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Network Working Group                                        R. HousleyRequest for Comments: 4049                               Vigil SecurityCategory: Experimental                                       April 2005BinaryTime:An Alternate Format for Representing Date and Time in ASN.1Status of This Memo   This memo defines an Experimental Protocol for the Internet   community.  It does not specify an Internet standard of any kind.   Discussion and suggestions for improvement are requested.   Distribution of this memo is unlimited.Copyright Notice   Copyright (C) The Internet Society (2005).Abstract   This document specifies a new ASN.1 type for representing time:   BinaryTime.  This document also specifies an alternate to the   signing-time attribute for use with the Cryptographic Message Syntax   (CMS) SignedData and AuthenticatedData content types; the binary-   signing-time attribute uses BinaryTime.  CMS and the signing-time   attribute are defined inRFC 3852.1.  Introduction   This document specifies a new ASN.1 [ASN1] type for representing   time:  BinaryTime.  This ASN.1 type can be used to represent date and   time values.   This document also specifies an alternative to the signing-time   attribute used with the Cryptographic Message Syntax (CMS) [CMS]   SignedData and AuthenticatedData content types, allowing the   BinaryTime type to be used instead of the traditional UTCTime and   GeneralizedTime types.1.1.  BinaryTime   Many operating systems represent date and time as an integer.  This   document specifies an ASN.1 type for representing date and time in a   manner that is also an integer.  Although some conversion may be   necessary due to the selection of a different epoch or a different   granularity, an integer representation has several advantages over   the UTCTime and GeneralizedTime types.Housley                       Experimental                      [Page 1]

RFC 4049                       BinaryTime                     April 2005   First, a BinaryTime value is smaller than either a UTCTime or a   GeneralizedTime value.   Second, in some operating systems, the value can be used with little   or no conversion.  Conversion, when it is needed, requires only   straightforward computation.  If the endian ordering is different   from the ASN.1 representation of an INTEGER, then straightforward   manipulation is needed to obtain an equivalent integer value.  If the   epoch is different than the one chosen for BinaryTime, addition or   subtraction is needed to compensate.  If the granularity is something   other than seconds, then multiplication or division is needed to   compensate.  Also, padding may be needed to convert the variable-   length ASN.1 encoding of INTEGER to a fixed-length value used in the   operating system.   Third, date comparison is very easy with BinaryTime.  Integer   comparison is easy, even when multi-precision integers are involved.   Date comparison with UTCTime or GeneralizedTime can be complex when   the two values to be compared are provided in different time zones.   This is a rare instance which both memory and processor cycles can be   saved.1.2.  Binary Signing Time Attribute   The signing-time attribute is defined in [CMS].  The alternative   binary-signing-time attribute is defined in this document in order 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 (0..MAX)Housley                       Experimental                      [Page 2]

RFC 4049                       BinaryTime                     April 2005   The integer value is the number of seconds, excluding leap seconds,   after midnight UTC, 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.  Time values beyond 03:14:07 on January 19, 2038, are   represented by integer values that are longer than four octets, and a   five-octet integer value is sufficient to represent dates covering   the next seventeen millennia.   This specification uses a variable-length encoding of INTEGER.  This   permits any time value after midnight UTC, January 1, 1970, to be   represented.   When encoding an integer value that consists of more than one octet,   which includes almost all 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; however, 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 ::= BinaryTimeHousley                       Experimental                      [Page 3]

RFC 4049                       BinaryTime                     April 2005   In [CMS], the SignedAttributes syntax and the AuthAttributes syntax   are each defined as a SET OF Attributes.  However, the 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   AuthenticatedData MUST NOT include multiple instances of the binary-   signing-time attribute.   No requirement is imposed concerning the correctness of the signing   time itself, 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 (CMS)",RFC3852, July 2004.   [STDWORDS] Bradner, S., "Key words for use in RFCs to Indicate              Requirement Levels",BCP 14,RFC 2119, March 1997.4.2.  Informative References   [TSP]      Adams, C., Cain, P., Pinkas, D., and R. Zuccherato,              "Internet X.509 Public Key Infrastructure Time-Stamp              Protocol (TSP)",RFC 3161, August 2001.5.  Security Considerations   Use of the binary-signing-time attribute does not necessarily provide   confidence in the time when 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.Housley                       Experimental                      [Page 4]

RFC 4049                       BinaryTime                     April 2005   The original signing-time attribute defined in [CMS] has the same   semantics as the binary-signing-time attribute specified in this   document.  Therefore, only one of these attributes SHOULD be present   in the signedAttrs of a SignerInfo object or in the authAttrs of an   AuthenticatedData object.  However, if both of these attributes are   present, they MUST provide the same date and time.Housley                       Experimental                      [Page 5]

RFC 4049                       BinaryTime                     April 2005Appendix 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 (0..MAX)   -- 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   ENDAuthor's Address   Russell Housley   Vigil Security, LLC   918 Spring Knoll Drive   Herndon, VA 20170   USA   EMail: housley@vigilsec.comHousley                       Experimental                      [Page 6]

RFC 4049                       BinaryTime                     April 2005Full Copyright Statement   Copyright (C) The Internet Society (2005).   This document is subject to the rights, licenses and restrictions   contained inBCP 78, and except as set forth therein, the authors   retain all their rights.   This document and the information contained herein are provided on an   "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS   OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET   ENGINEERING TASK FORCE DISCLAIM 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.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://www.ietf.org/ipr.   The IETF invites any interested party to bring to its attention any   copyrights, patents or patent applications, or other proprietary   rights that may cover technology that may be required to implement   this standard.  Please address the information to the IETF at ietf-   ipr@ietf.org.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Housley                       Experimental                      [Page 7]