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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: Standards Track                              S. Leonard
Expires: November 1, 2014                                  Penango, Inc.
                                                          April 30, 2014


               Text Encodings of PKIX and CMS Structures
                    draft-josefsson-pkix-textual-03

Abstract

   This document describes and discuss the text encodings of Public-Key
   Infrastructure using X.509 (PKIX) Certificates, PKIX Certificate
   Revocation Lists (CRLs), PKCS #10 Certification Request Syntax, PKCS
   #7 structures, Cryptographic Message Syntax (CMS), PKCS #8 Private-
   Key Information Syntax, and Attribute Certificates.  The text
   encodings are well-known, are implemented by several applications and
   libraries, and are 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 November 1, 2014.

Copyright Notice

   Copyright (c) 2014 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



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   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
   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 . . . . . . . . . . . . . . . . . . . .  4
   3.  ABNF . . . . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   4.  Text Encoding of PKIX Certificates . . . . . . . . . . . . . .  6
     4.1.  Encoding . . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.2.  Explanatory Text . . . . . . . . . . . . . . . . . . . . .  7
     4.3.  File Extension . . . . . . . . . . . . . . . . . . . . . .  7
   5.  Text Encoding of PKIX CRLs . . . . . . . . . . . . . . . . . .  7
   6.  Text Encoding of PKCS #10 Certification Request Syntax . . . .  8
   7.  Text Encoding of PKCS #7 Cryptographic Message Syntax  . . . .  9
   8.  Text Encoding of Cryptographic Message Syntax  . . . . . . . .  9
   9.  Text Encoding of PKCS #8 Private Key Info, and One
       Asymmetric Key . . . . . . . . . . . . . . . . . . . . . . . . 10
   10. Text Encoding of PKCS #8 Encrypted Private Key Info  . . . . . 10
   11. Text Encoding of Attribute Certificates  . . . . . . . . . . . 10
   12. Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   13. IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11
   14. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 11
   15. References . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     15.1. Normative References . . . . . . . . . . . . . . . . . . . 12
     15.2. Informative References . . . . . . . . . . . . . . . . . . 12
   Appendix A.  Non-Conforming Examples . . . . . . . . . . . . . . . 13
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14


















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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:

   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.  Cryptographic Message Syntax [RFC5652].
   5.  PKCS #8: Private-Key Information Syntax [RFC5208] and One
       Asymmetric Key (in Asymmetric Key Package [RFC5958]).
   6.  An Internet Attribute Certificate Profile for Authorization
       [RFC5755].

   A disadvantage of a binary data format is 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
   using common text editors; for example, a user may concatenate
   several certificates to form a certificate chain with copy-and-paste
   operations.

   The tradition within the RFC series can be traced back to PEM
   [RFC1421], based on a proposal by M. Rose in Message Encapsulation
   [RFC0934].  Originally called "PEM encapsulation mechanism",
   "encapsulated PEM message", or (arguably) "PEM printable encoding",
   today the format is sometimes referred to as "PEM encoding".
   Variations include OpenPGP ASCII Armor [RFC2015] and OpenSSH Key File
   Format [RFC4716].

   For reasons that basically boil down to non-coordination or
   inattention, many PKIX and CMS libraries implement a text encoding
   that is similar to--but not identical with--PEM encoding.  This
   document specifies the "PKIX text encoding" format, articulates the
   de-facto rules that most implementations operate by, and provides
   recommendations that will promote interoperability going forward.
   This document also provides common nomenclature for syntax elements,
   reflecting the evolution of this de-facto standard format.  Peter
   Gutmann's X.509 Style Guide [X509SG] contains a section "base64
   Encoding" that describes 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



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   2119 [RFC2119].


2.  General Considerations

   PKIX text encoding begins with a line starting with "-----BEGIN" and
   ends with a line starting with "-----END".  Between these lines, or
   "encapsulation boundaries", are base64-encoded [RFC4648] data.  Data
   before the "-----BEGIN" and after the "-----END" encapsulation
   boundaries are permitted and MUST NOT cause parsers to malfunction.
   Furthermore, parsers MUST ignore whitespace and other non-base64
   characters and MUST handle different newline conventions.

