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) 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 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. Housley [Page 1] INTERNET DRAFT August 2004 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 Housley [Page 2] INTERNET DRAFT August 2004 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 Housley [Page 3] INTERNET DRAFT August 2004 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, Housley [Page 4] INTERNET DRAFT August 2004 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. 8 Author's Address Russell Housley Vigil Security, LLC 918 Spring Knoll Drive Herndon, VA 20170 USA housley@vigilsec.com Housley [Page 5] INTERNET DRAFT August 2004 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 Housley [Page 6] INTERNET DRAFT August 2004 Full Copyright Statement Copyright (C) The Internet Society (2004). All Rights Reserved. This document and translations of it may be copied and furnished to others, and derivative works that comment on or otherwise explain it or assist in its implementation may be prepared, copied, published and distributed, in whole or in part, without restriction of any kind, provided that the above copyright notice and this paragraph are included on all such copies and derivative works. However, this document itself may not be modified in any way, such as by removing the copyright notice or references to the Internet Society or other Internet organizations, except as needed for the purpose of developing Internet standards in which case the procedures for copyrights defined in the Internet Standards process must be followed, or as required to translate it into languages other than English. This document and the information contained herein is provided on an "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING TASK FORCE DISCLAIMS 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. Housley [Page 7]