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Versions: 00 01 02 03 04 05 06 07 08 09 10 RFC 7468

Network Working Group                                       S. Josefsson
Internet-Draft                                                    SJD AB
Intended status: Informational                          January 27, 2012
Expires: July 30, 2012


           Text Encodings of Some Security Related Structures
                    draft-josefsson-pkix-textual-00

Abstract

   This document describe and discuss the text encodings of Public-Key
   Infrastructure using X.509 (PKIX) Certificates, PKIX Certificate
   Revocation Lists (CRLs), PKCS #10 Certificate Request Syntax, PKCS #7
   structures, and Attribute Certificates.  The text encodings are well-
   known, implemented by several applications and libraries, and is
   widely deployed.  This document is intended to articulate the de-
   facto rules that existing implementations operate by, and to give
   recommendations that will promote interoperability going forward.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   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."

   This Internet-Draft will expire on July 30, 2012.

Copyright Notice

   Copyright (c) 2012 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must



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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  General Considerations . . . . . . . . . . . . . . . . . . . .  3
   3.  Text Encoding of PKIX Certificate  . . . . . . . . . . . . . .  4
   4.  Text Encoding of PKIX CRLs . . . . . . . . . . . . . . . . . .  5
   5.  Text Encoding of PKCS #10 Certification Request Syntax . . . .  5
   6.  Text Encoding of PKCS #7 Cryptographic Message Syntax  . . . .  6
   7.  Text Encoding of Attribute Certificates  . . . . . . . . . . .  6
   8.  Non-comforming Examples  . . . . . . . . . . . . . . . . . . .  7
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . .  8
   10. IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  9
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  9
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     12.1.  Normative References  . . . . . . . . . . . . . . . . . .  9
     12.2.  Informative References  . . . . . . . . . . . . . . . . . 10
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10





























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1.  Introduction

   Several security-related standards used on the Internet define data
   formats that are normally encoded using Distinguished Encoding Rules
   (DER) [CCITT.X690.2002], which is a binary data format.  This
   document is about text encodings of some of these formats.  In
   particular, we describe text encodings for the following formats.

   1.  Internet X.509 Public Key Infrastructure Certificate and
       Certificate Revocation List (CRL) Profile [RFC5280], for both
       Certificates and Certificate Revocation Lists (CRLs).
   2.  PKCS #10: Certification Request Syntax [RFC2986].
   3.  PKCS #7: Cryptographic Message Syntax [RFC2315].
   4.  An Internet Attribute Certificate Profile for Authorization
       [RFC5755].

   One motivation for a text encoding is that a binary data format has
   the disadvantage that it cannot be interchanged in textual
   transports, such as e-mail or text documents.  One advantage with
   text encodings is that they are easy to modify without special-
   purpose tools; for example, using a text editor you may concatenate
   several certificates to form a certificate chain.

   The exact history of the text encodings are unknown to the author of
   this document, however the tradition within the RFC series can be
   traced back to PEM [RFC1421] and OpenPGP [RFC2015].  These text
   encodings are sometimes referred to as "PEM encodings".  Peter
   Gutmann's X.509 Style Guide [X509SG] contains a section "base64
   Encoding" that describe the formats and contains suggestions similar
   to what is in this document.

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119 [RFC2119].


2.  General Considerations

   The structure of a text encoding is such that they begin with a line
   starting with "-----BEGIN" and end with a line starting with
   "-----END".  Between these markers are Base64 [RFC4648] encoded data.
   Data before the "-----BEGIN" and after the "-----END" marker are
   permitted and MUST NOT cause parsers to malfunction.  Further,
   parsers MUST ignore whitespace and other non-alphabetic characters
   and MUST handle different newline conventions.

   The type of data encoded is labeled depending on the type label in



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   the "-----BEGIN" line.  For example, the line may be "-----BEGIN
   CERTIFICATE-----" to indicate that the content is a PKIX Certificate
   (see further below).  Generators MUST put the same label on the
   "-----END" line as the corresponding "-----BEGIN" line.  Parses MAY
   disregard the label on the "-----END" lines instead of signalling an
   error if there is a label mismatch.

