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Network Working Group
Request for Comments: 2986
Obsoletes: 2314
Category: Informational
M. Nystrom
B. Kaliski
RSA Security
November 2000

PKCS #10: Certification Request Syntax Specification

Version 1.7

Status of this Memo

This memo provides information for the Internet community. It does not specify an Internet standard of any kind. Distribution of this memo is unlimited.

Copyright Notice

Copyright © The Internet Society (2000). All Rights Reserved.

Abstract

This memo represents a republication of PKCS #10 v1.7 from RSA Laboratories' Public-Key Cryptography Standards (PKCS) series, and change control is retained within the PKCS process. The body of this document, except for the security considerations section, is taken directly from the PKCS #9 v2.0 or the PKCS #10 v1.7 document.

This memo describes a syntax for certification requests.

Table of Contents

   1.  Introduction ................................................. 2
   2.  Definitions and notation ..................................... 2
   2.1  Definitions ................................................. 2
   2.2  Notation .................................................... 4
   3.  Overview ..................................................... 4
   4.  Certification request syntax ................................. 5
   4.1  CertificationRequestInfo .................................... 5
   4.2  CertificationRequest ........................................ 7
   5.  Security Considerations ...................................... 8
   6.  Authors' Addresses ........................................... 8
   A.  ASN.1 module ................................................. 9
   B.  Intellectual property considerations ........................ 10
   C.  Revision history ............................................ 10
   D.  References .................................................. 11
   E.  Contact information & About PKCS ............................ 12
   Full Copyright Statement ........................................ 14

1. Introduction

This document describes syntax for certification requests. A certification request consists of a distinguished name, a public key, and optionally a set of attributes, collectively signed by the entity requesting certification. Certification requests are sent to a certification authority, which transforms the request into an X.509 [9] public-key certificate. (In what form the certification authority returns the newly signed certificate is outside the scope of this document. A PKCS #7 [2] message is one possibility.)

The intention of including a set of attributes is twofold: to provide other information about a given entity , or a "challenge password" by which the entity may later request certificate revocation; and to provide attributes for inclusion in X.509 certificates. A non- exhaustive list of attributes is given in PKCS #9 [3].

Certification authorities may also require non-electronic forms of request and may return non-electronic replies. It is expected that descriptions of such forms, which are outside the scope of this document, will be available from certification authorities.

The preliminary intended application of this document is to support PKCS #7 cryptographic messages, but it is expected that other applications will be developed (see e.g. [4]).

2. Definitions and notation

 2.1 Definitions

For the purposes of this document, the following definitions apply. 

   ALGORITHM       An information object class defined in X.509 to
                   describe objects composed of an algorithm (a unique
                   object identifier) and its parameters (any ASN.1
                   type).  The values of objects in this class can be
                   represented by the ASN.1 type AlgorithmIdentifier{}.
                   ALGORITHM is defined as the "useful" information
                   object class TYPE-IDENTIFIER, specified in [11],
                   Annex A.

AlgorithmIdentifier{}

A useful parameterized version of X.509 type AlgorithmIdentifier is defined in this document. This type tightly binds pairs of algorithm object identifiers to their associated parameter types. When referenced, the single parameter of AlgorithmIdentifier{} specifies a constraint on the pairs of values that may appear in that instance of the type. The encoded values of AlgorithmIdentifier{} are equivalent to those of type AlgorithmIdentifier. 

   ASN.1           Abstract Syntax Notation One, as defined in the ASN.1
                   standards ([10], [11], [12], and [13]).
   
   ATTRIBUTE       This class describes objects composed of an attribute
                   (a unique object identifier) and an associated set of
                   attribute values (any ASN.1 type).  The values of
                   objects in this class can be represented by type
                   Attribute{}.
   
   Attribute{}     A useful parameterized version of X.501 [8] type
                   Attribute is defined in this document.  This type
                   tightly binds pairs of attribute type object
                   identifiers to one or more attribute values types.
                   In the ASN.1 open type notation, an attribute type is
                   defined as ATTRIBUTE.&id and an attribute value as
                   ATTRIBUTE.&Type.  When referenced, the single
                   parameter of Attribute{} specifies a constraint on
                   the pairs of values that may appear in an instance of
                   the type.  The encoded values of Attribute{} are
                   equivalent to those of type Attribute.
   
