I-D signatures update: Update to Digital Signatures on Internet-Draft Documents

Internet Engineering Task Force (IETF)                        R. Housley
Request for Comments: 8358                                Vigil Security
Updates: 5485                                                 March 2018
Category: Informational
ISSN: 2070-1721


        Update to Digital Signatures on Internet-Draft Documents

Abstract

   RFC 5485 specifies the conventions for digital signatures on
   Internet-Drafts.  The Cryptographic Message Syntax (CMS) is used to
   create a detached signature, which is stored in a separate companion
   file so that no existing utilities are impacted by the addition of
   the digital signature.

   The RFC Editor recently published the first RFC that includes non-
   ASCII characters in a text file.  The conventions specified in RFC
   7997 were followed.  We assume that non-ASCII characters will soon
   start appearing in Internet-Drafts as well.  This document updates
   the handling of digital signatures on Internet-Drafts that contain
   non-ASCII characters in a text file.

   This document updates RFC 5485.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Not all documents
   approved by the IESG are candidates for any level of Internet
   Standard; see Section 2 of RFC 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   https://www.rfc-editor.org/info/rfc8358.

Copyright Notice

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   document authors.  All rights reserved.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     1.2.  ASN.1 . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  Detached Signature Files  . . . . . . . . . . . . . . . . . .   4
   3.  Additional Content Types  . . . . . . . . . . . . . . . . . .   4
   4.  Need for Canonicalization . . . . . . . . . . . . . . . . . .   5
     4.1.  ASCII, UTF-8, and HTML File Canonicalization  . . . . . .   6
     4.2.  XML File Canonicalization . . . . . . . . . . . . . . . .   6
     4.3.  No Canonicalization of Other File Formats . . . . . . . .   7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   7
   7.  Deployment and Operational Considerations . . . . . . . . . .   7
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   RFC 5485 [IDSIG] specifies the conventions for digital signatures on
   Internet-Drafts.  The Cryptographic Message Syntax (CMS) [CMS] is
   used to create a detached signature, which is stored in a separate
   companion file so that no existing utilities are impacted by the
   addition of the digital signature.

   The RFC Editor recently published the first RFC that includes non-
   ASCII characters in a text file.  The conventions specified in RFC
   7997 [RFCED] were followed.  We assume that non-ASCII characters will
   soon start appearing in Internet-Drafts as well.  This document
   updates the handling of digital signatures on Internet-Drafts that
   contain non-ASCII characters in a text file.

   This document updates RFC 5485 [IDSIG], which contains the
   conventions that have been used by the IETF Secretariat to digitally
   sign Internet-Drafts for the past few years.  The IETF Secretariat
   generates the digital signature shortly after the Internet-Draft is
   posted in the repository.

   The digital signature allows anyone to confirm that the contents of
   the Internet-Draft have not been altered since the time that the
   document was signed.

   The digital signature is intended to provide a straightforward way
   for anyone to determine whether a particular file contains the
   Internet-Draft that was made available by the IETF Secretariat.  The
   signing-time associated with the signature provides the wall clock
   time at which the signature was generated; it is not intended to
   provide a trusted timestamp.

1.1.  Terminology

   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
   BCP 14 [STDWORDS] [STDWORDS2] when, and only when, they appear in all
   capitals, as shown here.

1.2.  ASN.1

   The CMS uses Abstract Syntax Notation One (ASN.1) [X.680].  ASN.1 is
   a formal notation used for describing data protocols, regardless of
   the programming language used by the implementation.  Encoding rules
   describe how the values defined in ASN.1 will be represented for
   transmission.  The Basic Encoding Rules (BER) [X.690] are the most
   widely employed rule set, but they offer more than one way to
   represent data structures.  For example, definite length encoding and
   indefinite length encoding are supported.  This flexibility is not
   desirable when digital signatures are used.  As a result, the
   Distinguished Encoding Rules (DER) [X.690] were invented.  DER is a
   subset of BER that ensures a single way to represent a given value.
   For example, DER always employs definite length encoding.