   The type of data encoded is labeled depending on the type label in
   the "-----BEGIN" line (pre-encapsulation boundary).  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 (post-encapsulation
   boundary) as the corresponding "-----BEGIN" line.  Parsers MAY
   disregard the label on the "-----END" line instead of signaling an
   error if there is a label mismatch.

   The label type implies that the encoded data follows the specified
   syntax.  Parsers MUST handle non-conforming data gracefully.
   However, not all parsers or generators prior to this Internet-Draft
   behave consistently.  A conforming parser MAY interpret the contents
   as another label type, but ought to be aware of the security
   implications discussed in the Security Considerations section.

   Unlike legacy PEM encoding [RFC1421], OpenPGP ASCII armor, and the
   OpenSSH key file format, PKIX text encoding does NOT define or permit
   attributes to be encoded alongside the PKIX or CMS data.  Whitespace
   MAY appear between the pre-encapsulation boundary and the base64, but
   generators SHOULD NOT emit such whitespace.

   Files MAY contain multiple PKIX text encoding instances.  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 the remainder of the data (within the 64 character line
   boundary).  Parsers MAY handle other line sizes.  These requirements
   are consistent with PEM [RFC1421].






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3.  ABNF

   The ABNF of the PKIX text encoding is:

  pkixmsg    ::= preeb
                 *eolWSP
                 base64text
                 posteb

  preeb      ::= "-----BEGIN " label "-----" eol

  posteb     ::= "-----END " label "-----" eol

  base64char ::= ALPHA / DIGIT / "+" / "/"

  base64pad  ::= "="

  base64line ::= 1*base64char eol

  base64finl ::= *base64char (base64pad eol base64pad /
                 *2base64pad) eol
                 ; ...AB= <CRLF> = <CRLF> is not good, but is valid

  base64text ::= *base64line base64finl
          ; we could also use <encbinbody> from RFC 1421, which requires
          ; 16 groups of 4 chars, which means exactly 64 chars per
          ; line, except the final line, but this is more accurate

  labelchar  ::= %x21-2C / %x2E-%7E   ; any printable character,
                                      ; except hyphen

  label      ::= labelchar *(labelchar / labelchar "-" / SP) labelchar

  eol        ::= CRLF / CR / LF

  eolWSP     ::= WSP / CR / LF    ; compare with LWSP

                              Figure 1: ABNF













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   pkixmsgstrict    ::= preeb
                        strictbase64text
                        posteb

   strictbase64finl ::= *15(4base64char) (4base64char / 3base64char
                        base64pad / 2base64char 2base64pad) eol

   base64fullline   ::= 64base64char eol

   strictbase64text ::= *base64fullline strictbase64finl

                          Figure 2: ABNF (Strict)

   This specification RECOMMENDS that new implementations emit the
   strict format (Figure 2) specified above.


4.  Text Encoding of PKIX Certificates

4.1.  Encoding

   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 3: 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
   RECOMMENDED to treat "X509 CERTIFICATE" or "X.509 CERTIFICATE" as
   equivalent to "CERTIFICATE", but a valid exception may be for



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   backwards compatibility (potentially together with a warning).

4.2.  Explanatory Text

   Many tools are known to emit explanatory text before the BEGIN and
   after the END lines for PKIX certificates, more than any other type.
   If emitted, such text SHOULD be related to the certificate, such as
   providing a textual representation of key data elements in the
   certificate.

