRLDistributionPoints match those of
   the IssuingDistributionPoint to prevent CRL substitution when the
   issuing CA is using them.  At least one CA is known to default to
   this type of CRL use.  See Section 4.2.2.5 for more information.

   CDPs SHOULD be "resolvable".  Several non-compliant Certification
   Authority implementations are well known for including unresolvable
   CDPs like http://localhost/path_to_CRL and http:///path_to_CRL which
   are equivalent to failing to include the CDP extension in the
   certificate.



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   See the IETF IPR web page for CRLDistributionPoints intellectual
   property rights (IPR) information.  Note that both the
   CRLDistributionPoints and IssuingDistributionPoint extensions are
   RECOMMENDED but not REQUIRED by the PKIX certificate profile, so
   there is no requirement to license any IPR.

4.1.3.14.  InhibitAnyPolicy

   Many IKE implementations do not support the InhibitAnyPolicy
   extension.  Since the PKIX certificate profile mandates that this
   extension be marked critical when present, Certification Authority
   implementations which are interested in maximal interoperability for
   IKE SHOULD NOT generate certificates which contain this extension.

4.1.3.15.  FreshestCRL

   IKE implementations MUST NOT assume that the FreshestCRL extension
   will exist in peer certificates.  Note that most IKE implementations
   do not support delta CRLs.

4.1.3.16.  AuthorityInfoAccess

   The PKIX certificate profile defines the AuthorityInfoAccess
   extension, which is used to indicate "how to access CA information
   and services for the issuer of the certificate in which the extension
   appears."  Because this document deprecates the sending of CRLs in-
   band, the use of AuthorityInfoAccess (AIA) becomes very important if
   OCSP [16] is to be used for revocation checking (as opposed to CRLs).
   The IPsec peer either needs to have a URI for the OCSP query written
   into its local configuration, or it needs to learn it from AIA.
   Therefore, implementations SHOULD support this extension, especially
   if OCSP will be used.

4.1.3.17.  SubjectInfoAccess

   The PKIX certificate profile defines the SubjectInfoAccess
   certificate extension, which is used to indicate "how to access
   information and services for the subject of the certificate in which
   the extension appears."  This extension has no known use in the
   context of IPsec.  Conformant IKE implementations SHOULD ignore this
   extension when present.

4.2.  X.509 Certificate Revocation Lists

   When validating certificates, IKE implementations MUST make use of
   certificate revocation information, and SHOULD support such
   revocation information in the form of CRLs, unless non-CRL revocation
   information is known to be the only method for transmitting this



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   information.  Deployments that intend to use CRLs for revocation
   SHOULD populate the CRLDistributionPoints extension.  Therefore
   Certification Authority implementations MUST support issuing
   certificates with this field populated.  IKE implementations MAY
   provide a configuration option to disable use of certain types of
   revocation information, but that option MUST be off by default.  Such
   an option is often valuable in lab testing environments.

4.2.1.  Multiple Sources of Certificate Revocation Information

   IKE implementations which support multiple sources of obtaining
   certificate revocation information MUST act conservatively when the
   information provided by these sources is inconsistent: when a
   certificate is reported as revoked by one trusted source, the
   certificate MUST be considered revoked.

4.2.2.  X.509 Certificate Revocation List Extensions

4.2.2.1.  AuthorityKeyIdentifier

   Certification Authority implementations SHOULD NOT assume that IKE
   implementations support the AuthorityKeyIdentifier extension, and
   thus SHOULD NOT generate certificate hierarchies which are overly
   complex to process in the absence of this extension, such as those
   that require possibly verifying a signature against a large number of
   similarly named CA certificates in order to find the CA certificate
   which contains the key that was used to generate the signature.

4.2.2.2.  IssuerAltName

   Certification Authority implementations SHOULD NOT assume that IKE
   implementations support the IssuerAltName extension, and especially
   should not assume that information contained in this extension will
   be displayed to end users.

4.2.2.3.  CRLNumber

   As stated in the PKIX certificate profile, all issuers MUST include
   this extension in all CRLs.

4.2.2.4.  DeltaCRLIndicator

4.2.2.4.1.  If Delta CRLs Are Unsupported

   IKE implementations that do not support delta CRLs MUST reject CRLs
   which contain the DeltaCRLIndicator (which MUST be marked critical
   according to the PKIX certficate profile) and MUST make use of a base
   CRL if it is available.  Such implementations MUST ensure that a



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   delta CRL does not "overwrite" a base CRL, for instance in the keying
   material database.

4.2.2.4.2.  Delta CRL Recommendations

   Since some IKE implementations that do not support delta CRLs may
   behave incorrectly or insecurely when presented with delta CRLs,
   administrators and deployers should consider whether issuing delta
   CRLs increases security before issuing such CRLs.  And, if all the
   elements in the VPN and PKI systems do not adequately support Delta
   CRLs, then their use should be questioned.

   The editors are aware of several implementations which behave in an
   incorrect or insecure manner when presented with delta CRLs.  See
   Appendix A for a description of the issue.  Therefore, this
   specification RECOMMENDS NOT issuing delta CRLs at this time.  On the
   other hand, failure to issue delta CRLs may expose a larger window of
   vulnerability if a full CRL is not issued as often as delta CRLs
   would be.  See the Security Considerations section of the PKIX [5]
   certificate profile for additional discussion.  Implementors as well
   as administrators are encouraged to consider these issues.

