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Versions: 00 01 02 03 RFC 4055

PKIX Working Group             J. Schaad (Soaring Hawk Consulting)
Internet Draft                       B. Kaliski (RSA Laboratories)
                                       R. Housley (Vigil Security)
expires September 2004                                  March 2004

       Additional Algorithms and Identifiers for RSA Cryptography
        for use in the Internet X.509 Public Key Infrastructure
       Certificate and Certificate Revocation List (CRL) Profile
                  <draft-ietf-pkix-rsa-pkalgs-03.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 groups may also
   distribute working documents as Internet-Drafts.

   Internet-Drafts are draft documents valid for a maximum of six
   months and may be updated, replaced, or obsoleted by other documents
   at any time.  It is inappropriate to use Internet-Drafts as
   reference material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Drafts Shadow Directories can be accessed at
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Abstract

   This document supplements RFC 3279.  It describes the conventions
   for using the RSASSA-PSS signature algorithm, the RSAES-OAEP key
   transport algorithm and additional one-way hash functions with the
   PKCS #1 version 1.5 signature algorithm in the Internet X.509 Public
   Key Infrastructure (PKI).  Encoding formats, algorithm identifiers,
   and parameter formats are specified.

Table of Contents

1  Introduction.......................................................2
 1.1  Terminology....................................................2
 1.2  RSA Public Keys................................................2
2  Common Functions...................................................5
 2.1  One-way Hash Functions.........................................5
 2.2  Mask Generation Functions......................................6
3  RSASSA-PSS Signature Algorithm.....................................7
 3.1  RSASSA-PSS Public Keys.........................................7
 3.2  RSASSA-PSS Signature Values....................................9
 3.3  RSASSA-PSS Signature Parameter Validation......................9
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4  RSAES-OAEP Key Transport Algorithm................................10
 4.1  RSAES-OAEP Public Keys........................................10
5  PKCS #1 Version 1.5 Signature Algorithm...........................12
6  ASN.1 Module......................................................13
7  References........................................................19
 7.1  Normative References..........................................19
 7.2  Informative References........................................19
8  Security Considerations...........................................20
10  Author Addresses.................................................22
11  Full Copyright Statement.........................................22



1  Introduction

   This document supplements RFC 3279 [PKALGS].  This document
   describes the conventions for using the RSASSA-PSS signature
   algorithm and the RSAES-OAEP key transport algorithm in the Internet
   X.509 Public Key Infrastructure (PKI) [PROFILE].  Both of these RSA-
   based algorithms are specified in [P1v2.1].  The algorithm
   identifiers and associated parameters for subject public keys that
   employ either of these algorithms are specified, and the encoding
   format for RSASSA-PSS signatures is specified.  Also, the algorithm
   identifiers for using the SHA-224, SHA-256, SHA-384, and SHA-512
   one-way hash functions with the PKCS #1 version 1.5 signature
   algorithm [P1v1.5] are specified.

   This specification supplements RFC 3280 [PROFILE], which profiles
   the X.509 Certificates and Certificate Revocation Lists (CRLs) for
   use in the Internet.  This specification extends the list of
   algorithms discussed in RFC 3279 [PKALGS].  The X.509 Certificate
   and CRL definitions use ASN.1 [X.208-88], the Basic Encoding Rules
   (BER) [X.209-88], and the Distinguished Encoding Rules (DER) [X.509-
   88].

   This specification defines the contents of the signatureAlgorithm,
   signatureValue, signature, and subjectPublicKeyInfo fields within
   Internet X.509 certificates and CRLs.  For each algorithm, the
   appropriate alternatives for the keyUsage extension are provided.


1.1  Terminology

   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 [STDWORDS].


1.2  RSA Public Keys

   RFC 3280 [PROFILE] specifies the profile for using X.509
   Certificates in Internet applications.  When a RSA public key will
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   be used for RSASSA-PSS digital signatures or RSAES-OAEP key
   transport, the conventions specified in this section augment RFC
   3280.

   Traditionally, the rsaEncryption object identifier is used to
   identify RSA public keys.  However, to implement all of the
   recommendations described in the Security Considerations section of
   this document (see section 8), the certificate user needs to be able
   to determine the form of digital signature or key transport that the
   RSA private key owner associates with the public key.

   The rsaEncryption object identifier continues to identify the
   subject public key when the RSA private key owner does not wish to
   limit the use of the public key exclusively to either RSASSA-PSS or
   RSAES-OAEP.  In this case, the rsaEncryption object identifier MUST
   be used in the algorithm field within the subject public key
   information, and the parameters field MUST contain NULL.

      rsaEncryption  OBJECT IDENTIFIER  ::=  { pkcs-1 1 }

   Further discussion of the conventions associated with use of the
   rsaEncryption object identifier can be found in RFC 3279 (see
   [PKALGS], section 2.3.1).

   When the RSA private key owner wishes to limit the use of the public
   key exclusively to RSASSA-PSS, then the id-RSASSA-PSS object
   identifier MUST be used in the algorithm field within the subject
   public key information, and, if present, the parameters field MUST
   contain RSASSA-PSS-params.  The id-RSASSA-PSS object identifier
   value and the RSASSA-PSS-params syntax are fully described in
   section 3 of this document.

   When the RSA private key owner wishes to limit the use of the public
   key exclusively to RSAES-OAEP, then the id-RSAES-OAEP object
   identifier MUST be used in the algorithm field within the subject
   public key information, and, if present, the parameters field MUST
   contain RSAES-OAEP-params.  The id-RSAES-OAEP object identifier
   value and the RSAES-OAEP-params syntax are fully described in
   section 4 of this document.

   Note: It is not possible to restrict the use of a key to only just
   two of the algorithms (i.e. RSASSA-PSS and RSAES-OAEP) in this
   document.