2.  Detached Signature Files

   All Internet-Draft file names begin with "draft-".  The next portion
   of the file name depends on the source of the document.  For example,
   documents from IETF working groups usually have "ietf-" followed by
   the working group abbreviation, and this is followed by a string that
   helps people figure out the subject of the document.

   All Internet-Draft file names end with a hyphen followed by a two
   digit version number and a suffix.  The suffix indicates the type of
   file.  For example, a text file will have a suffix of ".txt".  Today,
   plain text files are the most common, but the RFC Editor has
   announced plans to make use of other formats [RFCSERIES].  Each file
   format employs a different suffix.

   Going forward, one cannot assume that a text file with a suffix of
   ".txt" will contain only ASCII characters.

   The companion signature file has exactly the same file name as the
   RFC or Internet-Draft, except that ".p7s" is added to the end.  This
   file name suffix conforms to the conventions in RFC 5751 [MSG].  Here
   are a few example names:

      Internet-Draft: draft-ietf-example-widgets-03.txt
      Signature File: draft-ietf-example-widgets-03.txt.p7s

      Internet-Draft: draft-ietf-example-widgets-03.pdf
      Signature File: draft-ietf-example-widgets-03.pdf.p7s

      Internet-Draft: draft-housley-internet-draft-sig-file-00.txt
      Signature File: draft-housley-internet-draft-sig-file-00.txt.p7s

3.  Additional Content Types

   The CMS is used to construct the detached signatures for Internet-
   Drafts.  The CMS ContentInfo content type MUST always be present, and
   it MUST encapsulate the CMS SignedData content type.  Since a
   detached signature is being created, the CMS SignedData content type
   MUST NOT encapsulate the Internet-Draft.  The CMS detached signature
   is summarized in RFC 5485 [IDSIG].

   The SignedData.SignerInfo.EncapsulatedContentInfo.eContentType value
   MUST identify the format of the Internet-Draft that is being signed.
   Section 5 of RFC 5485 [IDSIG] lists the file formats and the
   associated content type.  This document expands that list as follows:

      File Format                        Content Type
      -----------                        ------------
      ASCII text                         id-ct-asciiTextWithCRLF
      UTF-8 text (includes non-ASCII)    id-ct-utf8TextWithCRLF
      HyperText Markup Language (HTML)   id-ct-htmlWithCRLF
      EPUB                               id-ct-epub
      Extensible Markup Language (XML)   id-ct-xml
      Portable Document Format (PDF)     id-ct-pdf
      PostScript                         id-ct-postscript

   The object identifiers associated with the content types listed above
   table are:

      id-ct OBJECT IDENTIFIER ::= { iso(1) member-body(2)
           us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) 1 }

      id-ct-asciiTextWithCRLF OBJECT IDENTIFIER ::= { id-ct 27 }

      id-ct-utf8TextWithCRLF OBJECT IDENTIFIER ::= { id-ct 37 }

      id-ct-htmlWithCRLF OBJECT IDENTIFIER ::= { id-ct 38 }

      id-ct-epub OBJECT IDENTIFIER ::= { id-ct 39 }

      id-ct-xml OBJECT IDENTIFIER ::= { id-ct 28 }

      id-ct-pdf OBJECT IDENTIFIER ::= { id-ct 29 }

      id-ct-postscript OBJECT IDENTIFIER ::= { id-ct 30 }

4.  Need for Canonicalization

   In general, the content of an Internet-Draft is treated like a single
   octet string for the generation of the digital signature.
   Unfortunately, the text and HTML files require canonicalization to
   avoid signature validation problems.  The primary concern is the
   manner in which different operating systems indicate the end of a
   line of text.  Some systems use a single new-line character, other
   systems use the combination of the carriage-return character followed
   by a line-feed character, and other systems use fixed-length records
   padded with space characters.  For the digital signature to validate
   properly, a single convention must be employed.