4.2.2.5.  IssuingDistributionPoint

   A CA that is using CRLDistributionPoints may do so to provide many
   "small" CRLs, each only valid for a particular set of certificates
   issued by that CA.  To associate a CRL with a certificate, the CA
   places the CRLDistributionPoints extension in the certificate, and
   places the IssuingDistributionPoint in the CRL.  The
   distributionPointName field in the CRLDistributionPoints extension
   MUST be identical to the distributionPoint field in the
   IssuingDistributionPoint extension.  At least one CA is known to
   default to this type of CRL use.  See Section 4.1.3.13 for more
   information.

4.2.2.6.  FreshestCRL

   Given the recommendations against Certification Authority
   implementations generating delta CRLs, this specification RECOMMENDS
   that implementations do not populate CRLs with the FreshestCRL
   extension, which is used to obtain delta CRLs.

4.3.  Strength of Signature Hashing Algorithms

   At the time that this document is being written, popular
   certification authorities and CA software issue certificates using
   the RSA-with-SHA1 and RSA-with-MD5 signature algorithms.
   Implementations MUST be able to validate certificates with either of



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   those algorithms.

   As described in [17], both the MD5 and SHA-1 hash algorithms are
   weaker than originally expected with respect to hash collisions.
   Certificates that use these hash algorithms as part of their
   signature algorithms could conceivably be subject to an attack where
   a CA issues a certificate with a particular identity, and the
   recipient of that certificate can create a different valid
   certificate with a different identity.  So far, such an attack is
   only theoretical, even with the weaknesses found in the hash
   algorithms.

   Because of the recent attacks, there has been a heightened interest
   in having widespread deployment of additional signature algorithms.
   The algorithm that has been mentioned most often is RSA-with-SHA256,
   two types of which are described in detail in [18].  It is widely
   expected that this signature algorithm will be much more resilient to
   collision-based attacks than the current RSA-with-SHA1 and RSA-with-
   MD5, although no proof of that has been shown.  There is active
   discussion in the cryptographic community of better hash functions
   that could be used in signature algorithms.

   In order to interoperate, all implementations need to be able to
   validate signatures for all algorithms that the implementations will
   encounter.  Therefore, implementations SHOULD be able to use
   signatures that use the sha256WithRSAEncryption signature algorithm
   (PKCS#1 version 1.5) as soon as possible.  At the time that this
   document is being written, there is at least one CA that supports
   generating certificates with sha256WithRSAEncryption signature
   algorithm and it is expected that there will be significant
   deployment of this algorithm by the end of 2007.


5.  Configuration Data Exchange Conventions

   Below we present a common format for exchanging configuration data.
   Implementations MUST support these formats, MUST support receiving
   arbitrary whitespace at the beginning and end of any line, MUST
   support receiving arbitrary line lengths although they SHOULD
   generate lines less than 76 characters, and MUST support receiving
   the following three line-termination disciplines: LF (US-ASCII 10),
   CR (US-ASCII 13), and CRLF.

5.1.  Certificates

   Certificates MUST be Base64 [19] encoded and appear between the
   following delimiters:




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       -----BEGIN CERTIFICATE-----
       -----END CERTIFICATE-----

5.2.  CRLs and ARLs

   CRLs and ARLs MUST be Base64 encoded and appear between the following
   delimiters:

       -----BEGIN CRL-----
       -----END CRL-----

5.3.  Public Keys

   IKE implementations MUST support two forms of public keys:
   certificates and so-called "raw" keys.  Certificates should be
   transferred in the same form as Section 5.1.  A raw key is only the
   SubjectPublicKeyInfo portion of the certificate, and MUST be Base64
   encoded and appear between the following delimiters:

       -----BEGIN PUBLIC KEY-----
       -----END PUBLIC KEY-----

5.4.  PKCS#10 Certificate Signing Requests

   A PKCS#10 [9] Certificate Signing Request MUST be Base64 encoded and
   appear between the following delimiters:

       -----BEGIN CERTIFICATE REQUEST-----
       -----END CERTIFICATE REQUEST-----


6.  Acknowledgements

   The authors would like to acknowledge the expired draft-ietf-ipsec-
   pki-req-05.txt for providing valuable materials for this document.

   The authors would like to especially thank Eric Rescorla, one of its
   original authors, in addition to Greg Carter, Steve Hanna, Russ
   Housley, Charlie Kaufman, Tero Kivinen, Pekka Savola, Paul Hoffman,
   and Gregory Lebovitz for their valuable comments, some of which have
   been incorporated verbatim into this document.  Paul Knight performed
   the arduous tasks of coverting the text to XML format.


7.  Security Considerations






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7.1.  Certificate Request Payload

   The Contents of CERTREQ are not encrypted in IKE.  In some
   environments this may leak private information.  Administrators in
   some environments may wish to use the empty Certification Authority
   option to prevent such information from leaking, at the cost of
   performance.