   Regardless of the object identifier used, the RSA public key is
   encoded in the same manner in the subject public key information.
   The RSA public key MUST be encoded using the type RSAPublicKey type:

      RSAPublicKey  ::=  SEQUENCE  {
         modulus            INTEGER,    -- n
         publicExponent     INTEGER  }  -- e


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   Here, the modulus is the modulus n, and publicExponent is the public
   exponent e.  The DER encoded RSAPublicKey is carried in the
   subjectPublicKey BIT STRING within the subject public key
   information.

   The intended application for the key MAY be indicated in the key
   usage certificate extension (see [PROFILE], section 4.2.1.3).

   If the keyUsage extension is present in an end entity certificate
   that conveys an RSA public key with the id-RSASSA-PSS object
   identifier, then the key usage extension MUST contain one or both of
   the following values:

      nonRepudiation; and
      digitalSignature.

   If the keyUsage extension is present in a certification authority
   certificate that conveys an RSA public key with the id-RSASSA-PSS
   object identifier, then the key usage extension MUST contain one or
   more of the following values:

      nonRepudiation;
      digitalSignature;
      keyCertSign; and
      cRLSign.

   When a certificate that conveys an RSA public key with the id-
   RSASSA-PSS object identifier, the certificate user MUST only use the
   certified RSA public key for RSASSA-PSS operations, and, if RSASSA-
   PSS-params is present, the certificate user MUST perform those
   operations using the one-way hash function, mask generation
   function, and trailer field identified in the subject public key
   algorithm identifier parameters within the certificate.

   If the keyUsage extension is present in a certificate that conveys
   an RSA public key with the id-RSAES-OAEP object identifier, then the
   key usage extension MUST contain only the following values:

      keyEncipherment; and
      dataEncipherment.

   However, both keyEncipherment and dataEncipherment SHOULD NOT be
   present.

   When a certificate that conveys an RSA public key with the id-RSAES-
   OAEP object identifier, the certificate user MUST only use the
   certified RSA public key for RSAES-OAEP operations, and, if RSAES-
   OAEP-params is present, the certificate user MUST perform those
   operations using the one-way hash function and mask generation



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   function identified in the subject public key algorithm identifier
   parameters within the certificate.



2  Common Functions

   The RSASSA-PSS signature algorithm and the RSAES-OAEP key transport
   algorithm make use of one-way hash functions and mask generation
   functions.


2.1  One-way Hash Functions

   PKCS #1 version 2.1 [P1v2.1] supports four one-way hash functions
   for use with the RSASSA-PSS signature algorithm and the RSAES-OAEP
   key transport algorithm: SHA-1, SHA-256, SHA-384, and SHA-512
   [SHA2].  This document adds additional support for SHA-224 [SHA-224]
   with both the RSASSA-PSS and the RSAES-OAEP algorithms.  While
   support for additional one-way hash functions could be added in the
   future, no other one-way hash functions are supported by this
   specification.

   These one-way hash functions are identified by the following object
   identifiers:

      id-sha1  OBJECT IDENTIFIER  ::=  { iso(1)
                           identified-organization(3) oiw(14)
                           secsig(3) algorithms(2) 26 }
      id-sha224  OBJECT IDENTIFIER  ::=  {{ joint-iso-itu-t(2)
                           country(16) us(840) organization(1) gov(101)
                           csor(3) nistalgorithm(4) hashalgs(2) 4 }
      id-sha256  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
                           country(16) us(840) organization(1) gov(101)
                           csor(3) nistalgorithm(4) hashalgs(2) 1 }
      id-sha384  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
                           country(16) us(840) organization(1) gov(101)
                           csor(3) nistalgorithm(4) hashalgs(2) 2 }
      id-sha512  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
                           country(16) us(840) organization(1) gov(101)
                           csor(3) nistalgorithm(4) hashalgs(2) 3 }

   There are two possible encodings for the AlgorithmIdentifier
   parameters field associated with these object identifiers.  The two
   alternatives arise from the fact that when the 1988 syntax for
   AlgorithmIdentifier was translated into the 1997 syntax the OPTIONAL
   associated with the algorithm identifier parameters got lost.  Later
   the OPTIONAL was recovered via a defect report, but by then many
   people thought that algorithm parameters were mandatory.  Because of
   this history some implementations encode parameters as a NULL
   element and others omit them entirely.  The correct encoding is to
   omit the parameters field; however, at the time that RSASSA-PSS and


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   RSAES-OAEP were defined it was done using the NULL parameters rather
   than absent parameters.

   All implementations MUST accept both NULL and absent parameters as
   legal and equivalent encodings.

   To be clear, the following algorithm identifiers are used when a
   NULL parameter MUST be present:

      sha1Identifier  AlgorithmIdentifier  ::=  { id-sha1, NULL }

      sha224Identifier  AlgorithmIdentifier  ::=  { id-sha224, NULL }
      sha256Identifier  AlgorithmIdentifier  ::=  { id-sha256, NULL }
      sha384Identifier  AlgorithmIdentifier  ::=  { id-sha384, NULL }
      sha512Identifier  AlgorithmIdentifier  ::=  { id-sha512, NULL }


2.2  Mask Generation Functions

   One mask generation function is used with the RSASSA-PSS signature
   algorithm and the RSAES-OAEP key transport algorithm: MGF1 [P1v2.1].
   No other mask generation functions are supported by this
   specification.

   MGF1 is identified by the following object identifier:

      id-mgf1  OBJECT IDENTIFIER  ::=  { pkcs-1 8 }

   The parameters field associated with id-mgf1 MUST have a
   hashAlgorithm value, which identifies the hash function being used
   with MGF1.  This value MUST be sha1Identifier, sha224Identifier,
   sha256Identifier, sha384Identifier, or sha512Identifier, as
   specified in section 2.1.  Implementations MUST support the default
   value, sha1Identifier, and implementations MAY support the other
   four values.