4.1.  ASCII, UTF-8, and HTML File Canonicalization

   The canonicalization procedure follows the conventions used for text
   files in the File Transfer Protocol (FTP) [FTP].  Such files must be
   supported by FTP implementations, so code reuse seems likely.

   The canonicalization procedure converts the data from its internal
   character representation to the standard 8-bit NVT-ASCII
   representation (see TELNET [TELNET]).  In accordance with the NVT
   standard, the <CRLF> sequence MUST be used to denote the end of a
   line of text.  Using the standard NVT-ASCII representation means that
   data MUST be interpreted as 8-bit bytes.

   Trailing space characters MUST NOT appear on a line of text.  That
   is, the space character must not be followed by the <CRLF> sequence.

   Thus, a blank line is represented solely by the <CRLF> sequence.

   The form-feed nonprintable character (0x0C) is expected in Internet-
   Drafts.  Other non-printable characters, such as tab and backspace,
   are not expected, but they do occur.  Non-printable or non-ASCII
   characters (ones outside the range 0x20 to 0x7E) MUST NOT be changed
   in any way not covered by the rules for end-of-line handling in the
   previous paragraph.

   Trailing blank lines MUST NOT appear at the end of the file.  That
   is, the file must not end with multiple consecutive <CRLF> sequences.

   In some environments, a Byte Order Mark (BOM) (U+FEFF) is used at the
   beginning of a file to indicate that it contains non-ASCII
   characters.  In UTF-8 or HTML files, a BOM at the beginning of the
   file is not considered to be part of the file content.  One or more
   consecutive leading BOMs, if present, MUST NOT be processed by the
   digital signature algorithm.

   Any end-of-file marker used by an operating system is not considered
   to be part of the file content.  When present, such end-of-file
   markers MUST NOT be processed by the digital signature algorithm.

   Note: This text file canonicalization procedure is consistent with
   the NVT-ASCII definition offered in Appendix B of RFC 5198 [UFNI].

4.2.  XML File Canonicalization

   Utilities that produce XML files are expected to follow the guidance
   provided by the World Wide Web Consortium (W3C) in Section 2.11 of
   [R20081126].  If this guidance is followed, no canonicalization is
   needed.

   A robust signature generation process MAY perform canonicalization to
   ensure that the W3C guidance has been followed.  This guidance says
   that a <LF> character MUST be used to denote the end of a line of
   text within an XML file.  Therefore, any two-character <CRLF>
   sequence and any <CR> that is not followed by <LF> are to be
   translated to a single <LF> character.

4.3.  No Canonicalization of Other File Formats

   No canonicalization is needed for file formats currently used or
   planned for Internet-Drafts other than ASCII, UTF-8, HTML, and XML
   files.  Other file formats, including PDF [PDF], PostScript [PS], and
   EPUB [EPUB] are treated as a simple sequence of octets by the digital
   signature algorithm.

5.  IANA Considerations

   IANA has registered object identifiers for three content types in the
   "SMI Security for S/MIME CMS Content Type (1.2.840.113549.1.9.16.1)"
   registry as follows:

   Description             OID                         Specification
   -----------------------------------------------------------------
   id-ct-utf8TextWithCRLF  1.2.840.113549.1.9.16.1.37  [RFC8358]
   id-ct-htmlWithCRLF      1.2.840.113549.1.9.16.1.38  [RFC8358]
   id-ct-epub              1.2.840.113549.1.9.16.1.39  [RFC8358]

6.  Security Considerations

   The security considerations in RFC 5485 [IDSIG] are unchanged.

7.  Deployment and Operational Considerations

   The deployment considerations in RFC 5485 [IDSIG] are unchanged.

8.  References

8.1.  Normative References

   [CMS]      Housley, R., "Cryptographic Message Syntax (CMS)", STD 70,
              RFC 5652, DOI 10.17487/RFC5652, September 2009,
              <https://www.rfc-editor.org/info/rfc5652>.