   The label type is not a guarantee that the encoded data follows the
   implied syntax.  Parsers MUST handle non-conforming data gracefully.

   Files MAY contain multiple instances of the text encoded
   representation.  This is used, for example, when a file contains
   several certificates.  Whether the instances are ordered or unordered
   depends on the context.

   Generators MUST wrap the base64 encoded lines so that each line
   consists of exactly 64 characters except for the final line which
   will encode as much data is left (within the 64 character line
   boundary).  Parser MAY handle other line sizes.


3.  Text Encoding of PKIX Certificate

   PKIX Certificates are encoded using the "CERTIFICATE" label.  The
   encoded data MUST be a DER encoded ASN.1 "Certificate" structure as
   described in section 4 of [RFC5280].

   -----BEGIN CERTIFICATE-----
   MIICLDCCAdKgAwIBAgIBADAKBggqhkjOPQQDAjB9MQswCQYDVQQGEwJCRTEPMA0G
   A1UEChMGR251VExTMSUwIwYDVQQLExxHbnVUTFMgY2VydGlmaWNhdGUgYXV0aG9y
   aXR5MQ8wDQYDVQQIEwZMZXV2ZW4xJTAjBgNVBAMTHEdudVRMUyBjZXJ0aWZpY2F0
   ZSBhdXRob3JpdHkwHhcNMTEwNTIzMjAzODIxWhcNMTIxMjIyMDc0MTUxWjB9MQsw
   CQYDVQQGEwJCRTEPMA0GA1UEChMGR251VExTMSUwIwYDVQQLExxHbnVUTFMgY2Vy
   dGlmaWNhdGUgYXV0aG9yaXR5MQ8wDQYDVQQIEwZMZXV2ZW4xJTAjBgNVBAMTHEdu
   dVRMUyBjZXJ0aWZpY2F0ZSBhdXRob3JpdHkwWTATBgcqhkjOPQIBBggqhkjOPQMB
   BwNCAARS2I0jiuNn14Y2sSALCX3IybqiIJUvxUpj+oNfzngvj/Niyv2394BWnW4X
   uQ4RTEiywK87WRcWMGgJB5kX/t2no0MwQTAPBgNVHRMBAf8EBTADAQH/MA8GA1Ud
   DwEB/wQFAwMHBgAwHQYDVR0OBBYEFPC0gf6YEr+1KLlkQAPLzB9mTigDMAoGCCqG
   SM49BAMCA0gAMEUCIDGuwD1KPyG+hRf88MeyMQcqOFZD0TbVleF+UsAGQ4enAiEA
   l4wOuDwKQa+upc8GftXE2C//4mKANBC6It01gUaTIpo=
   -----END CERTIFICATE-----

                       Figure 1: Certificate Example

   Historically the label "X509 CERTIFICATE" and also, less common,
   "X.509 CERTIFICATE" have been used.  Generators conforming to this
   document MUST generate "CERTIFICATE" labels and MUST NOT generate
   "X509 CERTIFICATE" or "X.509 CERTIFICATE" labels.  Parsers are NOT



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   RECOMMENDED to treat "X509 CERTIFICATE" or "X.509 CERTIFICATE" as
   equivalent to "CERTIFICATE", but a valid exception may be for
   backwards compatibility (potentially together with a warning).


4.  Text Encoding of PKIX CRLs

   PKIX CRLs are encoded using the "X509 CRL" label.  The encoded data
   MUST be a DER encoded ASN.1 "CertificateList" structure as described
   in section 5 of [RFC5280].