   The following algorithm identifiers have been assigned for each of
   these alternatives:

      mgf1SHA1Identifier  AlgorithmIdentifier  ::=
                           { id-mgf1, sha1Identifier }
      mgf1SHA224Identifier  AlgorithmIdentifier  ::=
                           { id-mgf1, sha224Identifier }
      mgf1SHA256Identifier  AlgorithmIdentifier  ::=
                           { id-mgf1, sha256Identifier }
      mgf1SHA384Identifier  AlgorithmIdentifier  ::=
                           { id-mgf1, sha384Identifier }
      mgf1SHA512Identifier  AlgorithmIdentifier  ::=
                           { id-mgf1, sha512Identifier }




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3  RSASSA-PSS Signature Algorithm

   This section describes the conventions for using the RSASSA-PSS
   signature algorithm with the Internet X.509 certificate and CRL
   profile [PROFILE].  The RSASSA-PSS signature algorithm is specified
   in PKCS #1 version 2.1 [P1v2.1].  The five one-way hash functions
   discussed in section 2.1 and the one mask generation function
   discussed in section 2.2 can be used with RSASSA-PSS.

   CAs that issue certificates with the id-RSASSA-PSS algorithm
   identifier SHOULD require that the parameters be present in the
   publicKeyAlgorithms field if the cA boolean flag is set in the basic
   constraints extension.  CAs MAY require that the parameters be
   present in the publicKeyAlgorithms field for end-entity
   certificates.

   CAs that use the RSASSA-PSS algorithm for signing certificates,
   SHOULD have RSASSA-PSS-params the parameters present in their own
   certificates.  CAs that use the RSASSA-PSS algorithm for signing,
   certificates and CRLs MUST include RSASSA-PSS-params the parameters
   in the signature algorithm field of the TBSCertificate and
   TBSCertList structures.

   Entities that validate RSASSA-PSS signatures MUST have support for
   SHA-1.  They MAY also support the other hashing algorithms in
   section 2.1.

   The data to be signed (e.g., the one-way hash function output value)
   is formatted for the signature algorithm to be used.  Then, a
   private key operation (e.g., RSA encryption) is performed to
   generate the signature value.  This signature value is then ASN.1
   encoded as a BIT STRING and included in the Certificate or
   CertificateList in the signature field.  Section 3.2 specifies the
   format of RSASSA-PSS signature values.


3.1  RSASSA-PSS Public Keys

   When RSASSA-PSS is used in an AlgorithmIdentifier,the parameters
   MUST employ the RSASSA-PSS-params syntax.  The parameters may be
   either absent or present when used as subject public key
   information.  The parameters MUST be present when used in the
   algorithm identifier associated with for a signature value.

   When signing, it is RECOMMENDED that, except for saltLength, the
   parameters remain fixed for all usages of a given RSA key pair.

      id-RSASSA-PSS  OBJECT IDENTIFIER  ::=  { pkcs-1 10 }

      RSASSA-PSS-params  ::=  SEQUENCE  {
         hashAlgorithm      [0] HashAlgorithm DEFAULT
                                   sha1Identifier,
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         maskGenAlgorithm   [1] MaskGenAlgorithm DEFAULT
                                   mgf1SHA1Identifier,
         saltLength         [2] INTEGER DEFAULT 20,
         trailerField       [3] INTEGER DEFAULT 1  }

   The fields of type RSASSA-PSS-params have the following meanings:

      hashAlgorithm

         The hashAlgorithm field identifies the hash function.  It MUST
         be one of the algorithm identifiers listed in section 2.1, and
         the default hash function is SHA-1.  Implementations MUST
         support SHA-1, and implementations MAY support other one-way
         hash functions listed in section 2.1.  Implementations that
         perform signature generation MUST omit the hashAlgorithm field
         when SHA-1 is used, indicating that the default algorithm was
         used.  Implementations that perform signature validation MUST
         recognize both the id-sha1 object identifier and an absent
         hashAlgorithm field as an indication that SHA-1 was used.

      maskGenAlgorithm

         The maskGenAlgorithm field identifies the mask generation
         function.  The default mask generation function is MGF1 with
         SHA-1.  For MGF1, it is strongly RECOMMENDED that the
         underlying hash function be the same as the one identified by
         hashAlgorithm.  Implementations MUST support MGF1.  MGF1
         requires a one-way hash function, and it is identified in the
         parameters field of the MGF1 algorithm identifier.
         Implementations MUST support SHA-1, and implementations MAY
         support other one-way hash functions listed in section 2.1.
         The MGF1 algorithm identifier is comprised of the id-mgf1
         object identifier and a parameter that contains the algorithm
         identifier of the one-way hash function employed with MGF1.
         The SHA-1 algorithm identifier is comprised of the id-sha1
         object identifier and an (optional) parameter of NULL.
         Implementations that perform signature generation MUST omit
         the maskGenAlgorithm field when MGF1 with SHA-1 is used,
         indicating that the default algorithm was used.

         Although mfg1SHA1Identifier is defined as the default value
         for this field, implementations MUST accept both the default
         value encoding (i.e. an absent field) and mfg1SHA1Identifier
         to be explicitly present in the encoding.

      saltLength

         The saltLength field is the octet length of the salt.  For a
         given hashAlgorithm, the minimum value of saltLength is the
         number of octets in the hash value.  Unlike the other fields
         of type RSASSA-PSS-params, saltLength does not need to be


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         fixed for a given RSA key pair; a different value could be
         used for each RSASSA-PSS signature generated.

      trailerField

         The trailerField field is an integer.  It provides
         compatibility with the draft IEEE P1363a [P1363a].  The value
         MUST be 1, which represents the trailer field with hexadecimal
         value 0xBC.  Other trailer fields, including the trailer field
         composed of HashID concatenated with 0xCC that is specified in
         IEEE P1363a, are not supported.  Implementations that perform
         signature generation MUST omit the trailerField field,
         indicating that the default trailer field value was used.
         Implementations that perform signature validation MUST
         recognize both a present trailerField field with value 1 and
         an absent trailerField field.

