draft-ietf-pkix-pi-06.txt

PKIX的RFC英文文档

PKIX Working Group                                      D. Pinkas (Bull)
INTERNET-DRAFT                                           T. Gindin (IBM)
Expires: June 2003                                         December 2002
Target category: Standard Track



                 Internet X.509 Public Key Infrastructure

                          Permanent Identifier

                       <draft-ietf-pkix-pi-06.txt>


Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of [RFC 2026].

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that other
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   Copyright (C) The Internet Society (2002). All Rights Reserved.

   Please send comments on this document to the [e-mail]
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Abstract

   This document define a new form of name, called permanent 
   identifier, that may be included in the subjectAltName extension 
   of a public key certificate issued to an entity.

   The permanent identifier is an optional feature that may be used 
   by a CA to indicate that the certificate relates to the same 
   entity even if the name or the affiliation of that entity stored 
   in the subject or another name form in the subjectAltName extension 
   has changed.

   The subject name, carried in the subject field, is only unique 
   for each subject entity certified by the one CA as defined by the 
   issuer name field. Also, the new name form can carry a 
   name that is unique for each subject entity certified by a CA.

Pinkas, Gindin                                                 [ Page 1]


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1  Introduction

   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.

   This specification is based on RFC 3280, which defines underlying 
   certificate formats and semantics needed for a full implementation 
   of this standard.

   The subject field of a public key certificate identifies the entity 
   associated with the public key stored in the subject public key 
   field. Names and identities of a subject may be carried in the 
   subject field and/or the subjectAltName extension. Where subject 
   field is non-empty, it MUST contain an X.500 distinguished 
   name (DN). The DN MUST be unique for each subject entity certified 
   by a single CA as defined by the issuer name field.

   The subject name changes whenever any of the components of that 
   name gets changed. There are several reasons for such a change to 
   happen.

         For employees of a company or organization, the person may get 
         a different position within the same company and thus will 
         move from one organization unit to another one. Including the 
         organization unit in the name may however be very useful to 
         allow the relying parties (RP's) using that certificate to 
         identify the right individual.

         For citizens, an individual may change their name by legal 
         processes, especially women as a result of marriage.

         Any certificate subject identified by geographical location may
         relocate and change at least some of the location attributes 
         (e.g. country name, state or province, locality, or street).

   A permanent identifier consists of an identifier value assigned
   within a given naming space by the organization which is 
   authoritative for that naming space.  Such an organization is known 
   as an Assigner Authority.

   An Assigner Authority may be a government, a government agency, a
   corporation, or any other sort of organization.  It MUST have a 
   unique identifier to distinguish it from any other such authority.
   In this standard, that identifier MUST be an object identifier or 
   be representable as a URI.

   A permanent identifier may be useful in three contexts: access 
   control, non-repudiation and audit records.

         For access control, the permanent identifier may be used in 
         an ACL (Access Control List) instead of the DN or any other 
         form of name and would not need to be changed, even if the 
         subject name of the entity changes.

Pinkas, Gindin                                                 [ Page 2]


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         For non-repudiation, the permanent identifier may be used to 
         link different transactions to the same entity, even when 
         the subject name of the entity changes.

         For audit records, the permanent identifier may be used to 
         link different audit records to the same entity, even when 
         the subject name of the entity changes.

   When two certificates from different CA's contain both the same 
   permanent identifier value and the same type of permanent 
   identifier from a given Assigner Authority, then these 
   certificates relate to the same entity, whatever the content of 
   the DN or other subjectAltName components may be.

2. Definition of a Permanent Identifier

   A CA which includes a permanent identifier in a certificate is 
   certifying that any public key certificate containing that 
   identifier refers to the same entity, whatever the content of 
   the DN or other subjectAltName components may be.

   The use of a permanent identifier is OPTIONAL. This name is 
   defined as a form of otherName from the GeneralName structure in 
   SubjectAltName. The permanent identifier is defined as follows:

   id-on-permanentIdentifier   OBJECT IDENTIFIER ::= { id-on 3 }

     PermanentIdentifier ::=     SEQUENCE {
        identifierValue              IdentifierValue,
        identifierType               IdentifierType OPTIONAL,
        matchingRule        [0]      IMPLICIT OBJECT IDENTIFIER OPTIONAL
     }

     IdentifierValue ::= CHOICE {
            iA5String            IA5String,
            uTF8String           UTF8String
     }

     IdentifierType ::= CHOICE {
            registeredOID                   OBJECT IDENTIFIER,
            uri                             IA5String
     }

   The IdentifierValue supports two syntaxes: IA5String or UTF8String.
   IA5String is variable length data of ASCII octets. UTF8String is 
   variable length data of octets. UTF-8 is an ASCII-preserving 
   encoding method for Unicode (ISO 10646), the Universal Character Set 
   (UCS). The UCS allows to support most of the world's writing systems 
   using a single character set.

