Network Working Group                                       B. Kaliski
Request for Comments: 2314                       RSA Laboratories East
Category: Informational                                     March 1998

                 PKCS #10: Certification Request Syntax
                              Version 1.5

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 (C) The Internet Society (1998).  All Rights Reserved.

Overview

   This document describes a syntax for certification requests.

1. Scope

   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, who transforms the request to an X.509
   public-key certificate, or a PKCS #6 extended certificate. (In what
   form the certification authority returns the newly signed certificate
   is outside the scope of this document. A PKCS #7 message is one
   possibility.)

   The intention of including a set of attributes is twofold: to provide
   other information about a given entity, such as the postal address to
   which the signed certificate should be returned if electronic mail is
   not available, or a "challenge password" by which the entity may
   later request certificate revocation; and to provide attributes for a
   PKCS #6 extended certificate. A non-exhaustive list of attributes is
   given in PKCS #9.

   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 the certification authority.

   The preliminary intended application of this document is to support
   PKCS #7 cryptographic messages, but is expected that other
   applications will be developed.

2. References

   PKCS #1   RSA Laboratories. PKCS #1: RSA Encryption
             Standard. Version 1.5, November 1993.

   PKCS #6   RSA Laboratories. PKCS #6: Extended-Certificate
             Syntax. Version 1.5, November 1993.

   PKCS #7   RSA Laboratories. PKCS #7: Cryptographic Message
             Syntax. Version 1.5, November 1993.

   PKCS #9   RSA Laboratories. PKCS #9: Selected Attribute
             Types. Version 1.1, November 1993.

   RFC 1424  Kaliski, B., "Privacy Enhancement for
             Internet Electronic Mail: Part IV: Key
             Certification and Related Services," RFC 1424,
             February 1993.

   X.208     CCITT. Recommendation X.208: Specification of
             Abstract Syntax Notation One (ASN.1). 1988.

   X.209     CCITT. Recommendation X.209: Specification of
             Basic Encoding Rules for Abstract Syntax Notation
             One (ASN.1). 1988.

   X.500     CCITT. Recommendation X.500: The Directory--
             Overview of Concepts, Models and
             Services. 1988.

   X.501     CCITT. Recommendation X.501: The Directory--
             Models. 1988.

   X.509     CCITT. Recommendation X.509: The Directory--
             Authentication Framework. 1988.

3. Definitions

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

   AlgorithmIdentifier: A type that identifies an algorithm (by object
   identifier) and any associated parameters. This type is defined in
   X.509.

   Attribute: A type that contains an attribute type (specified by
   object identifier) and one or more attribute values. This type is
   defined in X.501.

   ASN.1: Abstract Syntax Notation One, as defined in X.208.

   BER: Basic Encoding Rules, as defined in X.209.

   Certificate: A type that binds an 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, and a validity period.

   DER: Distinguished Encoding Rules for ASN.1, as defined in X.509,
   Section 8.7.

   Name: A type that uniquely identifies or "distinguishes" objects in a
   X.500 directory. This type is defined in X.501.  In an X.509
   certificate, the type identifies the certificate issuer and the
   entity whose public key is certified.

4. Symbols and abbreviations

   No symbols or abbreviations are defined in this document.

5. General overview

   The next section specifies certification request syntax.

   This document exports one type, CertificationRequest.

6. Certification request syntax

   This section gives the syntax for certification requests.

   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
             distinguished name, a public key, and optionally a set of
             attributes is constructed by an entity.

        2.   The CertificationRequestInfo value is signed with
             the entity's private key. (See Section 6.2.)

        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 verifying the
   entity's signature, and, if it is valid, constructing a X.509
   certificate from the distinguished name and public key, as well as an
   issuer name, serial number, validity period, and signature algorithm
   of the certification authority's choice. If the certification request
   contains a PKCS #9 extended-certificate-attributes attribute, the
   certification authority also constructs a PKCS #6 extended
   certificate from the X.509 certificate and the extended-certificate-
   attributes attribute value.

   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.

   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.

   Notes.

        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.

        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.

        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.

        4.   This document is not compatible with the
             certification request syntax for Privacy-Enhanced Mail, as
             described in RFC 1424. The syntax in this document 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. The syntax in this document is designed to minimize
             request size, an important constraint for those
             certification authorities accepting requests on paper.

6.1 CertificationRequestInfo

   Certification request information shall have ASN.1 type
   CertificationRequestInfo:

   CertificationRequestInfo ::= SEQUENCE {
     version Version,
     subject Name,
     subjectPublicKeyInfo SubjectPublicKeyInfo,
     attributes [0] IMPLICIT Attributes }

   Version ::= INTEGER

   Attributes ::= SET OF Attribute

   The fields of type CertificationRequestInfo have the following
   meanings:

        o    version is the version number, for compatibility
             with future revisions of this document. It shall be 0 for
             this version of the document.

        o    subject is the distinguished name of the
             certificate subject (the entity whose public key is to be
             certified).

        o    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
             X.509's rsa and PKCS #1's rsaEncryption. The information
             also includes a bit-string representation of the entity's
             public key.  For both public-key algorithms just mentioned,
             the bit string contains the BER encoding of a value of
             X.509/PKCS #1 type RSAPublicKey.

        o    attributes is a set 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 that the certificate revocation. Another
             example is the extended-certificate-attributes attribute,
             which specifies attributes for a PKCS #6 extended
             certificate.

6.2 CertificationRequest

   A certification request shall have ASN.1 type CertificationRequest:

   CertificationRequest ::= SEQUENCE {
     certificationRequestInfo CertificationRequestInfo,
     signatureAlgorithm SignatureAlgorithmIdentifier,
     signature Signature }

   SignatureAlgorithmIdentifier ::= AlgorithmIdentifier

   Signature ::= BIT STRING

   The fields of type CertificationRequest have the following meanings:

        o    certificateRequestInfo is the "certification
             request information." It is the value being
             signed.

        o    signatureAlgorithm identifies the signature
             algorithm (and any associated parameters) under
             which the certification-request information is
             signed. Examples include PKCS #1's
             md2WithRSAEncryption and md5WithRSAEncryption.

        o    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 field 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. The syntax for CertificationRequest could equivalently be
   written with the X.509 SIGNED macro:

   CertificationRequest ::= SIGNED CertificateRequestInfo

Security Considerations

   Security issues are discussed throughout this memo.

Revision history

   Version 1.0

   Version 1.0 is the initial version.

Acknowledgements

   This document is based on a contribution of RSA Laboratories, a
   division of RSA Data Security, Inc.  Any substantial use of the text
   from this document must acknowledge RSA Data Security, Inc. RSA Data
   Security, Inc.  requests that all material mentioning or referencing
   this document identify this as "RSA Data Security, Inc. PKCS #10".

Author's Address

   Burt Kaliski
   RSA Laboratories East
   20 Crosby Drive
   Bedford, MA  01730

   Phone: (617) 687-7000
   EMail: burt@rsa.com

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