   If the default values of the hashAlgorithm, maskGenAlgorithm, and
   trailerField fields of RSASSA-PSS-params are used, then the
   algorithm identifier will have the following value:

      rSASSA-PSS-Default-Identifier  AlgorithmIdentifier  ::=  {
                           id-RSASSA-PSS, rSASSA-PSS-Default-Params }

      rSASSA-PSS-Default-Params RSASSA-PSS-Params ::= {
                           sha1Identifier, mgf1SHA1Identifier, 20, 1}


3.2  RSASSA-PSS Signature Values

   The output of the RSASSA-PSS signature algorithm is an octet string,
   which has the same length in octets as the RSA modulus n.

   Signature values in CMS [CMS] are represented as octet strings, and
   the output is used directly.  However, signature values in
   certificates and CRLs [PROFILE] are represented as bit strings, and
   conversion is needed.

   To convert a signature value to a bit string, the most significant
   bit of the first octet of the signature value SHALL become the first
   bit of the bit string, and so on through the least significant bit
   of the last octet of the signature value, which SHALL become the
   last bit of the bit string.


3.3  RSASSA-PSS Signature Parameter Validation

   Three possible parameter validation scenarios exist for RSASSA-PSS
   signature values.

   1. The key is identified by the rsaEncryption algorithm identifier.
   In this case no parameter validation is needed.

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   2. The key is identified by the id-RSASSA-PSS signature algorithm
   identifier, but the parameters field is absent.  In this case no
   parameter validation is needed.

   3. The key is identified by the id-RSASSA-PSS signature algorithm
   identifier and the parameters are present.  In this case all
   parameters in the signature structure algorithm identifier MUST
   match the parameters in the key structure algorithm identifier
   except the saltLength field.  The saltLength field in the signature
   parameters MUST be greater or equal to that in the key parameters
   field.


4  RSAES-OAEP Key Transport Algorithm

   This section describes the conventions for using the RSAES-OAEP key
   transport algorithm with the Internet X.509 certificate and CRL
   profile [PROFILE].  RSAES-OAEP is specified in PKCS #1 version 2.1
   [P1v2.1].  The five one-way hash functions discussed in section 2.1
   and the one mask generation function discussed in section 2.2 can be
   used with RSAES-OAEP.  Conforming CAs and applications MUST support
   RSAES-OAEP key transport algorithm using SHA-1.  The other three
   one-way hash functions MAY also be supported.

   CAs that issue certificates with the id-RSAES-OAEP algorithm
   identifier SHOULD require that the parameters be present in the
   publicKeyAlgorithms field for all certificates.
   Entities that use a certificate with a publicKeyAlgorithm value of
   id-RSA-OAEP where the parameters are absent SHOULD use the default
   set of parameters for RSAES-OAEP-params.  Entities that use a
   certificate with a publicKeyAlgorithm value of rsaEncryption SHOULD
   use the default set of parameters for RSAES-OAEP-params


4.1  RSAES-OAEP Public Keys

   When id-RSAES-OAEP is used in an AlgorithmIdentifier, the parameters
   MUST employ the RSAES-OAEP-params syntax.  The parameters may be
   either absent or present when used as subject public key
   information.  The parameters MUST be present when used in the
   algorithm identifier associated with an encryption value.

      id-RSAES-OAEP  OBJECT IDENTIFIER  ::=  { pkcs-1 7 }

      RSAES-OAEP-params  ::=  SEQUENCE  {
         hashFunc          [0] AlgorithmIdentifier DEFAULT
                                  sha1Identifier,
         maskGenFunc       [1] AlgorithmIdentifier DEFAULT

                                  mgf1SHA1Identifier,
         pSourceFunc       [2] AlgorithmIdentifier DEFAULT
                                  pSpecifiedEmptyIdentifier  }

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      pSpecifiedEmptyIdentifier  AlgorithmIdentifier  ::=
                           { id-pSpecified, nullOctetString }

      nullOctetString  OCTET STRING (SIZE (0))  ::=  { ''H }

   The fields of type RSAES-OAEP-params have the following meanings:

      hashFunc

         The hashFunc field identifies the one-way hash function.  It
         MUST be one of the algorithm identifiers listed in section
         2.1, and the default hash function is SHA-1.  Implementations
         MUST support SHA-1, and implementations MAY support other one-
         way hash functions listed in section 2.1.  Implementations
         that perform encryption MUST omit the hashFunc field when SHA-
         1 is used, indicating that the default algorithm was used.
         Implementations that perform decryption MUST recognize both
         the id-sha1 object identifier and an absent hashFunc field as
         an indication that SHA-1 was used.

      maskGenFunc

         The maskGenFunc field identifies the mask generation function.
         The default mask generation function is MGF1 with SHA-1.  For
         MGF1, it is strongly RECOMMENDED that the underlying hash
         function be the same as the one identified by hashFunc.
         Implementations MUST support MGF1.  MGF1 requires a one-way
         hash function, and it is identified in the parameter field of
         the MGF1 algorithm identifier.  Implementations MUST support
         SHA-1, and implementations MAY support other one-way hash
         functions listed in section 2.1.  The MGF1 algorithm
         identifier is comprised of the id-mgf1 object identifier and a
         parameter that contains the algorithm identifier of the one-
         way hash function employed with MGF1.  The SHA-1 algorithm
         identifier is comprised of the id-sha1 object identifier and
         an (optional) parameter of NULL.  Implementations that perform
         encryption MUST omit the maskGenFunc field when MGF1 with SHA-
         1 is used, indicating that the default algorithm was used.

