Network Working Group                                        R. Housley
Internet Draft                                           Vigil Security
expires in six months                                       August 2004


                          Binary Signing Time:
 A Signed Attribute for use with the Cryptographic Message Syntax (CMS)

                   <draft-housley-binarytime-00.txt>


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   patent or other IPR claims of which I am aware have been disclosed,
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Abstract

   This document specifies a new ASN.1 type for representing time:
   BinaryTime.  This document also specifies the binary-signing-time
   attribute for use with the Cryptographic Message Syntax (CMS)
   SignedData content type.  CMS is defined in RFC 3852.

1  Introduction

   This document specifies a new ASN.1 [ASN1] type for representing
   time: BinaryTime.  This document also specifies the binary-signing-
   time attribute for use with the Cryptographic Message Syntax (CMS)
   [CMS] SignedData content type that makes use of the BinaryTime type.




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1.1  BinaryTime

   Many operating systems represent date and time as an integer.  This
   document specifies an ASN.1 type for representing a date and time in
   a manner that is compatible with these operating systems.  This
   approach has several advantages over the UTCTime and GeneralizedTime
   types.

   First, a BinaryTime value is smaller than either a UTCTime or a
   GeneralizedTime value.

   Second, in many operating systems, the value can be used without
   conversion.

   This is a rare instance where both memory and processor cycles are
   saved.

1.2  Binary Signing Time Attribute

   The signing-time attribute is defined in [CMS].  The binary-signing-
   time attribute is defined in this document to obtain the benefits of
   the BinaryTime type.

1.3  Terminology

   In this document, the key words MUST, MUST NOT, REQUIRED, SHOULD,
   SHOULD NOT, RECOMMENDED, MAY, and OPTIONAL are to be interpreted as
   described in [STDWORDS].

2  BinaryTime Definition

   The BinaryTime ASN.1 type is used to represent an absolute time and
   date.  A positive integer value is used to represent time values
   based on coordinated universal time (UTC), which is also called
   Greenwich Mean Time (GMT) and ZULU clock time.

   The syntax for BinaryTime is:

      BinaryTime ::= INTEGER

   The integer value is the number of seconds after midnight, January 1,
   1970.  This time format cannot represent time values prior to January
   1, 1970.  The latest UTC time value that can be represented by a
   four-octet integer value is 03:14:07 on January 19, 2038, which is
   represented by the hexadecimal value 7FFFFFFF.

   This specification uses a variable length encoding of INTEGER.  This
   permits any time value after midnight, January 1, 1970 to be



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   represented.

   When encoding of an integer value that consists of more than one
   octet, which includes almost all of the time values of interest, the
   bits of the first octet and bit 8 of the second octet MUST NOT all be
   ones or all zeros.  This rule ensures that an integer value is always
   encoded in the smallest possible number of octets.  However, it means
   that implementations cannot assume a fixed length for the integer
   value.

3  Binary Signing Time Attribute Definition

   The binary-signing-time attribute type specifies the time at which
   the signer (purportedly) performed the signing process.  The binary-
   signing-time attribute type is intended for use in the CMS SignedData
   content type.  The attribute can also be used with the
   AuthenticatedData content type.

   The binary-signing-time attribute MUST be a signed attribute or an
   authenticated attribute; it MUST NOT be an unsigned attribute,
   unauthenticated attribute, or unprotected attribute.

   The following object identifier identifies the binary-signing-time
   attribute:

      id-aa-binarySigningTime OBJECT IDENTIFIER ::= { iso(1)
          member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
          smime(16) aa(2) 46 }

   The binary-signing-time attribute values have ASN.1 type
   BinarySigningTime:

      BinarySigningTime ::= BinaryTime

   By using the BinaryTime type, BinarySigningTime values MUST be
   expressed in Coordinated Universal Time (formerly known as Greenwich
   Mean Time (GMT) and Zulu clock time), and the granularity of the time
   is seconds.  It is not possible to represent a finer granularity.

   In [CMS], the SignedAttributes syntax and the AuthAttributes syntax
   are each defined as a SET OF Attributes.  However, a binary-signing-
   time attribute MUST have a single attribute value, even though the
   syntax is defined as a SET OF AttributeValue.  There MUST NOT be zero
   or multiple instances of AttributeValue present.

   The SignedAttributes contained in the signerInfo structure within
   SignedData MUST NOT include multiple instances of the binary-signing-
   time attribute.  Similarly, the AuthAttributes in an



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   AuthenticatedData MUST NOT include multiple instances of the binary-
   signing-time attribute.

   No requirement is imposed concerning the correctness of the signing
   time, and acceptance of a purported signing time is a matter of a
   recipient's discretion.  It is expected, however, that some signers,
   such as time-stamp servers, will be trusted implicitly.

4  References

   This section provides normative and informative references.

4.1  Normative References

   ASN1       CCITT.  Recommendation X.208: Specification of Abstract
              Syntax Notation One (ASN.1).  1988.

   CMS        Housley, R.  Cryptographic Message Syntax.  RFC 3852.
              July 2004.

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

4.2  Informative References

   TSP        Adams, C., P. Cain, D. Pinkas, and R. Zuccherato.
              Internet X.509 Public Key Infrastructure Time-Stamp
              Protocol (TSP).  RFC 3161.  August 2001.

5  Security Considerations

   This specification does not introduce any new security considerations
   beyond those already discussed in [CMS].

   Use of the binary-signing-time attribute does not necessarily provide
   confidence in the time that the signature value was produced.
   Therefore, acceptance of a purported signing time is a matter of a
   recipient's discretion.  RFC 3161 [TSP] specifies a protocol for
   obtaining time stamps from a trusted entity.

6  IANA Considerations

   No IANA actions are needed.

7  IPR Considerations

   By submitting this Internet-Draft, I certify that any applicable
   patent or other IPR claims of which I am aware have been disclosed,



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   or will be disclosed, and any of which I become aware will be
   disclosed, in accordance with RFC 3668.

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8  Author's Address

   Russell Housley
   Vigil Security, LLC
   918 Spring Knoll Drive
   Herndon, VA 20170
   USA

   housley@vigilsec.com

















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Appendix A:  ASN.1 Module

   The ASN.1 module contained in this appendix defines the structures
   that are needed to implement this specification.  It is expected to
   be used in conjunction with the ASN.1 modules in [CMS].


   BinarySigningTimeModule
     { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1)
       pkcs-9(9) smime(16) modules(0) 27 }

   DEFINITIONS IMPLICIT TAGS ::=
   BEGIN


   -- BinaryTime Definition

   BinaryTime ::= INTEGER


   -- Signing Binary Time Attribute

   id-aa-binarySigningTime OBJECT IDENTIFIER ::= { iso(1)
       member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9)
       smime(16) aa(2) 46 }

   BinarySigningTime ::= BinaryTime


   END





















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Housley                                                         [Page 7]