   Subject: CN=Atlantis
   Issuer: CN=Atlantis
   Validity: from 7/9/2012 3:10:38 AM UTC to 7/9/2013 3:10:37 AM UTC
   -----BEGIN CERTIFICATE-----
   MIIBmTCCAUegAwIBAgIBKjAJBgUrDgMCHQUAMBMxETAPBgNVBAMTCEF0bGFudGlz
   MB4XDTEyMDcwOTAzMTAzOFoXDTEzMDcwOTAzMTAzN1owEzERMA8GA1UEAxMIQXRs
   YW50aXMwXDANBgkqhkiG9w0BAQEFAANLADBIAkEAu+BXo+miabDIHHx+yquqzqNh
   Ryn/XtkJIIHVcYtHvIX+S1x5ErgMoHehycpoxbErZmVR4GCq1S2diNmRFZCRtQID
   AQABo4GJMIGGMAwGA1UdEwEB/wQCMAAwIAYDVR0EAQH/BBYwFDAOMAwGCisGAQQB
   gjcCARUDAgeAMB0GA1UdJQQWMBQGCCsGAQUFBwMCBggrBgEFBQcDAzA1BgNVHQEE
   LjAsgBA0jOnSSuIHYmnVryHAdywMoRUwEzERMA8GA1UEAxMIQXRsYW50aXOCASow
   CQYFKw4DAh0FAANBAKi6HRBaNEL5R0n56nvfclQNaXiDT174uf+lojzA4lhVInc0
   ILwpnZ1izL4MlI9eCSHhVQBHEp2uQdXJB+d5Byg=
   -----END CERTIFICATE-----

            Figure 4: Certificate Example with Explanatory Text

4.3.  File Extension

   Although text encodings of PKIX structures can occur anywhere, many
   tools are known to offer an option to encode PKIX structures in this
   text encoding.  To promote interoperability and to separate DER
   encodings from text encodings, This Internet-Draft RECOMMENDS that
   the extension ".crt" be used for this text encoding.  Implementations
   should be aware that in spite of this recommendation, many tools
   still default to encode certificates in this text encoding with the
   extension ".cer".


5.  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].







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   -----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 5: CRL Example

   Historically the label "CRL" has rarely been used.  Today it is not
   common and many popular tools do not understand the label.
   Therefore, this document standardizes "X509 CRL" in order to promote
   interoperability and backwards-compatibility.  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".


6.  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].

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

                        Figure 6: 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".



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7.  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 7: 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".

   PKCS #7 is an old standard that has long been superseded by CMS.
   Implementations SHOULD NOT generate PKCS #7 when CMS is an
   alternative.


8.  Text Encoding of Cryptographic Message Syntax

   Cryptographic Message Syntax structures are encoded using the "CMS"
   label.  The encoded data MUST be a DER encoded ASN.1 "ContentInfo"
   structure as described in [RFC5652].

   -----BEGIN CMS-----
   MIGDBgsqhkiG9w0BCRABCaB0MHICAQAwDQYLKoZIhvcNAQkQAwgwXgYJKoZIhvcN
   AQcBoFEET3icc87PK0nNK9ENqSxItVIoSa0o0S/ISczMs1ZIzkgsKk4tsQ0N1nUM
   dvb05OXi5XLPLEtViMwvLVLwSE0sKlFIVHAqSk3MBkkBAJv0Fx0=
   -----END CMS-----

                           Figure 8: CMS Example

   CMS is the IETF successor to PKCS #7.  Section 1.1.1 of [RFC5652]
   describes the changes since PKCS #7 v1.5.  Implementations SHOULD
   generate CMS when it is an alternative, promoting ineroperability and
   forwards-compatibility.





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9.  Text Encoding of PKCS #8 Private Key Info, and One Asymmetric Key

   The PrivateKeyInfo structure of PKCS #8 Private Key Information
   Syntax, renamed to OneAsymmetricKey in [RFC5958], is encoded using
   the "PRIVATE KEY" label.  The encoded data MUST be a DER encoded
   ASN.1 "PrivateKeyInfo" structure as described in PKCS #8, or the
   "OneAsymmetricKey" structure as described in [RFC5958].  The two are
   semantically identical, and can be distinguished by version number.