         Although mfg1SHA1Identifier is defined as the default value
         for this field, implementations MUST accept both the default
         value encoding (i.e. an absent field) and the
         mfg1SHA1Identifier to be explicitly present in the encoding.

      pSourceFunc

         The pSourceFunc field identifies the source (and possibly the
         value) of the encoding parameters, commonly called P.
         Implementations MUST represent P by an algorithm identifier,
         id-pSpecified, indicating that P is explicitly provided as an
         OCTET STRING in the parameters.  The default value for P is an


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         empty string.  In this case, pHash in EME-OAEP contains the
         hash of a zero length string.  Implementations MUST support a
         zero length P value.  Implementations that perform encryption
         MUST omit the pSourceFunc field when a zero length P value is
         used, indicating that the default value was used.
         Implementations that perform decryption MUST recognize both
         the id-pSpecified object identifier and an absent pSourceFunc
         field as an indication that a zero length P value was used.
         Implementations that perform decryption MUST support a zero
         length P value, and they MAY support other values.  Compliant
         implementations MUST NOT use any value other than id-
         pSpecifieid for pSourceFunc.

   If the default values of the hashFunc, maskGenFunc, and pSourceFunc
   fields of RSAES-OAEP-params are used, then the algorithm identifier
   will have the following value:

      rSAES-OAEP-Default-Identifier  AlgorithmIdentifier  ::=
                            { id-RSAES-OAEP,
                              rSAES-OAEP-Default-Params }

      rSAES-OAEP-Default-Params RSASSA-OAEP-params ::=
                               { sha1Identifier,
                                 mgf1SHA1Identifier,
                                 pSpecifiedEmptyIdentifier  }



5  PKCS #1 Version 1.5 Signature Algorithm

   RFC 2313 [P1v1.5] specifies the PKCS #1 Version 1.5 signature
   algorithm.  This specification is also included in PKCS #1 Version
   2.1 [P1v2.1].  RFC 3279 [PKALGS] specifies the use of the PKCS #1
   Version 1.5 signature algorithm with the MD2, MD5, and the SHA-1
   one-way hash functions.  This section specifies the algorithm
   identifiers for using the SHA-224, SHA-256, SHA-384, and SHA-512
   one-way hash functions with the PKCS #1 version 1.5 signature
   algorithm.

   The RSASSA-PSS signature algorithm is preferred over the PKCS #1
   Version 1.5 signature algorithm.  Although no attacks are known
   against PKCS #1 Version 1.5 signature algorithm, in the interest of
   increased robustness, RSASSA-PSS signature algorithm is recommended
   for eventual adoption, especially by new applications.  This section
   is included for compatibility with existing applications, and while
   still appropriate for new applications, a gradual transition to the
   RSASSA-PSS signature algorithm is encouraged.

   The PKCS #1 Version 1.5 signature algorithm with these one-way hash
   functions and the RSA encryption algorithm is implemented using the
   padding and encoding conventions described in RFC 2313 [P1v1.5].


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   The message digest is computed using the SHA-224, SHA-256, SHA-384,
   or SHA-512 one-way hash function.

   The PKCS #1 version 1.5 signature algorithm, as specified in RFC
   2313 includes a data encoding step.  In this step, the message
   digest and the object identifier for the one-way hash function used
   to compute the message digest are combined.  When performing the
   data encoding step, the id-sha224, id-sha256, id-sha384, and id-
   sha512 object identifiers (see section 2.1) MUST be used to specify
   the SHA-224, SHA-256, SHA-384, and SHA-512 one-way hash functions,
   respectively.

   The object identifier used to identify the PKCS #1 version 1.5
   signature algorithm with SHA-224 is:

      sha224WithRSAEncryption  OBJECT IDENTIFIER  ::=  { pkcs-1 14 }

   The object identifier used to identify the PKCS #1 version 1.5
   signature algorithm with SHA-256 is:

      sha256WithRSAEncryption  OBJECT IDENTIFIER  ::=  { pkcs-1 11 }

   The object identifier used to identify the PKCS #1 version 1.5
   signature algorithm with SHA-384 is:

      sha384WithRSAEncryption  OBJECT IDENTIFIER  ::=  { pkcs-1 12 }

   The object identifier used to identify the PKCS #1 version 1.5
   signature algorithm with SHA-512 is:

      sha512WithRSAEncryption  OBJECT IDENTIFIER  ::=  { pkcs-1 13 }

   When any of these three object identifiers appears within an
   AlgorithmIdentifier, the parameters MUST be NULL.  Implementations
   MUST accept the parameters being absent as well as present.

   The RSA signature generation process and the encoding of the result
   is described in detail in RFC 2313 [P1v1.5].


6  ASN.1 Module

PKIX1-PSS-OAEP-Algorithms
     { iso(1) identified-organization(3) dod(6)
       internet(1) security(5) mechanisms(5) pkix(7) id-mod(0)
       id-mod-pkix1-rsa-pkalgs(33) }

   DEFINITIONS EXPLICIT TAGS ::= BEGIN

   -- EXPORTS All;

   IMPORTS
Schaad, Kaliski & Housley                            Page 13


     AlgorithmIdentifier
         FROM PKIX1Explicit88 -- Found in [PROFILE]
         { iso(1) identified-organization(3) dod(6) internet(1)
           security(5) mechanisms(5) pkix(7) id-mod(0)
           id-pkix1-explicit(18) } ;


   -- ============================
   --   Basic object identifiers
   -- ============================

   pkcs-1  OBJECT IDENTIFIER  ::=  { iso(1) member-body(2)
                           us(840) rsadsi(113549) pkcs(1) 1 }

   -- When rsaEncryption is used in an AlgorithmIdentifier the
   -- parameters MUST be present and MUST be NULL.

   rsaEncryption  OBJECT IDENTIFIER  ::=  { pkcs-1 1 }

   -- When id-RSAES-OAEP is used in an AlgorithmIdentifier,
   -- and the parameters field is present, it MUST be RSAES-OAEP-params

   id-RSAES-OAEP  OBJECT IDENTIFIER  ::=  { pkcs-1 7 }

   -- When id-pSpecified is used in an AlgorithmIdentifier the
   -- parameters MUST be an OCTET STRING.