   [EPUB]     International Digital Publishing Forum, "EPUB Content
              Documents 3.1", January 2017,
              <http://www.idpf.org/epub/31/spec/epub-contentdocs.html>.

   [IDSIG]    Housley, R., "Digital Signatures on Internet-Draft
              Documents", RFC 5485, DOI 10.17487/RFC5485, March 2009,
              <https://www.rfc-editor.org/info/rfc5485>.

   [PDF]      International Organization for Standardization, "Document
              management -- Electronic document file format for long-
              term preservation -- Part 3: Use of ISO 32000-1 with
              support for embedded files (PDF/A-3)", ISO 19005-3:2012,
              2012.

   [PS]       Adobe Systems Incorporated, "PostScript Language Reference
              Manual, third edition", Addison-Wesley Publishing Company,
              ISBN 0-201-37922-8, 1999.

   [R20081126]
              Bray, T., Paoli, J., Sperberg-McQueen, M., Maler, E., and
              F. Yergeau, "Extensible Markup Language (XML) 1.0 (Fifth
              Edition)", World Wide Web Consortium Recommendation
              REC-xml-20081126, November 2008,
              <http://www.w3.org/TR/2008/REC-xml-20081126>.

   [STDWORDS] Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [STDWORDS2]
              Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [X.680]    ITU-T, "Information Technology - Abstract Syntax Notation
              One: Specification of Basic Notation",
              Recommendation X.680, ISO/IEC 8824-1:2002, 2002.

   [X.690]    ITU-T, "Information technology -- ASN.1 encoding rules:
              Specification of Basic Encoding Rules (BER), Canonical
              Encoding Rules (CER) and Distinguished Encoding Rules
              (DER)", ITU-T Recommendation X.690, ISO/IEC International
              Standard 8825-1:2008, November 2008.

8.2.  Informative References

   [FTP]      Postel, J. and J. Reynolds, "File Transfer Protocol",
              STD 9, RFC 959, DOI 10.17487/RFC0959, October 1985,
              <https://www.rfc-editor.org/info/rfc959>.

   [MSG]      Ramsdell, B. and S. Turner, "Secure/Multipurpose Internet
              Mail Extensions (S/MIME) Version 3.2 Message
              Specification", RFC 5751, DOI 10.17487/RFC5751, January
              2010, <https://www.rfc-editor.org/info/rfc5751>.

   [RFCED]    Flanagan, H., Ed., "The Use of Non-ASCII Characters in
              RFCs", RFC 7997, DOI 10.17487/RFC7997, December 2016,
              <https://www.rfc-editor.org/info/rfc7997>.

   [RFCSERIES]
              Flanagan, H. and N. Brownlee, "RFC Series Format
              Requirements and Future Development", RFC 6949,
              DOI 10.17487/RFC6949, May 2013,
              <https://www.rfc-editor.org/info/rfc6949>.

   [TELNET]   Postel, J. and J. Reynolds, "Telnet Protocol
              Specification", STD 8, RFC 854, DOI 10.17487/RFC0854,
              May 1983, <https://www.rfc-editor.org/info/rfc854>.

   [UFNI]     Klensin, J. and M. Padlipsky, "Unicode Format for Network
              Interchange", RFC 5198, DOI 10.17487/RFC5198, March 2008,
              <https://www.rfc-editor.org/info/rfc5198>.

Acknowledgements

   The idea for the Internet-Draft signature file came from a discussion
   with Scott Bradner at IETF 69 in Chicago, IL, USA.  Many helpful
   suggestions came from Jim Schaad, Pasi Eronen, Chris Newman, and Glen
   Barney.  Glen Barney also played a key role in implementing Internet-
   Draft signatures as specified in RFC 5485 [IDSIG].

Author's Address

   Russell Housley
   Vigil Security, LLC
   918 Spring Knoll Drive
   Herndon, VA 20170
   United States of America

   Email: housley@vigilsec.com