7.2.  IKEv1 Main Mode

   Certificates may be included in any message, and therefore
   implementations may wish to respond with CERTs in a message that
   offers privacy protection, in Main Mode messages 5 and 6.
   Implementations may not wish to respond with CERTs in the second
   message, thereby violating the identity protection feature of Main
   Mode in IKEv1.

7.3.  Disabling Certificate Checks

   It is important to note that anywhere this document suggests
   implementors provide users with the configuration option to simplify,
   modify, or disable a feature or verification step, there may be
   security consequences for doing so.  Deployment experience has shown
   that such flexibility may be required in some environments, but
   making use of such flexibility can be inappropriate in others.  Such
   configuration options MUST default to "enabled" and it is appropriate
   to provide warnings to users when disabling such features.


8.  IANA Considerations

   There are no known numbers which IANA will need to manage.


9.  References

9.1.  Normative References

   [1]  Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
        RFC 2409, November 1998.

   [2]  Maughan, D., Schneider, M., and M. Schertler, "Internet Security
        Association and Key Management Protocol (ISAKMP)", RFC 2408,
        November 1998.

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




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   [4]  Kent, S. and R. Atkinson, "Security Architecture for the
        Internet Protocol", RFC 2401, November 1998.

   [5]  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.

   [6]  Piper, D., "The Internet IP Security Domain of Interpretation
        for ISAKMP", RFC 2407, November 1998.

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

   [8]  Postel, J., "Internet Protocol", STD 5, RFC 791, September 1981.

   [9]  Kaliski, B., "PKCS #10: Certification Request Syntax Version
        1.5", RFC 2314, March 1998.

9.2.  Informative References

   [10]  Kent, S. and K. Seo, "Security Architecture for the Internet
         Protocol", RFC 4301, December 2005.

   [11]  Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6)
         Specification", RFC 2460, December 1998.

   [12]  Eastlake, D., "Domain Name System Security Extensions",
         RFC 2535, March 1999.

   [13]  Faltstrom, P., Hoffman, P., and A. Costello,
         "Internationalizing Domain Names in Applications (IDNA)",
         RFC 3490, March 2003.

   [14]  Lynn, C., Kent, S., and K. Seo, "X.509 Extensions for IP
         Addresses and AS Identifiers", RFC 3779, June 2004.

   [15]  Fuller, V., Li, T., Yu, J., and K. Varadhan, "Classless Inter-
         Domain Routing (CIDR): an Address Assignment and Aggregation
         Strategy", RFC 1519, September 1993.

   [16]  Myers, M., Ankney, R., Malpani, A., Galperin, S., and C. Adams,
         "X.509 Internet Public Key Infrastructure Online Certificate
         Status Protocol - OCSP", RFC 2560, June 1999.

   [17]  Hoffman, P. and B. Schneier, "Attacks on Cryptographic Hashes
         in Internet Protocols", RFC 4270, November 2005.

   [18]  Schaad, J., Kaliski, B., and R. Housley, "Additional Algorithms



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         and Identifiers for RSA Cryptography for use in the Internet
         X.509 Public Key Infrastructure Certificate and Certificate
         Revocation List (CRL) Profile", RFC 4055, June 2005.

   [19]  Josefsson, S., "The Base16, Base32, and Base64 Data Encodings",
         RFC 3548, July 2003.

   [20]  Y Lim and D. Singer, "MIME Type Registration for MPEG-4",
         RFC 4337, March 2006.


Appendix A.  The Possible Dangers of Delta CRLs

   The problem is that the CRL processing algorithm is sometimes written
   incorrectly with the assumption that all CRLs are base CRLs and it is
   assumed that CRLs will pass content validity tests.  Specifically,
   such implementations fail to check the certificate against all
   possible CRLs: if the first CRL that is obtained from the keying
   material database fails to decode, no further revocation checks are
   performed for the relevant certificate.  This problem is compounded
   by the fact that implementations which do not understand delta CRLs
   may fail to decode such CRLs due to the critical DeltaCRLIndicator
   extension.  The algorithm that is implemented in this case is
   approximately:

   o  fetch newest CRL
   o  check validity of CRL signature
   o  if CRL signature is valid then
   o  if CRL does not contain unrecognized critical extensions and
      certificate is on CRL then set certificate status to revoked

   The authors note that a number of PKI toolkits do not even provide a
   method for obtaining anything but the newest CRL, which in the
   presence of delta CRLs may in fact be a delta CRL, not a base CRL.

   Note that the above algorithm is dangerous in many ways.  See the
   PKIX [5] certificate profile for the correct algorithm.


Appendix B.  More on Empty CERTREQs

   Sending empty certificate requests is commonly used in
   implementations, and in the IPsec interop meetings, vendors have
   generally agreed that it means that send all/any end-entity
   certificates you have (if multiple end-entity certificates are sent,
   they must have same public key, as otherwise the other end does not
   know which key was used).  For 99% of cases the client have exactly
   one certificate and public key, so it really doesn't matter, but the



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   server might have multiple, thus it simply needs to say to the
   client, use any certificate you have.  If we are talking about
   corporate vpns etc, even if the client have multiple certificates or
   keys, all of them would be usable when authenticating to the server,
   so client can simply pick one.