   id-pSpecified  OBJECT IDENTIFIER  ::=  { pkcs-1 9 }

   -- When id-RSASSA-PSS is used in an AlgorithmIdentifier, and the
   -- parameters field is present, it MUST be RSASSA-PSS-params.

   id-RSASSA-PSS  OBJECT IDENTIFIER  ::=  { pkcs-1 10 }

   -- When id-mgf1 is used in an AlgorithmIdentifier the parameters
   -- MUST be present and MUST be a HashAlgorithm.

   id-mgf1  OBJECT IDENTIFIER  ::=  { pkcs-1 8 }

   -- When the following OIDs are used in an AlgorithmIdentifier, the
   -- parameters MUST be present and MUST be NULL.

   sha224WithRSAEncryption  OBJECT IDENTIFIER  ::=  { pkcs-1 14 }

   sha256WithRSAEncryption  OBJECT IDENTIFIER  ::=  { pkcs-1 11 }

   sha384WithRSAEncryption  OBJECT IDENTIFIER  ::=  { pkcs-1 12 }

   sha512WithRSAEncryption  OBJECT IDENTIFIER  ::=  { pkcs-1 13 }

   -- When the following OIDs are used in an AlgorithmIdentifier the


Schaad, Kaliski & Housley                            Page 14


   -- parameters SHOULD be absent, but if the parameters are present,
   -- they MUST be NULL.

   id-sha1  OBJECT IDENTIFIER  ::=  { iso(1)
                        identified-organization(3) oiw(14)
                        secsig(3) algorithms(2) 26 }

   id-sha224  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
                        country(16) us(840) organization(1) gov(101)
                        csor(3) nistalgorithm(4) hashalgs(2) 4 }

   id-sha256  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
                        country(16) us(840) organization(1) gov(101)
                        csor(3) nistalgorithm(4) hashalgs(2) 1 }

   id-sha384  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
                        country(16) us(840) organization(1) gov(101)
                        csor(3) nistalgorithm(4) hashalgs(2) 2 }

   id-sha512  OBJECT IDENTIFIER  ::=  { joint-iso-itu-t(2)
                        country(16) us(840) organization(1) gov(101)
                        csor(3) nistalgorithm(4) hashalgs(2) 3 }

   -- =============
   --   Constants
   -- =============

   nullOctetString  OCTET STRING (SIZE (0))  ::=  ''H

   nullParameters NULL  ::=  NULL

   -- =========================
   --   Algorithm Identifiers
   -- =========================

   sha1Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-sha1,
                           parameters nullParameters  }

   sha224Identifier    AlgorithmIdentifier  ::=  {
                           algorithm id-sha224,
                           parameters nullParameters  }

   sha256Identifier    AlgorithmIdentifier  ::=  {
                           algorithm id-sha256,
                           parameters nullParameters  }

   sha384Identifier    AlgorithmIdentifier  ::=  {
                           algorithm id-sha384,
                           parameters nullParameters  }



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   sha512Identifier    AlgorithmIdentifier  ::=  {
                           algorithm id-sha512,
                           parameters nullParameters  }

   mgf1SHA1Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-mgf1,
                           parameters sha1Identifier }

   mgf1SHA224Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-mgf1,
                           parameters sha224Identifier }

   mgf1SHA256Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-mgf1,
                           parameters sha256Identifier }

   mgf1SHA384Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-mgf1,
                           parameters sha384Identifier }

   mgf1SHA512Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-mgf1,
                           parameters sha512Identifier }

   pSpecifiedEmptyIdentifier  AlgorithmIdentifier  ::=  {
                           algorithm id-pSpecified,
                           parameters nullOctetString }

   rSASSA-PSS-Default-Params RSASSA-PSS-params ::=  {
                           hashAlgorithm sha1Identifier,
                           maskGenAlgorithm mgf1SHA1Identifier,
                           saltLength 20,
                           trailerField 1  }

   rSASSA-PSS-Default-Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-RSASSA-PSS,
                           parameters rSASSA-PSS-Default-Params }

   rSASSA-PSS-SHA224-Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-RSASSA-PSS,
                           parameters rSASSA-PSS-SHA224-Params }

   rSASSA-PSS-SHA224-Params RSASSA-PSS-params ::= {
                           hashAlgorithm sha224Identifier,
                           maskGenAlgorithm mgf1SHA224Identifier,
                           saltLength 20,
                           trailerField 1  }

   rSASSA-PSS-SHA256-Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-RSASSA-PSS,
                           parameters rSASSA-PSS-SHA256-Params }


Schaad, Kaliski & Housley                            Page 16



   rSASSA-PSS-SHA256-Params RSASSA-PSS-params ::=  {
                           hashAlgorithm sha256Identifier,
                           maskGenAlgorithm mgf1SHA256Identifier,
                           saltLength 20,
                           trailerField 1  }

   rSASSA-PSS-SHA384-Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-RSASSA-PSS,
                           parameters rSASSA-PSS-SHA384-Params }

   rSASSA-PSS-SHA384-Params RSASSA-PSS-params ::= {
                           hashAlgorithm sha384Identifier,
                           maskGenAlgorithm mgf1SHA384Identifier,
                           saltLength 20,
                           trailerField 1  }

   rSASSA-PSS-SHA512-Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-RSASSA-PSS,
                           parameters rSSASSA-PSS-SHA512-params }

   rSSASSA-PSS-SHA512-params RSASSA-PSS-params ::= {
                           hashAlgorithm sha512Identifier,
                           maskGenAlgorithm mgf1SHA512Identifier,
                           saltLength 20,
                           trailerField 1  }

   rSAES-OAEP-Default-Params RSAES-OAEP-params ::=  {
                           hashFunc sha1Identifier,
                           maskGenFunc mgf1SHA1Identifier,
                           pSourceFunc pSpecifiedEmptyIdentifier  }

   rSAES-OAEP-Default-Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-RSAES-OAEP,
                           parameters rSAES-OAEP-Default-Params }

   rSAES-OAEP-SHA224-Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-RSAES-OAEP,
                           parameters rSAES-OAEP-SHA224-Params }

   rSAES-OAEP-SHA224-Params RSAES-OAEP-params ::=   {
                           hashFunc sha224Identifier,
                           maskGenFunc mgf1SHA224Identifier,
                           pSourceFunc pSpecifiedEmptyIdentifier  }

   rSAES-OAEP-SHA256-Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-RSAES-OAEP,
                           parameters rSAES-OAEP-SHA256-Params }

   rSAES-OAEP-SHA256-Params RSAES-OAEP-params ::=  {
                           hashFunc sha256Identifier,