   BER             Basic Encoding Rules for ASN.1, as defined in X.690
                   ([14]).
   
   Certificate     A type that binds a subject entity's distinguished
                   name to a public key with a digital signature.  This
                   type is defined in X.509.  This type also contains
                   the distinguished name of the certificate issuer (the
                   signer), an issuer-specific serial number, the
                   issuer's signature algorithm identifier, a validity
                   period, and an optional set of certificate
                   extensions.
   
   DER             Distinguished Encoding Rules for ASN.1, as defined in
                   X.690.  DER is a subset of BER.
   
   Name            A type that uniquely identifies or "distinguishes"
                   objects in an X.500 [7] directory.  This type is
                   defined in X.501.  In an X.509 certificate, the type
                   identifies the certificate issuer and the certificate
                   subject, the entity whose public key is certified.
  
  2.2 Notation

No special notation is used in this document.

3. Overview

A certification request consists of three parts: "certification request information," a signature algorithm identifier, and a digital signature on the certification request information. The certification request information consists of the entity's distinguished name, the entity's public key, and a set of attributes providing other information about the entity.

The process by which a certification request is constructed involves the following steps:

  1. A CertificationRequestInfo value containing a subject distinguished name, a subject public key, and optionally a set of attributes is constructed by an entity requesting certification.
  1. The CertificationRequestInfo value is signed with the subject entity's private key. (See Section 4.2.)

3. The CertificationRequestInfo value, a signature algorithm

identifier, and the entity's signature are collected together

into a CertificationRequest value, defined below.

A certification authority fulfills the request by authenticating the requesting entity and verifying the entity's signature, and, if the request is valid, constructing an X.509 certificate from the distinguished name and public key, the issuer name, and the certification authority's choice of serial number, validity period, and signature algorithm. If the certification request contains any PKCS #9 attributes, the certification authority may also use the values in these attributes as well as other information known to the certification authority to construct X.509 certificate extensions.

In what form the certification authority returns the new certificate is outside the scope of this document. One possibility is a PKCS #7 cryptographic message with content type signedData, following the degenerate case where there are no signers. The return message may include a certification path from the new certificate to the certification authority. It may also include other certificates such as cross-certificates that the certification authority considers helpful, and it may include certificate-revocation lists (CRLs). Another possibility is that the certification authority inserts the new certificate into a central database.

Note 1 - An entity would typically send a certification request after generating a public-key/private-key pair, but may also do so after a change in the entity's distinguished name.

Note 2 - The signature on the certification request prevents an entity from requesting a certificate with another party's public key. Such an attack would give the entity the minor ability to pretend to be the originator of any message signed by the other party. This attack is significant only if the entity does not know the message being signed and the signed part of the message does not identify the signer. The entity would still not be able to decrypt messages intended for the other party, of course.

Note 3 - How the entity sends the certification request to a certification authority is outside the scope of this document. Both paper and electronic forms are possible.

Note 4 - This document is not compatible with the certification request syntax for Privacy-Enhanced Mail, as described in RFC 1424 [5]. The syntax here differs in three respects: It allows a set of attributes; it does not include issuer name, serial number, or validity period; and it does not require an "innocuous" message to be signed. This document is designed to minimize request size, an important feature for certification authorities accepting requests on paper.

4. Certification request syntax

This section is divided into two parts. The first part describes the certification-request-information type CertificationRequestInfo, and the second part describes the top-level type CertificationRequest. 

