Network Working Group                                         B. Kaliski
Request for Comments: 5208                                           EMC
Category: Informational                                         May 2008


            Public-Key Cryptography Standards (PKCS) #8:
       Private-Key Information Syntax Specification Version 1.2

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.

IESG Note

  The IESG thanks RSA Laboratories for transferring change control to
  the IETF.  Enhancements to this specification that preserve backward
  compatibility are expected in an upcoming IETF standards track
  document.

Abstract

  This document represents a republication of PKCS #8 v1.2 from RSA
  Laboratories' Public Key Cryptography Standard (PKCS) series.  Change
  control is transferred to the IETF.  The body of this document,
  except for the security considerations section, is taken directly
  from the PKCS #8 v1.2 specification.

  This document describes a syntax for private-key information.

Table of Contents

  1. Introduction ....................................................2
  2. Definitions .....................................................2
  3. Symbols and Abbreviations .......................................2
  4. General Overview ................................................2
  5. Private-Key Information Syntax ..................................3
  6. Encrypted Private-Key Information Syntax ........................4
  7. Security Considerations .........................................4
  Appendix A. ASN.1 Syntax ...........................................5
  Informative References .............................................6









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1.  Introduction

  This document describes a syntax for private-key information.
  Private-key information includes a private key for some public-key
  algorithm and a set of attributes.  The document also describes a
  syntax for encrypted private keys.  A password-based encryption
  algorithm (e.g., one of those described in [PKCS#5]) could be used to
  encrypt the private-key information.

  The intention of including a set of attributes is to provide a simple
  way for a user to establish trust in information such as a
  distinguished name or a top-level certification authority's public
  key.  While such trust could also be established with a digital
  signature, encryption with a secret key known only to the user is
  just as effective and possibly easier to implement.  A non-exhaustive
  list of attributes is given in [PKCS#9].

2.  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].

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

     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].

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

3.  Symbols and Abbreviations

  No symbols or abbreviations are defined in this document.

4.  General Overview

  The next two sections specify private-key information syntax and
  encrypted private-key information syntax.

  This document exports two types: PrivateKeyInfo (Section 6) and
  EncryptedPrivateKeyInfo (Section 7).







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5.  Private-Key Information Syntax

  This section gives the syntax for private-key information.

  Private-key information shall have ASN.1 type PrivateKeyInfo:

     PrivateKeyInfo ::= SEQUENCE {
       version                   Version,
       privateKeyAlgorithm       PrivateKeyAlgorithmIdentifier,
       privateKey                PrivateKey,
       attributes           [0]  IMPLICIT Attributes OPTIONAL }

     Version ::= INTEGER

     PrivateKeyAlgorithmIdentifier ::= AlgorithmIdentifier

     PrivateKey ::= OCTET STRING

     Attributes ::= SET OF Attribute

  The fields of type PrivateKeyInfo have the following meanings:

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

     privateKeyAlgorithm identifies the private-key algorithm.  One
     example of a private-key algorithm is PKCS #1's rsaEncryption
     [PKCS#1].

     privateKey is an octet string whose contents are the value of the
     private key.  The interpretation of the contents is defined in the
     registration of the private-key algorithm.  For an RSA private
     key, for example, the contents are a BER encoding of a value of
     type RSAPrivateKey.

     attributes is a set of attributes.  These are the extended
     information that is encrypted along with the private-key
     information.












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6.  Encrypted Private-Key Information Syntax

  This section gives the syntax for encrypted private-key information.

  Encrypted private-key information shall have ASN.1 type
  EncryptedPrivateKeyInfo:

     EncryptedPrivateKeyInfo ::= SEQUENCE {
       encryptionAlgorithm  EncryptionAlgorithmIdentifier,
       encryptedData        EncryptedData }

     EncryptionAlgorithmIdentifier ::= AlgorithmIdentifier

     EncryptedData ::= OCTET STRING

  The fields of type EncryptedPrivateKeyInfo have the following
  meanings:

     encryptionAlgorithm identifies the algorithm under which the
     private-key information is encrypted.  Two examples are PKCS #5's
     pbeWithMD2AndDES-CBC and pbeWithMD5AndDES-CBC [PKCS#5].

     encryptedData is the result of encrypting the private-key
     information.

  The encryption process involves the following two steps:

     1. The private-key information is BER encoded, yielding an octet
        string.

     2. The result of step 1 is encrypted with the secret key to give
        an octet string, the result of the encryption process.

7.  Security Considerations

  Protection of the private-key information is vital to public-key
  cryptography.  Disclosure of the private-key material to another
  entity can lead to masquerades.  The encryption algorithm used in the
  encryption process must be as 'strong' as the key it is protecting.












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Appendix A.  ASN.1 Syntax

PKCS-8 {iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs-8(8)
        modules(1) pkcs-8(1)}

-- $Revision: 1.5 $

-- This module has been checked for conformance with the ASN.1
-- standard by the OSS ASN.1 Tools

DEFINITIONS IMPLICIT TAGS ::=

BEGIN

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

IMPORTS

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

Attribute
        FROM InformationFramework informationFramework

AlgorithmIdentifier, ALGORITHM-IDENTIFIER
        FROM PKCS-5 {iso(1) member-body(2) us(840) rsadsi(113549)
        pkcs(1) pkcs-5(5) modules(16) pkcs-5(1)};

-- Private-key information syntax

PrivateKeyInfo ::= SEQUENCE {
  version Version,
  privateKeyAlgorithm AlgorithmIdentifier {{PrivateKeyAlgorithms}},
  privateKey PrivateKey,
  attributes [0] Attributes OPTIONAL }

Version ::= INTEGER {v1(0)} (v1,...)

PrivateKey ::= OCTET STRING

Attributes ::= SET OF Attribute







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-- Encrypted private-key information syntax

EncryptedPrivateKeyInfo ::= SEQUENCE {
   encryptionAlgorithm AlgorithmIdentifier {{KeyEncryptionAlgorithms}},
   encryptedData EncryptedData
}

EncryptedData ::= OCTET STRING

PrivateKeyAlgorithms ALGORITHM-IDENTIFIER ::= {
    ... -- For local profiles
}

KeyEncryptionAlgorithms ALGORITHM-IDENTIFIER ::= {
    ... -- For local profiles
}

END

Informative References

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

  [PKCS#5]  RSA Laboratories. PKCS #5: Password-Based Encryption
            Standard. Version 1.5, November 1993.

  [PKCS#9]  RSA Laboratories. PKCS #9: Selected Attribute Types.
            Version 1.1, November 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.501]   CCITT. Recommendation X.501: The Directory - Models. 1988.

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










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Author's Addresses

  Burt Kaliski
  EMC Corporation
  176 South Street
  Hopkinton, MA  01748
  USA

  EMail: [email protected]










































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