Schaad, Kaliski & Housley                            Page 17


                           maskGenFunc mgf1SHA256Identifier,
                           pSourceFunc pSpecifiedEmptyIdentifier  }

   rSAES-OAEP-SHA384-Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-RSAES-OAEP,
                           parameters rSAES-OAEP-SHA384-Params }

   rSAES-OAEP-SHA384-Params RSAES-OAEP-params ::=  {
                           hashFunc sha384Identifier,
                           maskGenFunc mgf1SHA384Identifier,
                           pSourceFunc pSpecifiedEmptyIdentifier  }

   rSAES-OAEP-SHA512-Identifier  AlgorithmIdentifier  ::=  {
                           algorithm id-RSAES-OAEP,
                           parameters rSAES-OAEP-SHA512-Params }

   rSAES-OAEP-SHA512-Params RSAES-OAEP-params ::=  {
                           hashFunc sha512Identifier,
                           maskGenFunc mgf1SHA512Identifier,
                           pSourceFunc pSpecifiedEmptyIdentifier  }

   -- ===================
   --   Main structures
   -- ===================

   -- Used in SubjectPublicKeyInfo of X.509 Certificate.

   RSAPublicKey  ::=  SEQUENCE  {
      modulus           INTEGER,    -- n
      publicExponent    INTEGER  }  -- e


   -- AlgorithmIdentifier parameters for id-RSASSA-PSS.
   -- Note that the tags in this Sequence are explicit.

   RSASSA-PSS-params  ::=  SEQUENCE  {
      hashAlgorithm     [0] HashAlgorithm DEFAULT
                               sha1Identifier,
      maskGenAlgorithm  [1] MaskGenAlgorithm DEFAULT
                               mgf1SHA1Identifier,
      saltLength        [2] INTEGER DEFAULT 20,
      trailerField      [3] INTEGER DEFAULT 1  }

   HashAlgorithm  ::=  AlgorithmIdentifier

   MaskGenAlgorithm  ::=  AlgorithmIdentifier

   -- AlgorithmIdentifier parameters for id-RSAES-OAEP.
   -- Note that the tags in this Sequence are explicit.

   RSAES-OAEP-params  ::=  SEQUENCE  {


Schaad, Kaliski & Housley                            Page 18


      hashFunc          [0] AlgorithmIdentifier DEFAULT
                               sha1Identifier,
      maskGenFunc       [1] AlgorithmIdentifier DEFAULT
                               mgf1SHA1Identifier,
      pSourceFunc       [2] AlgorithmIdentifier DEFAULT
                               pSpecifiedEmptyIdentifier  }

   END


7  References

   This section provides normative and informative references.


7.1  Normative References

   [P1v1.5]   Kaliski, B., "PKCS #1: RSA Encryption Version 1.5",
              RFC 2313, March 1998.

   [P1v2.1]   Jonsson, J., and B. Kaliski, "PKCS #1: RSA
              Cryptography Specifications Version 2.1", RFC 3447,
              February 2003.

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

   [SHA2]     National Institute of Standards and Technology (NIST),
              FIPS 180-2: Secure Hash Standard, 1 August 2002.

   [SHA224]   Housley, R, "A 224-bit One-way Hash Function: SHA-224",
              draft-ietf-pkix-sha224-00.txt, December 2003.

   [STDWORDS] S. Bradner, "Key Words for Use in RFCs to Indicate
              Requirement Levels", RFC 2119, March 1997.

   [X.208-88] CCITT Recommendation X.208: Specification of Abstract
              Syntax Notation One (ASN.1), 1988.

   [X.209-88] CCITT Recommendation X.209: Specification of Basic
              Encoding Rules for Abstract Syntax Notation One (ASN.1),
              1988.

   [X.509-88] CCITT Recommendation X.509: The Directory -
              Authentication Framework.  1988.


7.2  Informative References

   [CMS]      Housley, R, "Cryptographic Message Syntax", RFC 3369,
              August 2002.



Schaad, Kaliski & Housley                            Page 19


   [GUIDE]    National Institute of Standards and Technology,
              Second Draft: "Key Management Guideline, Part 1:
              General Guidance."  June 2002.
              [http://csrc.nist.gov/encryption/kms/guideline-1.pdf]

   [P1363a]   IEEE P1363 working group, IEEE P1363a D11: Standard
              Specifications for Public Key Cryptography: Additional
              Techniques, December 16, 2002
              Available from http://grouper.ieee.org/groups/1363/.

   [PKALGS]   Polk, W., Housley, R., and L. Bassham, "Algorithms and
              Identifiers for the Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation
              Lists (CRL) Profile", RFC 3279, April 2002.

   [RANDOM]   Eastlake, D., Crocker, S. and J. Schiller, "Randomness
              Recommendations for Security, RFC 1750, December 1994.


8  Security Considerations

   This specification supplements RFC 3280 [PROFILE].  The security
   considerations section of that document applies to this
   specification as well.

   Implementations must protect the RSA private key.  Compromise of the
   RSA private key may result in the disclosure of all messages
   protected with that key.

