RFC 5208: Public-Key Cryptography Standards (PKCS) #8: Private-Key Information Syntax Specification Version 1.2

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    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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    RFC 5208    PKCS #8: Private-Key Information Syntax Standard    May 2008

    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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    RFC 5208    PKCS #8: Private-Key Information Syntax Standard    May 2008

    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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    RFC 5208    PKCS #8: Private-Key Information Syntax Standard    May 2008

    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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    RFC 5208    PKCS #8: Private-Key Information Syntax Standard    May 2008

    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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    RFC 5208    PKCS #8: Private-Key Information Syntax Standard    May 2008

    Author's Addresses

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

       EMail: kaliski_burt@emc.com

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    RFC 5208    PKCS #8: Private-Key Information Syntax Standard    May 2008

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