   If there is some real difference on which certificate to use (like
   ones giving different permissions), then the client must be
   configured anyways, or it might even ask the user which one to use
   (the user is the only one who knows whether he needs admin
   privileges, thus needs to use admin cert, or is the normal email
   privileges ok, thus using email only cert).

   99% of the cases the client have exactly one certificate, so it will
   send it.  In 90% of the rest of the cases, any of the certificates is
   ok, as they are simply different certificates from same CA, or
   different CAs for the same corporate VPN, thus any of them is ok.

   Sending empty certificate requests has been agreed there to mean
   "give me your cert; any cert".

   Justification:

   o  Responder first does all it can to send a CERTREQ with a CA, check
      for IP match in SPD, have a default set of CAs to use in ambiguous
      cases, etc.
   o  sending empty CERTREQs is fairly common in implementations today,
      and is generally accepted to mean "send me a certificate, any
      certificate that works for you"
   o  saves responder sending potentially 100's of certs, the
      fragmentation problems that follow, etc.
   o  in +90% of use cases, Initiators have exactly 1 certificate
   o  in +90% of the remaining use cases, the multiple certificates it
      has are issued by the same CA
   o  in the remaining use case(s) -- if not all the others above -- the
      Initiator will be configured explicitly with which certificate to
      send, so responding to an empty CERTREQ is easy.

   The following example shows why initiators need to have sufficient
   policy definition to know which certificate to use for a given
   connection it initiates.

   EXAMPLE: Your client (initiator) is configured with VPN policies for
   gateways A and B (representing perhaps corporate partners).







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   The policies for the two gateways look something like:


         Acme Company policy (gateway A)
            Engineering can access 10.1.1.0
                   Trusted CA: CA-A, Trusted Users: OU=Engineering
            Partners can access 20.1.1.0
                   Trusted CA: CA-B, Trusted Users: OU=AcmePartners

         Bizco Company policy (gateway B)
           Sales can access 30.1.1.0
                   Trusted CA: CA-C, Trusted Users: OU=Sales
           Partners can access 40.1.1.0
                   Trusted CA: CA-B, Trusted Users: OU=BizcoPartners


   You are an employee of Acme and you are issued the following
   certificates:

   o  From CA-A: CN=JoeUser,OU=Engineering
   o  From CA-B: CN=JoePartner,OU=BizcoPartners

   The client MUST be configured locally to know which CA to use when
   connecting to either gateway.  If your client is not configured to
   know the local credential to use for the remote gateway, this
   scenario will not work either.  If you attempt to connect to Bizco,
   everything will work... as you are presented with responding with a
   certificate signed by CA-B or CA-C... as you only have a certificate
   from CA-B you are OK.  If you attempt to connect to Acme, you have an
   issue because you are presented with an ambiguous policy selection.
   As the initiator, you will be presented with certificate requests
   from both CA A and CA B. You have certificates issued by both CAs,
   but only one of the certificates will be usable.  How does the client
   know which certificate it should present?  It must have sufficiently
   clear local policy specifying which one credential to present for the
   connection it initiates.


Appendix C.  Change History

   [RFC Editor, please remove Change History prior to publication as an
   RFC]


      April 2006 (-10)






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      *  Many places - s/PKIX/the PKIX certificate profile/ (Russ
         Housley, AD Review)
      *  1 - removed text describing discussion of the document on
         pki4ipsec@icsalabs.com mailing list (Russ Housley, AD Review)
      *  3.1 - Better wording: "The Identification (ID) Payload
         indicates the identity claimed by the sender."  (Russ Housley,
         AD Review)
      *  Many places - s/2401bis/RFC 4301/ (Russ Housley, AD Review)
      *  3.1 - s/attribute/extension/ when talking about SubjectAltName
         (Russ Housley, AD Review)
      *  3.1 - s/attribute/value/ when talking about strings in
         certificates (Russ Housley, AD Review)
      *  3.1.2/3.1.3 - IDN is ok caseless comparison (Russ Housley, AD
         Review)
      *  3.1.4 - Change ref from SBGP to RFC 3779 (Russ Housley, AD
         Review)
      *  Many places - s/SubjectName/Subject/ (Russ Housley, AD Review)
      *  3.2 - add "(CRLs)" (Russ Housley, AD Review)
      *  3.2.1 - improved wording (Russ Housley, AD Review)
      *  3.2.8.2 - s/empty IssuerName fields/an empty Issuer field/
         (Russ Housley, AD Review)
      *  3.2.10.2 - s/keying materials have been/keying material has
         been/ (Russ Housley, AD Review)
      *  3.2.10.2 - s/respond with/include in the response/ (Russ
         Housley, AD Review)
      *  3.2.10.3 - s/SubjectName of CA2/CA2's Subject name/ (Russ
         Housley, AD Review)
      *  3.3 - improved wording (Russ Housley, AD Review)
      *  3.3.4 - changed ".crt" extension to ".cer" (for alignment with
         RFC 2585) (Russ Housley, AD Review)
      *  3.3.6 - made inconsitent musts both MUST (Russ Housley, AD
         Review)
      *  3.3.7 - s/denial of service/denial-of-service/ (Russ Housley,
         AD Review)
      *  4.1.2.3 - s/DistinguishedNames/X.500 distinguished names/ (Russ
         Housley, AD Review)
      *  4.1.3 - s/PKIX compliance/the PKIX certificate profile
         compliance/ (Russ Housley, AD Review)
      *  4.1.3 - s/PKIX and/the PKIX certificate profile and/ (Russ
         Housley, AD Review)
      *  4.1.3 - "Perhaps "peer" instead of "relyong party" should be
         used to match the rest of the document."  (Russ Housley, AD
         Review)
      *  4.1.3.13 - s/PKIX docs/the IETF IPR web page/ (Russ Housley, AD
         Review)
      *  4.2 - removed ambiguous "according to administrator's needs"
         (Russ Housley, AD Review)