   -----BEGIN PRIVATE KEY-----
   MIGEAgEAMBAGByqGSM49AgEGBSuBBAAKBG0wawIBAQQgVcB/UNPxalR9zDYAjQIf
   jojUDiQuGnSJrFEEzZPT/92hRANCAASc7UJtgnF/abqWM60T3XNJEzBv5ez9TdwK
   H0M6xpM2q+53wmsN/eYLdgtjgBd3DBmHtPilCkiFICXyaA8z9LkJ
   -----END PRIVATE KEY-----

                 Figure 9: PKCS #8 PrivateKeyInfo Example


10.  Text Encoding of PKCS #8 Encrypted Private Key Info

   The EncryptedPrivateKeyInfo structure of PKCS #8 Private Key
   Information Syntax, called the same in [RFC5958], is encoded using
   the "ENCRYPTED PRIVATE KEY" label.  The encoded data MUST be a DER
   encoded ASN.1 "EncryptedPrivateKeyInfo" structure as described in
   PKCS #8 and [RFC5958].

   -----BEGIN ENCRYPTED PRIVATE KEY-----
   MIHNMEAGCSqGSIb3DQEFDTAzMBsGCSqGSIb3DQEFDDAOBAghhICA6T/51QICCAAw
   FAYIKoZIhvcNAwcECBCxDgvI59i9BIGIY3CAqlMNBgaSI5QiiWVNJ3IpfLnEiEsW
   Z0JIoHyRmKK/+cr9QPLnzxImm0TR9s4JrG3CilzTWvb0jIvbG3hu0zyFPraoMkap
   8eRzWsIvC5SVel+CSjoS2mVS87cyjlD+txrmrXOVYDE+eTgMLbrLmsWh3QkCTRtF
   QC7k0NNzUHTV9yGDwfqMbw==
   -----END ENCRYPTED PRIVATE KEY-----

            Figure 10: PKCS #8 EncryptedPrivateKeyInfo Example


11.  Text Encoding of Attribute Certificates

   Attribute certificates are encoded using the "ATTRIBUTE CERTIFICATE"
   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 11: Attribute Certificate Example


12.  Security Considerations

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

   Ambiguities are introduced by having more than one canonical encoding
   of the same data.  The first ambiguity 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.  Variations of whitespace and non-base64 alphabetic
   characters can create further ambiguities.  Implementations that rely
   on canonical representation or the ability to fingerprint a
   particular data format need to understand that this Internet-Draft
   does not define canonical encodings.  If canonical encodings are
   desired, the encoded structure must be decoded and processed into a
   canonical form (namely, DER encoding).  Data encoding ambiguities
   also create opportunities for side channels.


13.  IANA Considerations

   This document implies no IANA Considerations.


14.  Acknowledgements

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



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15.  References

15.1.  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.

   [RFC5208]  Kaliski, B., "Public-Key Cryptography Standards (PKCS) #8:
              Private-Key Information Syntax Specification Version 1.2",
              RFC 5208, May 2008.

   [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.

   [RFC5652]  Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, September 2009.

   [RFC5755]  Farrell, S., Housley, R., and S. Turner, "An Internet
              Attribute Certificate Profile for Authorization",
              RFC 5755, January 2010.

   [RFC5958]  Turner, S., "Asymmetric Key Packages", RFC 5958,
              August 2010.

   [CCITT.X690.2002]
              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.

15.2.  Informative References

   [RFC0934]  Rose, M. and E. Stefferud, "Proposed standard for message
              encapsulation", RFC 934, January 1985.




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   [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.

   [RFC4716]  Galbraith, J. and R. Thayer, "The Secure Shell (SSH)
              Public Key File Format", RFC 4716, November 2006.

   [X509SG]   Gutmann, P., "X.509 Style Guide", WWW http://
              www.cs.auckland.ac.nz/~pgut001/pubs/x509guide.txt,
              October 2000.


Appendix A.  Non-Conforming 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 12: 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 13: 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 14: Non-standard 'NEW' PKCS #10 Example


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

            Figure 15: Non-standard 'CERTIFICATE CHAIN' Example










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Authors' Addresses

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

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


   Sean Leonard
   Penango, Inc.
   11400 West Olympic Boulevard
   Suite 1500
   Los Angeles, CA  90064
   USA

   Email: dev+ietf@seantek.com
   URI:   http://www.penango.com/






























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