   The IdentifierType field, when present, identifies both the 
   Assigner Authority and the type of that field.



Pinkas, Gindin                                                 [ Page 3]


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   When the IdentifierType field is missing, then it is assumed that 
   the Assigner Authority is the CA itself and that there is only one 
   type of such identifier for the CA.

   The IdentifierType field may contain either:

           a) an Object Identifier (i.e. an OID), or
           b) a permanent URI using IA5String.

   Characteristically, when an OID is used, the prefix of the OID 
   identifies the Assigner Authority, and a suffix is used to identify 
   the type of permanent identifier being identified. Essentially the 
   same thing is true of URI's.

   Note: the full arc of the object identifier used to identify the 
   permanent identifier name form is derived using:

     id-pkix OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) 
        dod(6) internet(1) security(5) mechanisms(5) pkix(7) }

     id-on OBJECT IDENTIFIER ::= { id-pkix 8 }   -- other name forms

   If identifierType is missing, then the permanent identifier is 
   locally unique to the CA.

   If identifierType is present, then the permanent identifier is 
   globally unique among all CAs.

   The matchingRule is an OID. When the OID is missing the 
   following matching rule SHALL be used:

      The Alphanumeric Identifier Match rule compares for equality a
      presented value with an attribute value of type UTF8String 
      or IA5String, which is interpreted as a series of alphanumeric 
      characters.  The rules for matching are that a working comparison 
      value is constructed from each of the two values by including 
      only the digits and alphabetic characters appearing in the value; 
      and then the two comparison values are compared using 
      CaseIgnoreMatch.  This rule is intended for use only with 
      identifiers in variants of the Latin, Greek, and Cyrillic scripts.

   Note: other matching rules can be used (see in chapter 6 of X.520). 
   Two such examples are:

     caseIgnoreMatch {2 5 13 2} defined in section 6.1.1 of X.520, and 
     caseExactMatch  {2 5 13 5} defined in section 6.1.4 of X.520.

3. Security considerations

   A given entity may have at an instant of time or at different 
   instants of time multiple forms of identities. 




Pinkas, Gindin                                                 [ Page 4]


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   If the permanent identifier is locally unique to the CA (i.e. 
   identifierType is not present), then two certificates from the 
   same CA can be compared. When they contain two identical permanent 
   identifiers, then a relying party may determine that they refer to 
   the same entity.

   If the permanent identifier is globally unique among all CAs (i.e. 
   identifierType is present), then two certificates from different 
   CAs can be compared. When they contain two identical permanent 
   identifiers, then a relying party may determine that they refer to 
   the same entity. It is the responsibility of the CA to verify that 
   the permanent identifier being included in the certificate refers 
   to the subject being certified.

   The permanent identifier identifies the entity, irrespective of any 
   attribute extension. When a public key certificate contains 
   attribute extensions, the permanent identifier, if present, should 
   not be used for access control purposes but only for audit purposes. 
   The reason is that since these attributes may change, access could 
   be granted on attributes that were originally present in a 
   certificate issued to that entity but are no more present in the 
   current certificate.

   The content and the format of the IdentifierValue are defined by 
   the Assigner Authority. An Assigner Authority who wishes to permit 
   IdentifierValues to be matched using a matching rule different from 
   the one specified in this document would be required to specify a 
   matching rule. Many such matching rules are specified in ITU-T X.520.

   Subject names in certificates are chosen by the issuing CA and are 
   mandated to be unique for each CA; so there can be no name collision 
   between subject names from the same CA. These names may be an 
   end-entity name, when the certificate is a leaf certificate or a 
   CA name, when it is a CA certificate.

   Since a name is only unique towards its superior CA, unless some 
   naming constraints are being used, a name would only be guaranteed 
   to be globally unique when considered to include a sequence of all 
   the names of the superior CAs.  Thus, two certificates which contain 
   a permanent identifier extension without a identifierType may have 
   their permanent identifier extensions compared for equality either 
   by comparing the public key values of the two CAs which have issued 
   these two certificates or by comparing the sequence of CA names in 
   the certification path from the trust anchor to the CA, inclusive.

   The certification of different CAs with the same DN by different 
   CAs has other negative consequences in various parts of the PKI, 
   notably rendering the IssuerAndSerialNumber structure in RFC 2630 
   section 5.3 ambiguous.






Pinkas, Gindin                                                 [ Page 5]


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4. References

4.1. Normative

   [RFC 2026] S. Bradner, "The Internet Standards Process - Revision 3"
   November 1996.

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

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

4.2. Informative

   [X.501]  ITU-T Recommendation X.501 (1997 E): Information Technology
   - Open Systems Interconnection - The Directory: Models, June 1997.