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      *  4.2.2.3 - s/conforming to PKIX// (Russ Housley, AD Review)
      *  4.3 - at least 1 CA issues sha256WithRSAEncryption (Russ
         Housley, AD Review)
      *  5.1 - added reference for base64 (RFC3548) (Russ Housley, AD
         Review)
      *  s/[3]/[RFC 4306]/ (Russ Housley, AD Review)
      *  s/[10]/[RFC 4301]/ (Russ Housley, AD Review)
      *  s/[13]/[RFC 3779]/ (Russ Housley, AD Review)
      *  Moved CHANGE HISTORY to the end of the document (Russ Housley,
         AD Review)
      *  3.3.7 - point out strange case has been known to occur due to
         bugs (March 26, 2006 pki4ipsec from Pekka Savola)
      *  3.1.2/3.1.3 - make the example clearer that DNSSEC must be used
         for the dereference (March 26, 2006 pki4ipsec from Pekka
         Savola)
      *  3.2.5 - point out that going to IKE doc is for discussion of
         HTTP_CERT_LOOKUP_SUPPORTED (March 26, 2006 pki4ipsec from Pekka
         Savola)
      *  3.1 - added GN type to table (MUST NOT) (March 26, 2006
         pki4ipsec from Pekka Savola)
      *  3.1 - reordered table to match section order (March 26, 2006
         pki4ipsec from Pekka Savola)
      *  Fixed HTTP_LOOKUP_SUPPORTED to be HTTP_CERT_LOOKUP_SUPPORTED
         (March 26, 2006 pki4ipsec from Pekka Savola)


      February 2006 (-09)

      *  3.2.6/3.3.6 - clarified text, that it applies to Main Mode only
         (text was updated in -08 3.3.6, not 3.2.6, but needed to be
         fixed in both places) but not here)
      *  Moved text from security considerations regarding SHA-256


      February 2006 (-08)

      *  3.2.6 - clarified text, that it applies to Main Mode only
      *  Added text to security considerations regarding SHA-256 (30 Jan
         2005 pki4ipsec email from Paul Hoffman)


      November 2005 (-07)

      *  3.1 - renumbered table notes to avoid confusion with references
         (9 Nov 2005 pki4ipsec email from Jim Schaad)
      *  3.2.2 - changed "signing certificate" to "a certificate used
         for signing" (9 Nov 2005 pki4ipsec email from Jim Schaad)




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      *  4.1 - added text re: implications of disabling checks ("escape
         clause") (8 Nov 2005 pki4ipsec email from Bill Sommerfeld, 10
         Nov 2005 pki4ipsec email from Gregory M Lebovitz)
      *  4.1.3.2 - removed text from pseudocode: "If told (by
         configuration) to ignore KeyUsage (KU), accept certificate
         regardless of its markings."
      *  4.1.3.12 - replaced text with clearer text (8 Nov 2005
         pki4ipsec email from Bill Sommerfeld)
      *  4.1.3.12 - removed text from pseudocode: "If told (by
         configuration) to ignore ExtendedKeyUsage (EKU), accept cert
         regardless of the presence or absence of the extension."
      *  4.1.3.17 - removed gratuitous "private" modifier from
         SubjectInfoAccess section (9 Nov 2005 pki4ipsec email from Jim
         Schaad)
      *  4.2.2.4.2 - clarified delta CRL text so that it no longer could
         be read as implying that full CRLs can't be issued at the time
         a certificate is revoked. (9 Nov 2005 pki4ipsec email from Jim
         Schaad)
      *  Security Considerations - added "Disabling Certificate Checks"
         section


      October 2005 (-06)

      *  4.1.3.12 - added text re: id-kp-ipsecIKE


      July 2005 (-05)

      *  3.1 - added "See 2401bis, section 4.4.3.2 for more details." to
         resolve issue #561.
      *  3.1.10 - added text pointing to PAD in 2401bis to discussion of
         binding identity to policy.