   The generation of RSA public/private key pairs relies on a random
   numbers.  The use of inadequate pseudo-random number generators
   (PRNGs) to generate cryptographic keys can result in little or no
   security.  An attacker may find it much easier to reproduce the PRNG
   environment that produced the keys, searching the resulting small
   set of possibilities, rather than brute force searching the whole
   key space.  The generation of quality random numbers is difficult.
   RFC 1750 [RANDOM] offers important guidance in this area.

   Generally, good cryptographic practice employs a given RSA key pair
   in only one scheme.  This practice avoids the risk that
   vulnerability in one scheme may compromise the security of the
   other, and may be essential to maintain provable security.  While
   PKCS #1 Version 1.5 [P1v1.5] has been employed for both key
   transport and digital signature without any known bad interactions,
   such a combined use of an RSA key pair is not recommended in the
   future.  Therefore, an RSA key pair used for RSASSA-PSS signature
   generation should not also be used for other purposes.  For similar
   reasons, one RSA key pair should always be used with the same
   RSASSA-PSS parameters.  Likewise, an RSA key pair used for RSAES-
   OAEP key transport should not also be used for other purposes.  For
   similar reasons, one RSA key pair should always be used with the
   same RSAES-OAEP parameters.
Schaad, Kaliski & Housley                            Page 20



   This specification requires implementations to support the SHA-1
   one-way hash function for interoperability, but support for other
   one-way hash function is permitted.  At the time of this writing,
   the best (known) collision attacks against SHA-1 are generic attacks
   with complexity 2^80, where 80 is one-half the bit length of the
   hash value.  In general, when a one-way hash function is used with a
   digital signature scheme, a collision attack is easily translated
   into a signature forgery.  Therefore, the use of SHA-1 in a digital
   signature scheme provides a security level of no more than 80 bits.
   If a greater level of security is desired, then a secure one-way
   hash function with a longer hash value is needed.  SHA-256, SHA-384,
   and SHA-512 are reasonable choices [SHA2].

   The metrics for choosing a one-way hash function for use in digital
   signatures do not directly apply to the RSAES-OAEP key transport
   algorithm, since a collision attack on the one-way hash function
   does not directly translate into an attack on the key transport
   algorithm, unless the encoding parameters P varies (in which case a
   collision the hash value for different encoding parameters might be
   exploited).

   Nevertheless, for consistency with the practice for digital
   signature schemes, and in case the encoding parameters P is not the
   empty string, it is recommended that the same rule of thumb be
   applied to selection of a one-way hash function for use with RSAES-
   OAEP.  That is, the one-way hash function should be selected so that
   the bit length of the hash value is at least twice as long as the
   desired security level in bits.

   The key size selected impacts the strength achieved when
   implementing cryptographic services.  Thus, selection of appropriate
   key sizes is critical to implementing appropriate security.  A 1024-
   bit RSA public key and SHA-1 both provide a security level of about
   80 bits.  In [GUIDE], the National Institute of Standards and
   Technology (NIST) suggest that a security level of 80 bits is
   adequate for the protection of sensitive information until 2015.
   This recommendation is likely to be revised based on recent
   advances, and the revised recommendation is expected to be more
   conservative, suggesting that a security level of 80 bits is
   adequate for the protection of sensitive information until 2010.  If
   a security level greater than 80 bits is needed, then a longer RSA
   public key and a secure one-way hash function with a longer hash
   value are needed.  SHA-224, SHA-256, SHA-384, and SHA-512 are
   reasonable choices for such a one-way hash function and, for this
   reason, the algorithm identifiers for these one-way hash functions
   are included in the ASN.1 module in section 6.

   Current implementations MUST support 1024-bit RSA public key sizes.
   Before the end of 2007, implementations SHOULD support RSA public
   key sizes of at least 2048 bits and SHOULD support SHA-256.  This


Schaad, Kaliski & Housley                            Page 21


   requirement is intended to allow adequate time for users to deploy
   the stronger digital signature capability by 2010.

   When using RSASSA-PSS, the same one-way hash function should be
   employed for the hashAlgorithm and the maskGenAlgorithm, but it is
   not required.  Using the same one-way hash function helps with
   security analysis, and it reduces implementation complexity.
   When using RSAES-OAEP, the same one-way hash function should be
   employed for the hashFunc and the maskGenFunc, but it is not
   required. In each case, using the same one-way hash function helps
   with security analysis, and it reduces implementation complexity.

9  IANA Considerations

   Within the certificates and CRLs, algorithms are identified by
   object identifiers.  All of the object identifiers used in this
   document were assigned in Public-Key Cryptography Standards (PKCS)
   documents or by the National Institute of Standards and Technology
   (NIST).  No further action by the IANA is necessary for this
   document or any anticipated updates.


10  Author Addresses

   Russell Housley
   Vigil Security, LLC
   918 Spring Knoll Drive
   Herndon, VA 20170
   USA
   housley@vigilsec.com

   Burt Kaliski
   RSA Laboratories
   174 Middlesex Turnpike
   Bedford, MA 01730
   USA
   bkaliski@rsasecurity.com

   Jim Schaad
   Soaring Hawk Consulting
   PO Box 675
   Gold Bar, WA 98251
   USA
   jimsch@exmsft.com


11  Full Copyright Statement

   Copyright (C) The Internet Society (2004). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
Schaad, Kaliski & Housley                            Page 22


   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph
   are included on all such copies and derivative works.
   In addition, the ASN.1 modules presented in Section 5 may be used in
   whole or in part without inclusion of the copyright notice. However,
   this document itself may not be modified in any way, such as by
   removing the copyright notice or references to the Internet Society
   or other Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process shall be
   followed, or as required to translate it into languages other than
   English.
   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assigns. This
   document and the information contained herein is provided on an "AS
   IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK
   FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING BUT
   NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION HEREIN
   WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

































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