 4.1 CertificationRequestInfo

Certification request information shall have ASN.1 type CertificationRequestInfo: 

   CertificationRequestInfo ::= SEQUENCE {
        version       INTEGER { v1(0) } (v1,...),
        subject       Name,
        subjectPKInfo SubjectPublicKeyInfo{{ PKInfoAlgorithms }},
        attributes    [0] Attributes{{ CRIAttributes }}
   }
   
   SubjectPublicKeyInfo { ALGORITHM : IOSet} ::= SEQUENCE {
        algorithm        AlgorithmIdentifier {{IOSet}},
        subjectPublicKey BIT STRING
   }

PKInfoAlgorithms ALGORITHM ::= {

... -- add any locally defined algorithms here -- }

   Attributes { ATTRIBUTE:IOSet } ::= SET OF Attribute{{ IOSet }}
   
   CRIAttributes  ATTRIBUTE  ::= {
        ... -- add any locally defined attributes here -- }
   
   Attribute { ATTRIBUTE:IOSet } ::= SEQUENCE {
        type   ATTRIBUTE.&id({IOSet}),
        values SET SIZE(1..MAX) OF ATTRIBUTE.&Type({IOSet}{@type})
   }

The components of type CertificationRequestInfo have the following meanings:

version is the version number, for compatibility with future

revisions of this document. It shall be 0 for this version of the standard.

subject is the distinguished name of the certificate subject

(the entity whose public key is to be certified).

subjectPublicKeyInfo contains information about the public key

being certified. The information identifies the entity's public-key algorithm (and any associated parameters); examples of public-key algorithms include the rsaEncryption object identifier from PKCS #1 [1]. The information also includes a bit-string representation of the entity's public key. For the public-key algorithm just mentioned, the bit string contains the DER encoding of a value of PKCS #1 type RSAPublicKey. The values of type SubjectPublicKeyInfo{} allowed for subjectPKInfo are constrained to the values specified by the information object set PKInfoAlgorithms, which includes the extension marker (...). Definitions of specific algorithm objects are left to specifications that reference this document. Such specifications will be interoperable with their future versions if any additional algorithm objects are added after the extension marker.

attributes is a collection of attributes providing additional

information about the subject of the certificate. Some attribute types that might be useful here are defined in PKCS #9. An example is the challenge-password attribute, which specifies a password by which the entity may request certificate revocation. Another example is information to appear in X.509 certificate extensions (e.g. the extensionRequest attribute from PKCS #9). The values of type

Attributes{} allowed for attributes are constrained to the values specified by the information object set CRIAttributes. Definitions of specific attribute objects are left to specifications that reference this document. Such specifications will be interoperable with their future versions if any additional attribute objects are added after the extension marker. 

 4.2 CertificationRequest

A certification request shall have ASN.1 type CertificationRequest: 

   CertificationRequest ::= SEQUENCE {
        certificationRequestInfo CertificationRequestInfo,
        signatureAlgorithm AlgorithmIdentifier{{ SignatureAlgorithms }},
        signature          BIT STRING
   }
   
   AlgorithmIdentifier {ALGORITHM:IOSet } ::= SEQUENCE {
        algorithm          ALGORITHM.&id({IOSet}),
        parameters         ALGORITHM.&Type({IOSet}{@algorithm}) OPTIONAL
   }

SignatureAlgorithms ALGORITHM ::= {

... -- add any locally defined algorithms here -- }

The components of type CertificationRequest have the following meanings:

certificateRequestInfo is the "certification request

information." It is the value being signed.

signatureAlgorithm identifies the signature algorithm (and any

associated parameters) under which the certification-request information is signed. For example, a specification might include an ALGORITHM object for PKCS #1's md5WithRSAEncryption in the information object set SignatureAlgorithms: 

          SignatureAlgorithms ALGORITHM ::= {
               ...,
               { NULL IDENTIFIED BY md5WithRSAEncryption }
          }

signature is the result of signing the certification request

information with the certification request subject's private key.

The signature process consists of two steps:

  1. The value of the certificationRequestInfo component is DER encoded, yielding an octet string.

2. The result of step 1 is signed with the certification request

subject's private key under the specified signature

algorithm, yielding a bit string, the signature.