      December 2004 (-04)

      *  Added Paul Hoffman's text from issue #708
      *  Added text explaining that it's possible for a recipient to
         receive CERT payloads containing certs that the recipient
         considers a trust anchor (15 Nov 2004 pki4ipsec email from
         Peter Williams)
      *  Replaced text in 4.1.3 with Kent's text (issue #655) (22 Nov
         2004 pki4ipsec email from Stephen Kent, Paul Hoffman)







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      September 2004 (-03)

      *  Minor editorial changes in abstract and introduction clarifing
         when something is from IPsec, IKE, etc
      *  Minor editorial changes throughout
      *  Fixed "Certification Authority" instead of "Certificate
         Authority"
      *  Cleaned up initiator/responder when really referred to sender/
         recipient
      *  Fixed inconsistancy in text by making sure that all text on the
         topic of sending CERTREQs follow Gregory Lebovitz's proposal
         for CERT payloads: "should deal with all the CRL, Intermediat
         Certs, Trust Anchors, etc OOB of IKE; MUST be able to send and
         receive EE cert payload; only real exception is Intermediate
         Cets which MAY be sent and SHOULD be able to be receivable (but
         in reality there are very few hierarchies in operation, so
         really it's a corner case); SHOULD NOT send the other stuff
         (CRL, Trust Anchors, etc) in cert payloads in IKE; SHOULD be
         able to accept the other stuff if by chance it gets sent,
         though we hope they don't get sent"
      *  3.1 - removed text suggesting that it would be reasonable to
         terminate IKEv2 processing if the initiator were to receive a
         responder-generated IDr
      *  3.1.1 - noted that certificates may contain multiple IP
         addresses
      *  3.1.9 - removed (temporarily?) confusing text stating that
         overlapping policies was prohibited, text which was
         inconsistent with text right above it
      *  3.2.7.2 - SHOULD changed to MUST terminate if peer's
         certificate chain violates local policy
      *  3.3 - removed text implying that pausing in the middle of an
         IKE exchange in order to obtain revocation status information
         via http or OCSP would reduce latency in IKE
      *  4.2 - allow deployments that don't wish to populate CDP (for
         instance if a source of revocation information is configured
         via some other means) to skip populating CDP, making consistent
         with 4.1.3.13 and the issues IPR spelled out in PKIX
      *  Somehow a CRL out-of-band configuration format had been
         omitted.
      *  #555: Kent-1.0 Introduction - document now references IKEv2
      *  #559: Kent-Profile Document 3.1.0 - use sender/recipient
         instead of agent
      *  #564: Kent-Profile Document 3.1.1 - specified that support for
         ID_IPV4_ADDR and/or ID_IPV6_ADDR are contingent on device
         support for IPv4 and/or IPv6
      *  #568: Kent-Profile document 3.1.4 - specified that there wasn't
         a standard and besides no one has implemented it




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      *  #571: Kent-Profile document 3.1.8 - tried to be even more
         clearer than was asked for by spelling things out in detail
      *  #572: Kent-Profile document 3.1.8 Formerly issue #18 - now
         specifies that it's only a local matter if that information is
         not coordinated with other administrators
      *  #573: Kent-Profile document 3.2.3/Myers - revocation
         information no longer exchanged in-band, plus Mike Myers has
         submitted an OCSP w/IKE draft, which is references by this
         document.
      *  #578 Kent-Profile document 4.0.0 - went through entire PKIX
         profile section and prefaced "implementation" with "IKE" or
         "Certification Authority" wherever it was sure to be one or the
         other
      *  #581: Kent-Profile document 4.1.3.9 - replaced description with
         text from RFC 2459
      *  #584: Maillist-Lebovitz PKI Life Cycle-Revocation - fixed
      *  #586: Maillist-Allison Empty CertReq - there is now lots of
         text dealing with when empty certreqs are permitted
      *  3.2.7.1 - CERTREQ only mandatory if in-band exchange of keymat
         is desired (28 Jul 2004 pki4ipsec email from jknowles@
         SonicWALL.com)
      *  3.3.6 - clarified that "non-compliant" means not sending a
         CERTREQ (28 Jul 2004 pki4ipsec email from jknowles@
         SonicWALL.com)
      *  3.2.7.1 - fixed contradition: mandatory to respond to CERTREQ
         UNLESS configured not to (28 Jul 2004 pki4ipsec email from
         jknowles@SonicWALL.com)
      *  3.2.9.2 and 3.2.9.3 - CERTREQ contains an issuer name only for
         IKEv2 (19 Sep 2004 email from Charlie Kaufman)
      *  Answered 'Section 3.1.9 para 2: "The initiator MUST know by
         policy..." is a difficult to interpret requirement.  It could
         mean that it must be possible to configure in policy which ID
         is to be sent.  Did you mean "the initiator must decide...",
         where the decision might be wired into a particular
         implementation?' by changing it to be merely descriptive, and
         to refer to policy configuration (19 Sep 2004 email from
         Charlie Kaufman)
      *  IPSEC -> IPsec (19 Sep 2004 email from Charlie Kaufman)
      *  3.1.1 para 1: "MUST be stored" changed to "MUST be encoded" (19
         Sep 2004 email from Charlie Kaufman)
      *  3.1.5 para 2 - made it clear that empty SubjectNames are
         permitted by PKIX in certificates, but this document doesn't
         permit them in ID (19 Sep 2004 email from Charlie Kaufman)
      *  3.2.7.1 - clarified by specifying that it's a trust anchor
         that's being chosen, not end-entity certificate (19 Sep 2004
         email from Charlie Kaufman)