   -----BEGIN X509 CRL-----
   MIIB9DCCAV8CAQEwCwYJKoZIhvcNAQEFMIIBCDEXMBUGA1UEChMOVmVyaVNpZ24s
   IEluYy4xHzAdBgNVBAsTFlZlcmlTaWduIFRydXN0IE5ldHdvcmsxRjBEBgNVBAsT
   PXd3dy52ZXJpc2lnbi5jb20vcmVwb3NpdG9yeS9SUEEgSW5jb3JwLiBieSBSZWYu
   LExJQUIuTFREKGMpOTgxHjAcBgNVBAsTFVBlcnNvbmEgTm90IFZhbGlkYXRlZDEm
   MCQGA1UECxMdRGlnaXRhbCBJRCBDbGFzcyAxIC0gTmV0c2NhcGUxGDAWBgNVBAMU
   D1NpbW9uIEpvc2Vmc3NvbjEiMCAGCSqGSIb3DQEJARYTc2ltb25Aam9zZWZzc29u
   Lm9yZxcNMDYxMjI3MDgwMjM0WhcNMDcwMjA3MDgwMjM1WjAjMCECEC4QNwPfRoWd
   elUNpllhhTgXDTA2MTIyNzA4MDIzNFowCwYJKoZIhvcNAQEFA4GBAD0zX+J2hkcc
   Nbrq1Dn5IKL8nXLgPGcHv1I/le1MNo9t1ohGQxB5HnFUkRPAY82fR6Epor4aHgVy
   b+5y+neKN9Kn2mPF4iiun+a4o26CjJ0pArojCL1p8T0yyi9Xxvyc/ezaZ98HiIyP
   c3DGMNR+oUmSjKZ0jIhAYmeLxaPHfQwR
   -----END X509 CRL-----

                           Figure 2: CRL Example

   Historically the label "CRL" have been used, but today it is not
   common and several popular tools do not understand the label.
   Generators conforming to this document MUST generate "X509 CRL"
   labels and MUST NOT generate "CRL" labels.  Parsers are NOT
   RECOMMENDED to treat "CRL" as equivalent to "X509 CRL".


5.  Text Encoding of PKCS #10 Certification Request Syntax

   PKCS #10 Certification Requests are encoded using the "CERTIFICATE
   REQUEST" label.  The encoded data MUST be a DER encoded ASN.1
   "CertificationRequest" structure as described in [RFC2986].












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   -----BEGIN CERTIFICATE REQUEST-----
   MIIBWDCCAQcCAQAwTjELMAkGA1UEBhMCU0UxJzAlBgNVBAoTHlNpbW9uIEpvc2Vm
   c3NvbiBEYXRha29uc3VsdCBBQjEWMBQGA1UEAxMNam9zZWZzc29uLm9yZzBOMBAG
   ByqGSM49AgEGBSuBBAAhAzoABLLPSkuXY0l66MbxVJ3Mot5FCFuqQfn6dTs+9/CM
   EOlSwVej77tj56kj9R/j9Q+LfysX8FO9I5p3oGIwYAYJKoZIhvcNAQkOMVMwUTAY
   BgNVHREEETAPgg1qb3NlZnNzb24ub3JnMAwGA1UdEwEB/wQCMAAwDwYDVR0PAQH/
   BAUDAwegADAWBgNVHSUBAf8EDDAKBggrBgEFBQcDATAKBggqhkjOPQQDAgM/ADA8
   AhxBvfhxPFfbBbsE1NoFmCUczOFApEuQVUw3ZP69AhwWXk3dgSUsKnuwL5g/ftAY
   dEQc8B8jAcnuOrfU
   -----END CERTIFICATE REQUEST-----

                        Figure 3: PKCS #10 Example

   The label "NEW CERTIFICATE REQUEST" is also in wide use.  Generators
   conforming to this document MUST generate "CERTIFICATE REQUEST"
   labels.  Parsers MAY treat "NEW CERTIFICATE REQUEST" as equivalent to
   "CERTIFICATE REQUEST".


6.  Text Encoding of PKCS #7 Cryptographic Message Syntax

   PKCS #7 Cryptographic Message Syntax structures are encoded using the
   "PKCS7" label.  The encoded data MUST be a DER encoded ASN.1
   "ContentInfo" structure as described in [RFC2315].