Note - An equivalent syntax for CertificationRequest could be written: 

   CertificationRequest ::= SIGNED { EncodedCertificationRequestInfo }
        (CONSTRAINED BY { -- Verify or sign encoded
         -- CertificationRequestInfo -- })

EncodedCertificationRequestInfo ::= 

        TYPE-IDENTIFIER.&Type(CertificationRequestInfo)
   
   SIGNED { ToBeSigned } ::= SEQUENCE {
        toBeSigned ToBeSigned,
        algorithm  AlgorithmIdentifier { {SignatureAlgorithms} },
        signature  BIT STRING
   }

5. Security Considerations

Security issues are discussed throughout this memo.

6. Authors' Addresses

Magnus Nystrom
RSA Security
Box 10704
S-121 29 Stockholm
Sweden

EMail: 

          magnus@rsasecurity.com

Burt Kaliski
RSA Security
20 Crosby Drive
Bedford, MA 01730 USA

EMail: 

          bkaliski@rsasecurity.com

APPENDICES

A. ASN.1 Module

This appendix includes all of the ASN.1 type and value definitions contained in this document in the form of the ASN.1 module PKCS-10. 

   PKCS-10 {iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
   pkcs-10(10) modules(1) pkcs-10(1)}

DEFINITIONS IMPLICIT TAGS ::= 

   BEGIN
   
   -- EXPORTS All --

-- All types and values defined in this module are exported for use -- in other ASN.1 modules. 

   IMPORTS

informationFramework, authenticationFramework 

        FROM UsefulDefinitions {joint-iso-itu-t(2) ds(5) module(1)
        usefulDefinitions(0) 3}

ATTRIBUTE, Name 

        FROM InformationFramework informationFramework

ALGORITHM

FROM AuthenticationFramework authenticationFramework;

   -- Certificate requests
   CertificationRequestInfo ::= SEQUENCE {
        version       INTEGER { v1(0) } (v1,...),
        subject       Name,
        subjectPKInfo SubjectPublicKeyInfo{{ PKInfoAlgorithms }},
        attributes    [0] Attributes{{ CRIAttributes }}
   }
   
   SubjectPublicKeyInfo {ALGORITHM: IOSet} ::= SEQUENCE {
        algorithm        AlgorithmIdentifier {{IOSet}},
        subjectPublicKey BIT STRING
   }

PKInfoAlgorithms ALGORITHM ::= {

... -- add any locally defined algorithms here -- }

   Attributes { ATTRIBUTE:IOSet } ::= SET OF Attribute{{ IOSet }}
   CRIAttributes  ATTRIBUTE  ::= {
        ... -- add any locally defined attributes here -- }
   
   Attribute { ATTRIBUTE:IOSet } ::= SEQUENCE {
        type   ATTRIBUTE.&id({IOSet}),
        values SET SIZE(1..MAX) OF ATTRIBUTE.&Type({IOSet}{@type})
   }
   
   CertificationRequest ::= SEQUENCE {
        certificationRequestInfo CertificationRequestInfo,
        signatureAlgorithm AlgorithmIdentifier{{ SignatureAlgorithms }},
        signature          BIT STRING
   }
   
   AlgorithmIdentifier {ALGORITHM:IOSet } ::= SEQUENCE {
        algorithm  ALGORITHM.&id({IOSet}),
        parameters ALGORITHM.&Type({IOSet}{@algorithm}) OPTIONAL
   }

SignatureAlgorithms ALGORITHM ::= {

... -- add any locally defined algorithms here -- }

   END

B. Intellectual property considerations

RSA Security makes no patent claims on the general constructions described in this document, although specific underlying techniques may be covered.

License to copy this document is granted provided that it is identified as "RSA Security Inc. Public-Key Cryptography Standards (PKCS)" in all material mentioning or referencing this document.

RSA Security makes no representations regarding intellectual property claims by other parties. Such determination is the responsibility of the user.

C. Revision history

   Version 1.0

Version 1.0 was the previous version of this document (also published as "version 1.5" in [6]). 

