Internet-Draft D. Del Torto OpenPGP Working Group CryptoRights Foundation draft-ietf-openpgp-multsig-01.txt R. Levien University of California at Berkeley T. Roessler August 2000 Multiple Signatures using Security Multiparts Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. 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 as "work in progress." The list of current Internet-Drafts can be accessed at . The list of Internet-Draft Shadow Directories can be accessed at . Copyright (c) The Internet Society 2000. All Rights Reserved. Abstract This document describes how the Security Multiparts defined in RFC 1847 [1] can be used to transport multiple digital signatures. This draft is being discussed on the "ietf-openpgp" mailing list. To join the list, send a message to with the single word "subscribe" in the subject. A web site containing an archive of the list can be found at . Del Torto, et al. Expires February 2001 [Page 1] INTERNET-DRAFT Multiple Signatures August 2000 1. Introduction Various digital signature services for electronic mail rely on the framework defined in RFC 1847. These signature services do not address the issue of parallel signatures on the same content. Instead of specifying parallel signature formats for individual signature services such as OpenPGP, the present document defines a "multipart/mixed" protocol for the "multipart/signed" body type introduced in RFC 1847. The "multipart/mixed" protocol permits users to bundle parallel signatures for the same content into one "multipart/signed" body part. It is independent of the protocols used to form the individual digital signatures. 1.1. Compliance In order for an implementation to be compliant with this specification, is it absolutely necessary for it to obey all items labeled as MUST or REQUIRED. 2. The "multipart/mixed" protocol 2.1. Specification Digitally signed messages conforming to this document are denoted by the "multipart/signed" content type, defined in RFC 1847, with a "protocol" parameter which MUST have a value of "multipart/mixed". (MUST be quoted). The "micalg" parameter MUST contain a comma-separated list of hash- symbols. These hash-symbols identify the message integrity check (MIC) algorithm(s) used to generate the subsequent signature(s). Hash-symbols MUST NOT occur more than once in this list. The multipart/signed body MUST consist of exactly two parts. The first part contains the signed data in MIME canonical format, including a set of appropriate content headers describing the data. The second part MUST be of type "multipart/mixed". Each sub-part represents an individual digital signature which has been formed according to RFC 1847 and the specification of the signature protocol used. Del Torto, et al. Expires February 2001 [Page 2] INTERNET-DRAFT Multiple Signatures August 2000 2.2. Example message From: Dave Del Torto To: Raph Levien Mime-Version: 1.0 Content-Type: multipart/signed; protocol="multipart/mixed"; boundary=0000_031; micalg="pgp-sha1, rsa-md5, pgp-md5" --0000_031 Content-Type: text/plain Hi Raph, Here's some text with parallel (multiple) digital signatures in various formats. dave ______________________________________________________________________ "All email luxuriantly hand-crafted using only the finest ASCII text." --0000_031 Content-Type: multipart/mixed; boundary=0000_032 --0000_032 Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: PGP for Personal Privacy 5.0 Comment: Hash computed using SHA-1 micalg (FIPS 180-1). iQCVAwUBM0It9qHBOF9KrwDlAQFBaQQAisIzQUgyknT2v729b7MImcUc3ROdRBh6 nwMyAfdewQYCDxqdDWvnD1UWoUjwjA1JNA6qhTXBxs8yPtZdDZaguOG2zWawyat9 Jib556AuSx10psREDC3vNsaJ99MV8SKFF92H53l9w/YhVOA0aMZeNfLE0jJVypkY /so4/7DHhqQ= =/wlj -----END PGP SIGNATURE----- --0000_032 Content-Type: application/x-pkcs7-signature Content-Transfer-Encoding: base64 Comment: Hash computed using S/MIME MD5 micalg. MIAGCSqGSIb3DQEHAqCAMIACAQExDjAMBggqhkiG9w0CBQUAMIAGCSqGSIb3DQEH [signature material removed] Del Torto, et al. Expires February 2001 [Page 3] INTERNET-DRAFT Multiple Signatures August 2000 +kNIWIbxNiNje1wlzIhaGjrGrOnvYc8+tFn2LgAAAAAAAAAA --0000_032 Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: PGP 2.6.2 Comment: Hash computed using MD5 micalg. iQCVAwUBM0Iu16HBOF9KrwDlAQGaiQP9EU1YXgMSoNxDAqSmo7UoCE52DuYCfxm7 x8RfRr9+Xz3nPFytSYM2TIWGMeKi1fVr5PhfjdrKvOh9sCq97h6zndZVpGA9x62k mPVn/QY3fz1eOdyJbYvW4ba7WQll5OoA6cqmEb9tWwh4ra4yE8hZMnLS9a0uPpuB 5dpiTTAE/gY= =hD3D -----END PGP SIGNATURE----- --0000_032-- --0000_031-- 3. Security Considerations Use of this protocol has the same security considerations as RFC 1847 and the individual digital signature protocols used. It is not known to either increase or decrease the security of messages using it. Users should be aware of the fact that each individual signature can be broken out and used to create a valid "multipart/signed" body according to the underlying protocol and RFC 1847. 4. Acknowledgements We thank Jim Galvin, Sandy Murphy, Steve Crocker, and Ned Freed for their pioneering work on security using MIME multiparts, on which the refinement specified in this document is based. This draft document relies on the work of the IETF's OpenPGP Working Group. 5. Addresses of the Authors and OpenPGP Working Group Chair The OpenPGP working group can be contacted via the current chair: John W. Noerenberg, II Qualcomm, Inc. 5775 Morehouse Dr. San Diego, CA 92121 USA Email: jwn2@qualcomm.com Del Torto, et al. Expires February 2001 [Page 4] INTERNET-DRAFT Multiple Signatures August 2000 The principal authors of this draft are: Dave Del Torto CryptoRights Foundation 80 Alviso Street, Mailstop: CRF San Francisco, CA 94127 USA Tel: +1 415 334 5533 Email: ddt@cryptorights.org, ddt@openpgp.net Raph Levien University of California at Berkeley 579 Soda Hall Berkeley, CA 94720 USA Tel: +1 510 642 6509 Email: raph@acm.org Thomas Roessler Nordstrasse 99 D-53111 Bonn Germany Tel.: +49 228 638007 Email: roessler@does-not-exist.org References [1] Galvin, J., Murphy, G., Crocker, S., and N. Freed, "Security Multiparts for MIME: Multipart/Signed and Multipart/Encrypted", RFC 1847, October 1995. [2] Galvin, J., Murphy, G., Crocker, S., and N. Freed, "MIME Object Security Services", RFC 1848, October 1995. [3] Callas, J., Donnerhacke, L., Finney, H., Thayer, R., "OpenPGP Message Format", RFC 2440, November 1998. [4] Elkins, M., "MIME Security with Pretty Good Privacy (PGP)", RFC 2015, October 1996. Full Copyright Notice Copyright (c) The Internet Society 2000. 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 Del Torto, et al. Expires February 2001 [Page 5] INTERNET-DRAFT Multiple Signatures August 2000 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. The limited permissions granted above are perpetual and will not be revoked by the Internet Society or its successors or assigns. 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. Del Torto, et al. Expires February 2001 [Page 6]