   -----BEGIN PKCS7-----
   MIHjBgsqhkiG9w0BCRABF6CB0zCB0AIBADFho18CAQCgGwYJKoZIhvcNAQUMMA4E
   CLfrI6dr0gUWAgITiDAjBgsqhkiG9w0BCRADCTAUBggqhkiG9w0DBwQIZpECRWtz
   u5kEGDCjerXY8odQ7EEEromZJvAurk/j81IrozBSBgkqhkiG9w0BBwEwMwYLKoZI
   hvcNAQkQAw8wJDAUBggqhkiG9w0DBwQI0tCBcU09nxEwDAYIKwYBBQUIAQIFAIAQ
   OsYGYUFdAH0RNc1p4VbKEAQUM2Xo8PMHBoYdqEcsbTodlCFAZH4=
   -----END PKCS7-----

                         Figure 4: PKCS #7 Example

   The label "CERTIFICATE CHAIN" has been in use to denote a
   degenerative PKCS #7 structure that contains only a list of
   certificates.  Several modern tools do not support this label.
   Generators MUST NOT generate the "CERTIFICATE CHAIN" label.  Parsers
   are NOT RECOMMENDED to treat "CERTIFICATE CHAIN" as equivalent to
   "PKCS7".


7.  Text Encoding of Attribute Certificates

   Attribute certificates are encoded using the "ATTRIBUTE CERTIFICATES"
   label.  The encoded data MUST be a DER encoded ASN.1
   "AttributeCertificate" structure as described in [RFC5755].



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   -----BEGIN ATTRIBUTE CERTIFICATE-----
   MIICKzCCAZQCAQEwgZeggZQwgYmkgYYwgYMxCzAJBgNVBAYTAlVTMREwDwYDVQQI
   DAhOZXcgWW9yazEUMBIGA1UEBwwLU3RvbnkgQnJvb2sxDzANBgNVBAoMBkNTRTU5
   MjE6MDgGA1UEAwwxU2NvdHQgU3RhbGxlci9lbWFpbEFkZHJlc3M9c3N0YWxsZXJA
   aWMuc3VueXNiLmVkdQIGARWrgUUSoIGMMIGJpIGGMIGDMQswCQYDVQQGEwJVUzER
   MA8GA1UECAwITmV3IFlvcmsxFDASBgNVBAcMC1N0b255IEJyb29rMQ8wDQYDVQQK
   DAZDU0U1OTIxOjA4BgNVBAMMMVNjb3R0IFN0YWxsZXIvZW1haWxBZGRyZXNzPXNz
   dGFsbGVyQGljLnN1bnlzYi5lZHUwDQYJKoZIhvcNAQEFBQACBgEVq4FFSjAiGA8z
   OTA3MDIwMTA1MDAwMFoYDzM5MTEwMTMxMDUwMDAwWjArMCkGA1UYSDEiMCCGHmh0
   dHA6Ly9pZGVyYXNobi5vcmcvaW5kZXguaHRtbDANBgkqhkiG9w0BAQUFAAOBgQAV
   M9axFPXXozEFcer06bj9MCBBCQLtAM7ZXcZjcxyva7xCBDmtZXPYUluHf5OcWPJz
   5XPus/xS9wBgtlM3fldIKNyNO8RsMp6Ocx+PGlICc7zpZiGmCYLl64lAEGPO/bsw
   Smluak1aZIttePeTAHeJJs8izNJ5aR3Wcd3A5gLztQ==
   -----END ATTRIBUTE CERTIFICATE-----

                  Figure 5: Attribute Certificate Example


8.  Non-comforming Examples

   This section contains examples for the non-recommended label variants
   described earlier in this document.  As discussed earlier, supporting
   these are not required and sometimes discouraged.  Still, they can be
   useful for interoperability testing and for easy reference.

