Network Working Group R. Housley Internet Draft Vigil Security expires in six months September 2004 BinaryTime: An alternate format for representing date and time in ASN.1 Status of this Memo By submitting this Internet-Draft, I certify that any applicable patent or other IPR claims of which I am aware have been disclosed, or will be disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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 a "work in progress." The list of current Internet-Drafts can be accessed at http://www.ietf.org/1id-abstracts.html The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html This Internet-Draft is expected to be published as an Experimental RFC. Abstract This document specifies a new ASN.1 type for representing time: BinaryTime. This document also specifies an alternate signing-time attribute for use with the Cryptographic Message Syntax (CMS) SignedData content type that permits the use of BinaryTime. CMS and the signing-time attribute are defined in RFC 3852. Housley [Page 1] INTERNET DRAFT September 2004 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 updates signing-time attribute used with the Cryptographic Message Syntax (CMS) [CMS] SignedData content type, allowing BinaryTime to be used. 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. The operating systems that do require conversion can do so with straightforward computation. 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 where both memory and processor cycles are saved. 1.2 Binary Signing Time Attribute The signing-time attribute is defined in [CMS]. The updated signing- time attribute is defined in this document to obtain the benefits of the BinaryTime type, while maintaining backward compatibility with the original signing-time attribute specification. 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]. Housley [Page 2] INTERNET DRAFT September 2004 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. Time values beyond 03:14:07 on January 19, 2038 are represented by integer values that are longer than four octets. This specification uses a variable length encoding of INTEGER. This permits any time value after midnight, January 1, 1970 to be 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 Revised Signing Time Attribute Definition A new object identifier is assigned to the revised signing-time attribute. In this way, an implementation that supports the signing- time attribute but does not support this revision will not encounter any difficulty since unrecognized CMS attributes are ignored. Like the original signing-time attribute, the updated signing-time attribute type specifies the time at which the signer (purportedly) performed the signing process. The updated 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 updated signing-time attribute MUST be a signed attribute or an authenticated attribute; it MUST NOT be an unsigned attribute, unauthenticated attribute, or unprotected attribute. Housley [Page 3] INTERNET DRAFT September 2004 The following object identifier identifies the updated signing-time attribute: id-aa-signingTime2 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) aa(2) 46 } The updated signing-time attribute values have ASN.1 type SigningTime2: SigningTime2 ::= CHOICE { utcTime UTCTime, generalizedTime GeneralizedTime, binaryTime BinaryTime } In [CMS], the SignedAttributes syntax and the AuthAttributes syntax are each defined as a SET OF Attributes. However, the updated 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 updated signing-time attribute. Similarly, the AuthAttributes in an AuthenticatedData MUST NOT include multiple instances of the updated 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. 3.1 utcTime Dates between January 1, 1950 and December 31, 2049 (inclusive) can be represented using the utcTime alternative. Any dates with year values before 1950 or after 2049 MUST be encoded using either generalizedTime or binaryTime, and they MUST NOT be encoded using the utcTime alternative. Date and time values encoded using the utcTime alternative MUST be expressed in Coordinated Universal Time (UTC) and MUST include seconds (i.e., times are YYMMDDHHMMSSZ), even where the number of seconds is zero. Midnight MUST be represented as "YYMMDD000000Z". Century information is implicit, and the century MUST be determined Housley [Page 4] INTERNET DRAFT September 2004 as follows: Where YY is greater than or equal to 50, the year MUST be interpreted as 19YY; and Where YY is less than 50, the year MUST be interpreted as 20YY. 3.2 generalizedTime Date and time values encoded using the generalizedTime alternative MUST be expressed in Coordinated Universal Time (UTC) and MUST include seconds (i.e., times are YYYYMMDDHHMMSSZ), even where the number of seconds is zero. The GeneralizedTime value MUST NOT include fractional seconds. 3.2 binaryTime When the binaryTime alternative is used, date and time values MUST be expressed in Coordinated Universal Time (UTC), and the granularity of the time is seconds. It is not possible to represent a finer granularity. 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. Housley [Page 5] INTERNET DRAFT September 2004 5 Security Considerations This specification does not introduce any new security considerations beyond those already discussed in [CMS]. Use of the updated 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. The original signing-time attribute defined in [CMS] has the same semantics as the updated signing-time attribute specified in this document. If both of these attributes are present, they SHOULD provide the same date and time. 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, or will be disclosed, and any of which I become aware will be disclosed, in accordance with RFC 3668. 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 in BCP 78 and BCP 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 at http://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. Housley [Page 6] INTERNET DRAFT September 2004 8 Author's Address Russell Housley Vigil Security, LLC 918 Spring Knoll Drive Herndon, VA 20170 USA housley@vigilsec.com 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-signingTime2 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) rsadsi(113549) pkcs(1) pkcs9(9) smime(16) aa(2) 46 } SigningTime2 ::= CHOICE { utcTime UTCTime, generalizedTime GeneralizedTime, binaryTime BinaryTime } END Housley [Page 7] INTERNET DRAFT September 2004 Full Copyright Statement Copyright (C) The Internet Society (2004). All Rights Reserved. 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