   Version 1.7

This version incorporates several editorial changes, including updates to the references, and changes to ASN.1 type definitions. The following substantive changes have been made: 

         - This version refers to X.680-X.690, the current international
           standards for ASN.1 and its encoding rules.  All references
           to X.208 and X.209 have been eliminated.
  • The X.690 standard requires that the encoded values of SET OF components be sorted in ascending order under DER. Regardless of this, applications should not rely on the ordering of attribute components.
  • All references to PKCS #6 Extended-Certificate Syntax Standard have been removed. With the addition of extensions to X.509 version 3 certificates, RSA Laboratories is withdrawing support for PKCS #6.

Note - The reason for using version 1.7 for this document is to avoid confusion with [6], which is named version 1.5, and an unsupported PKCS #10 version named Version 1.6.

D. References

   [1]  RSA Laboratories. PKCS #1: RSA Encryption Standard. Version 2.0,
   
        October 1998.
   
   [2]  RSA Laboratories. PKCS #7: Cryptographic Message Syntax
        Standard.  Version 1.5, November 1993.
   
   [3]  RSA Laboratories. PKCS #9: Selected Attribute Types. Version
        2.0, February 2000.
   
   [4]  Adams, C. and S. Farrell, "Internet X.509 Public Key
        Infrastructure - Certificate Management Protocols", RFC 2510,
        March 1999.
   
   [5]  Kaliski, B., "Privacy Enhancement for Internet Electronic Mail:
        Part IV: Key Certification and Related Services", RFC 1424,
        February 1993.
   
   [6]  Kaliski, B., "PKCS #10: Certification Request Syntax Version
        1.5", RFC 2314, March 1998.
   
   [7]  ITU-T Recommendation X.500 (1997) | ISO/IEC 9594-1:1998,
        Information technology - Open Systems Interconnection - The
        Directory: Overview of concepts, models and services.
   
   [8]  ITU-T Recommendation X.501 (1993) | ISO/IEC 9594-2:1995,
        Information technology - Open Systems Interconnection - The
        Directory: Models.
   
   [9]  ITU-T Recommendation X.509 (1997) | ISO/IEC 9594-8:1998,
        Information technology - Open Systems Interconnection -The
        Directory:  Authentication framework.
   
   [10] ITU-T Recommendation X.680 (1997) | ISO/IEC 8824-1:1998,
        Information Technology - Abstract Syntax Notation One (ASN.1):
        Specification of Basic Notation.
   
   [11] ITU-T Recommendation X.681 (1997) | ISO/IEC 8824-2:1998,
        Information Technology - Abstract Syntax Notation One (ASN.1):
        Information Object Specification.
   
   [12] ITU-T Recommendation X.682 (1997) | ISO/IEC 8824-3:1998,
        Information Technology - Abstract Syntax Notation One (ASN.1):
        Constraint Specification.
   
   [13] ITU-T Recommendation X.683 (1997) | ISO/IEC 8824-4:1998,
        Information Technology - Abstract Syntax Notation One (ASN.1):
        Parameterization of ASN.1 Specifications.
   
   [14] ITU-T Recommendation X.690 (1997) | ISO/IEC 8825-1:1998,
        Information Technology - ASN.1 Encoding Rules: Specification of
        Basic Encoding Rules (BER), Canonical Encoding Rules (CER) and
        Distinguished Encoding Rules (DER).

E. Contact Information & About PKCS

The Public-Key Cryptography Standards are specifications produced by RSA Laboratories in cooperation with secure systems developers worldwide for the purpose of accelerating the deployment of public- key cryptography. First published in 1991 as a result of meetings with a small group of early adopters of public-key technology, the PKCS documents have become widely referenced and implemented. Contributions from the PKCS series have become part of many formal and de facto standards, including ANSI X9 documents, PKIX, SET, S/MIME, and SSL.

Further development of PKCS occurs through mailing list discussions and occasional workshops, and suggestions for improvement are welcome. For more information, contact: 

        PKCS Editor
        RSA Laboratories
        20 Crosby Drive
        Bedford, MA  01730 USA
        pkcs-editor@rsasecurity.com
        http://www.rsasecurity.com/rsalabs/pkcs

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The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. 

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