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      *  3.3.9.5 - fixed confusing last paragraph (19 Sep 2004 email
         from Charlie Kaufman)
      *  3.3.10.3 - made it more clear that this section is really
         talking about duplicate certificate payloads (19 Sep 2004 email
         from Charlie Kaufman)
      *  4.1.2.2 para 2 and 3 - moved to 3.1.x section where is belongs
         (19 Sep 2004 email from Charlie Kaufman)
      *  4.1.3.5 - the last sentence of 4.1.3.4 copied here (19 Sep 2004
         email from Charlie Kaufman)
      *  4.2.2.4.2 - SHOULD -> should (19 Sep 2004 email from Charlie
         Kaufman)
      *  3.2.5 and 3.3.4 - added description of URL scheme support (16
         Aug 2004 pki4ipsec email from Tero Kivinen)
      *  Removed 6.1 and 6.3 because they were either incorrect or
         didn't add any new security considerations above and beyond the
         IKE documents.
      August 2004 (-02) (Edited by Gregory Lebovitz, with XML formatting
      and cross-referencing by Paul Knight)

      *  3.1.1 the text between the **s was added to paragraph, per the
         question that arose in IETF60 WG session: Implementations MUST
         be capable of verifying that the address contained in the ID is
         the same as the peer source address **contained in the outer
         most IP header**.
      *  3.2.7 - added HTTP_CERT_LOOKUP_SUPPORTED to this section and
         described its use - #38
      *  3.3 - changed back sending of intermediate CA certificates from
         SHOULD NOT to MAY (for backward compatibility).  Added text to
         explain further why we want to stay away from actually doing it
         though.
      *  3.3.8 - changed text per Knowles/Korver 2004.07.28.
      *  3.3.9.5 - Change discard of Irrelevant Certificates from may to
         SHOULD - #23(Kent 2004.04.26)
      *  4.1.3.2 KU - re-worked to reflect discussion on list and in
         IETF60 - #36
      *  4.1.3.12 EKU - re-worked to reflect discussion on list and in
         IETF60 - #36
      *  [IKEv2] update the reference to the -14 draft of May 29, 2004


      July 2004 (-01) (Edited by Gregory Lebovitz)

      *  Changed ISAKMP references in Abstract and Intro to IKE.
      *  Editorial changes to make the text conform with the summary
         table in 3.1, especially in the text following the table in
         3.1.  Particular note should be paid to changes in section
         3.5.1.




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      *  Sect 3.1.1 - editorial changes to aid in clarification.  Added
         text on when deployers might consider using IP addr, but
         strongly encouraged not to.
      *  Sect 3.1.8 removed IP address from list of practically used ID
         types.
      *  3.1.9 overhauled (per Kivinen, July 18)
      *  3.2 - added IKEv2's Hash and URL of x.509 to list of those
         profiled and gave it its own section, now 3.2.5
      *  added note in CRL/ARL section about revocation occurring OOB of
         IKE
      *  deleted ARL as its own section and collapsed it into Revocation
         Lists (CRL and ARL) for consciseness.  Renumbered accordingly.
      *  Sect 3.2.7.2 - Changed from MUST not send empty certreqs to
         SHOULD send CERTREQs which contain CA fields with direction on
         how, but MAY send empty CERTREQs in certain case.  Use case
         added, and specifics of both initiator and responder behavior
         listed.
      *  APPENDIX C added to fill out the explanation (mostly discussion
         from list).
      *  3.3 - clarified that sending CRLs and chaining certs is
         deprecated.
      *  added IKEv2's Hash and URL of x.509 to list of those profiled
         and gave it its own section.  Condensed ARL into CRL and
         renumbered accordingly.
      *  duplicate section was removed, renumbered accordingly
      *  3.3.10.2 - title changed. sending chaining becomes SHOULD NOT.
      *  4.1.2 added text to explicity call out support for CN, C, O, OU
      *  collapsed 4.1.2.3 into 4.1.2.2 and renumbered accordingly.
      *  Collapsed 4.1.3.2 into 4.1.3.1 and renumbered accordingly
      *  Edited 4.1.3.2 Key Usage and 4.1.3.12 ExtKey Usage according to
         Hoffman, July18
      *  4.1.3.3 if receive cert w/ PKUP, ignore it.
      *  4.1.3.13 - CDP changed text to represent SHOULD issue, and how
         important CDP becomes when we do not send CRLs in-band.  Added
         SHOULD for CDPs actually being resolvable (reilly email).
      *  Reordered 6.4 for better clarity.
      *  Added Rescorla to Acknowledgements section, as he is no longer
         listed as an editor, since -00.