   -----BEGIN X509 CERTIFICATE-----
   MIICLDCCAdKgAwIBAgIBADAKBggqhkjOPQQDAjB9MQswCQYDVQQGEwJCRTEPMA0G
   A1UEChMGR251VExTMSUwIwYDVQQLExxHbnVUTFMgY2VydGlmaWNhdGUgYXV0aG9y
   aXR5MQ8wDQYDVQQIEwZMZXV2ZW4xJTAjBgNVBAMTHEdudVRMUyBjZXJ0aWZpY2F0
   ZSBhdXRob3JpdHkwHhcNMTEwNTIzMjAzODIxWhcNMTIxMjIyMDc0MTUxWjB9MQsw
   CQYDVQQGEwJCRTEPMA0GA1UEChMGR251VExTMSUwIwYDVQQLExxHbnVUTFMgY2Vy
   dGlmaWNhdGUgYXV0aG9yaXR5MQ8wDQYDVQQIEwZMZXV2ZW4xJTAjBgNVBAMTHEdu
   dVRMUyBjZXJ0aWZpY2F0ZSBhdXRob3JpdHkwWTATBgcqhkjOPQIBBggqhkjOPQMB
   BwNCAARS2I0jiuNn14Y2sSALCX3IybqiIJUvxUpj+oNfzngvj/Niyv2394BWnW4X
   uQ4RTEiywK87WRcWMGgJB5kX/t2no0MwQTAPBgNVHRMBAf8EBTADAQH/MA8GA1Ud
   DwEB/wQFAwMHBgAwHQYDVR0OBBYEFPC0gf6YEr+1KLlkQAPLzB9mTigDMAoGCCqG
   SM49BAMCA0gAMEUCIDGuwD1KPyG+hRf88MeyMQcqOFZD0TbVleF+UsAGQ4enAiEA
   l4wOuDwKQa+upc8GftXE2C//4mKANBC6It01gUaTIpo=
   -----END X509 CERTIFICATE-----

             Figure 6: Non-standard 'X509' Certificate Example










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   -----BEGIN X.509 CERTIFICATE-----
   MIICLDCCAdKgAwIBAgIBADAKBggqhkjOPQQDAjB9MQswCQYDVQQGEwJCRTEPMA0G
   A1UEChMGR251VExTMSUwIwYDVQQLExxHbnVUTFMgY2VydGlmaWNhdGUgYXV0aG9y
   aXR5MQ8wDQYDVQQIEwZMZXV2ZW4xJTAjBgNVBAMTHEdudVRMUyBjZXJ0aWZpY2F0
   ZSBhdXRob3JpdHkwHhcNMTEwNTIzMjAzODIxWhcNMTIxMjIyMDc0MTUxWjB9MQsw
   CQYDVQQGEwJCRTEPMA0GA1UEChMGR251VExTMSUwIwYDVQQLExxHbnVUTFMgY2Vy
   dGlmaWNhdGUgYXV0aG9yaXR5MQ8wDQYDVQQIEwZMZXV2ZW4xJTAjBgNVBAMTHEdu
   dVRMUyBjZXJ0aWZpY2F0ZSBhdXRob3JpdHkwWTATBgcqhkjOPQIBBggqhkjOPQMB
   BwNCAARS2I0jiuNn14Y2sSALCX3IybqiIJUvxUpj+oNfzngvj/Niyv2394BWnW4X
   uQ4RTEiywK87WRcWMGgJB5kX/t2no0MwQTAPBgNVHRMBAf8EBTADAQH/MA8GA1Ud
   DwEB/wQFAwMHBgAwHQYDVR0OBBYEFPC0gf6YEr+1KLlkQAPLzB9mTigDMAoGCCqG
   SM49BAMCA0gAMEUCIDGuwD1KPyG+hRf88MeyMQcqOFZD0TbVleF+UsAGQ4enAiEA
   l4wOuDwKQa+upc8GftXE2C//4mKANBC6It01gUaTIpo=
   -----END X.509 CERTIFICATE-----

            Figure 7: Non-standard 'X.509' Certificate Example


   -----BEGIN NEW CERTIFICATE REQUEST-----
   MIIBWDCCAQcCAQAwTjELMAkGA1UEBhMCU0UxJzAlBgNVBAoTHlNpbW9uIEpvc2Vm
   c3NvbiBEYXRha29uc3VsdCBBQjEWMBQGA1UEAxMNam9zZWZzc29uLm9yZzBOMBAG
   ByqGSM49AgEGBSuBBAAhAzoABLLPSkuXY0l66MbxVJ3Mot5FCFuqQfn6dTs+9/CM
   EOlSwVej77tj56kj9R/j9Q+LfysX8FO9I5p3oGIwYAYJKoZIhvcNAQkOMVMwUTAY
   BgNVHREEETAPgg1qb3NlZnNzb24ub3JnMAwGA1UdEwEB/wQCMAAwDwYDVR0PAQH/
   BAUDAwegADAWBgNVHSUBAf8EDDAKBggrBgEFBQcDATAKBggqhkjOPQQDAgM/ADA8
   AhxBvfhxPFfbBbsE1NoFmCUczOFApEuQVUw3ZP69AhwWXk3dgSUsKnuwL5g/ftAY
   dEQc8B8jAcnuOrfU
   -----END NEW CERTIFICATE REQUEST-----