      May 2004 (renamed draft-ietf-pki4ipsec-ikecert-profile-00.txt)
      (edited by Brian Korver)

      *  Made it clearer that the format of the ID_IPV4_ADDR payload
         comes from RFC791 and is nothing new.  (Tero Kivinen Feb 29)
      *  Permit implementations to skip verifying that the peer source
         address matches the contents of ID_IPV{4,6}_ADDR.  (Tero
         Kivinen Feb 29, Gregory Lebovitz Feb 29)



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      *  Removed paragraph suggesting that implementations favor
         unauthenticated peer source addresses over an unauthenticated
         ID for initial policy lookup.  (Tero Kivinen Feb 29, Gregory
         Lebovitz Feb 29)
      *  Removed some text implying RSA encryption mode was in scope.
         (Tero Kivinen Feb 29)
      *  Relaxed deprecation of PKCS#7 CERT payloads.  (Tero Kivinen Feb
         29)
      *  Made it clearer that out-of-scope local heuristics should be
         used for picking an EE cert to use when generating CERTREQ, not
         when receiving CERTREQ.  (Tero Kivinen Feb 29)
      *  Made it clearer that CERT processing can be skipped when the
         contents of a CERT are already known.  (Tero Kivinen Feb 29)
      *  Implementations SHOULD generate BASE64 lines less than 76
         characters.  (Tero Kivinen Feb 29)
      *  Added "Except where specifically stated in this document,
         implementations MUST conform to the requirements of PKIX"
         (Steve Hanna Oct 7, 2003)
      *  RECOMMENDS against populating the ID payload with IP addresses
         due to interoperability issues such as problem with NAT
         traversal.  (Gregory Lebovitz May 14)
      *  Changed "as revoked by one source" to "as revoked by one
         trusted source".  (Michael Myers, May 15)
      *  Specifying Certificate Authorities section needed to be
         regularized with Gregory Lebovitz's CERT proposal from -04.
         (Tylor Allison, May 15)
      *  Added text specifying how recipients SHOULD NOT be expected to
         iterate over multiple end-entity certs.  (Tylor Allison, May
         15)
      *  Modified text to refer to IKEv2 as well as IKEv1/ISAKMP where
         relevant.
      *  IKEv2: Explained that IDr sent by responder doesn't have to
         match the [IDr] sent initiator in second exchange.
      *  IKEv2: Noted that "The identity ... does not necessarily have
         to match anything in the CERT payload" (S3.5) is not
         contradicted by SHOULD in this document.
      *  IKEv2: Noted that ID_USER_FQDN renamed to ID_RFC822_ADDR, and
         ID_USER_FQDN would be used exclusively in this document.
      *  IKEv2: Declared that 3 new CERTREQ and CERT types are not
         profiled in this document (well, at least not yet, pending WG
         discussion of what to do -- note that they are only SHOULDs in
         IKEv2).
      *  IKEv2: Noted that CERTREQ payload changed from DN to SHA-1 of
         SubjectPublicKeyInfo.
      *  IKEv2: Noted new requirement that specifies that the first
         certificate sent MUST be the EE cert (section 3.6).





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      February 2004 (-04)

      *  Minor editorial changes to clean up language
      *  Deprecate in-band exchange of CRLs
      *  Incorporated Gregory Lebovitz's proposal for CERT payloads:
         "should deal with all the CRL, Intermediat Certs, Trust
         Anchors, etc OOB of IKE; MUST be able to send and receive EE
         cert payload; only real exception is Intermediate Cets which
         MAY be sent and SHOULD be able to be receivable (but in reality
         there are very few hierarchies in operation, so really it's a
         corner case); SHOULD NOT send the other stuff (CRL, Trust
         Anchors, etc) in cert payloads in IKE; SHOULD be able to accept
         the other stuff if by chance it gets sent, though we hope they
         don't get sent"
      *  Incorporated comments contained in Oct 7, 2003 email from
         steve.hanna@sun.com to ipsec@lists.tislabs.com
      *  Moved text from "Profile of ISAKMP" Background section to each
         payload section (removing duplication of these sections)
      *  Removed "Certificate-Related Playloads in ISAKMP" section since
         it was not specific to IKE.
      *  Incorporated Gregory Lebovitz's table in the "Identification
         Payload" section
      *  Moved text from "binding identity to policy" sections to each
         payload section
      *  Moved text from "IKE" section into now-combined "IKE/ISAKMP"
         section
      *  ID_USER_FQDN and ID_FQDN promoted to MUST from MAY
      *  Promoted sending ID_DER_ASN1_DN to MAY from SHOULD NOT, and
         receiving from MUST from MAY
      *  Demoted ID_DER_ASN1_GN to MUST NOT
      *  Demoted populating SubjectName in place of populating the
         dNSName from SHOULD NOT to MUST NOT and removed the text
         regarding domainComponent
      *  Revocation information checking MAY now be disabled, although
         not by default
      *  Aggressive Mode removed from this profile


      June 2003 (-03)

      *  Minor editorial changes to clean up language
      *  Minor additional clarifying text
      *  Removed hyphenation
      *  Added requirement that implementations support configuration
         data exchange having arbitrary line lengths






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      February 2003 (-02)

      *  Word choice: move from use of "root" to "trust anchor", in
         accordance with PKIX
      *  SBGP note and reference for placing address subnet and range
         information into certificates
      *  Clarification of text regarding placing names of hosts into the
         Name commonName attribute of SubjectName
      *  Added table to clarify text regarding processing of the
         certificate extension criticality bit
      *  Added text underscoring processing requirements for
         CRLDistributionPoints and IssuingDistributionPoint


      October 2002, Reorganization (-01)


      June 2002, Initial Draft (-00)

































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Author's Address

   Brian Korver
   Network Resonance, Inc.
   2483 E. Bayshore Rd.
   Palo Alto, CA  94303
   US

   Phone: +1 650 812 7705
   Email: briank@networkresonance.com









































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