               Figure 8: Non-standard 'NEW' PKCS #10 Example


   -----BEGIN CERTIFICATE CHAIN-----
   MIHjBgsqhkiG9w0BCRABF6CB0zCB0AIBADFho18CAQCgGwYJKoZIhvcNAQUMMA4E
   CLfrI6dr0gUWAgITiDAjBgsqhkiG9w0BCRADCTAUBggqhkiG9w0DBwQIZpECRWtz
   u5kEGDCjerXY8odQ7EEEromZJvAurk/j81IrozBSBgkqhkiG9w0BBwEwMwYLKoZI
   hvcNAQkQAw8wJDAUBggqhkiG9w0DBwQI0tCBcU09nxEwDAYIKwYBBQUIAQIFAIAQ
   OsYGYUFdAH0RNc1p4VbKEAQUM2Xo8PMHBoYdqEcsbTodlCFAZH4=
   -----END CERTIFICATE CHAIN-----

            Figure 9: Non-standard 'CERTIFICATE CHAIN' Example


9.  Security Considerations

   Data in this format is often originating from untrusted sources, thus
   parsers must be prepared to handle unexpected data without causing
   security vulnerabilities.



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   By having more than one canonical encoding of the same data, an
   ambiguity is introduced.  The first one is introduced by permitting
   the text encoded representation instead of the binary DER encoding,
   but further ambiguities arise when multiple labels are treated as
   similar.  Even further, variations of whitespace and non-base64
   alphabetic characters can further create ambiguities.
   Implementations that rely on canonical representation or the ability
   to fingerprint a particular data format will need to take this into
   account.  Data encoding ambiguities also create opportunities for
   side channels.


10.  IANA Considerations

   This document implies no IANA Considerations.


11.  Acknowledgements

   Peter Gutmann suggested to document labels for Attribute Certificates
   and PKCS #7 messages, and to add examples for the non-standard
   variants.


12.  References

12.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2315]  Kaliski, B., "PKCS #7: Cryptographic Message Syntax
              Version 1.5", RFC 2315, March 1998.

   [RFC2986]  Nystrom, M. and B. Kaliski, "PKCS #10: Certification
              Request Syntax Specification Version 1.7", RFC 2986,
              November 2000.

   [RFC4648]  Josefsson, S., "The Base16, Base32, and Base64 Data
              Encodings", RFC 4648, October 2006.

   [RFC5280]  Cooper, D., Santesson, S., Farrell, S., Boeyen, S.,
              Housley, R., and W. Polk, "Internet X.509 Public Key
              Infrastructure Certificate and Certificate Revocation List
              (CRL) Profile", RFC 5280, May 2008.

   [RFC5755]  Farrell, S., Housley, R., and S. Turner, "An Internet
              Attribute Certificate Profile for Authorization",



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              RFC 5755, January 2010.

   [CCITT.X690.2002]
              International International Telephone and Telegraph
              Consultative Committee, "ASN.1 encoding rules:
              Specification of basic encoding Rules (BER), Canonical
              encoding rules (CER) and Distinguished encoding rules
              (DER)", CCITT Recommendation X.690, July 2002.

12.2.  Informative References

   [RFC1421]  Linn, J., "Privacy Enhancement for Internet Electronic
              Mail: Part I: Message Encryption and Authentication
              Procedures", RFC 1421, February 1993.

   [RFC2015]  Elkins, M., "MIME Security with Pretty Good Privacy
              (PGP)", RFC 2015, October 1996.

   [X509SG]   Gutmann, P., "X.509 Style Guide", WWW http://
              www.cs.auckland.ac.nz/~pgut001/pubs/x509guide.txt.


Author's Address

   Simon Josefsson
   SJD AB
   Johan Olof Wallins Vaeg 13
   Solna  171 64
   SE

   Email: simon@josefsson.org
   URI:   http://josefsson.org/



















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