DKIM Working Group H. Santos Internet-Draft Santronics Software, Inc. Intended status: Experimental July 26, 2006 Expires: January 27, 2007 DKIM Canonicalization Method: STRIP draft-santos-dkim-strip-00 Status of this Memo By submitting this Internet-Draft, each author represents that any applicable patent or other IPR claims of which he or she is aware have been or will be disclosed, and any of which he or she becomes aware will be disclosed, in accordance with Section 6 of BCP 79. 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 http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on January 27, 2007. Copyright Notice Copyright (C) The Internet Society (2006). Abstract The DKIM base protocol has offers two digital signature canonicalization (cl4n) methods called "relaxed" and "simple" with low reliability and survivability during in-transient operations. This proposal describes a new STRIP canonicalization algorithm and method to increase the reliability and survivability of the digital signature. In additional, the proposal describe new original body hashing requirements to help secure STRIP c14n security concerns found in a similar but deprecated NOFWS c14n method. Santos Expires January 27, 2007 [Page 1] Internet-Draft DSAP July 2006 To be Done List 1. Get Examples of security issues for NOFWS. 2. Complete Security Section. Table of Contents 1. Nomemclature and Definitions . . . . . . . . . . . . . . . . . 3 1.1. Requirements Language . . . . . . . . . . . . . . . . . . . 3 2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3 3. STRIP Canonicalization . . . . . . . . . . . . . . . . . . . . 4 4. Signing Logic . . . . . . . . . . . . . . . . . . . . . . . . . 4 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5 6. Security Considerations . . . . . . . . . . . . . . . . . . . . 5 6.1. Replays . . . . . . . . . . . . . . . . . . . . . . . . . . 5 6.2. Denial-of-Service Attacks . . . . . . . . . . . . . . . . . 5 7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 5 8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 5 8.1. Normative References . . . . . . . . . . . . . . . . . . . 5 8.2. Informative References . . . . . . . . . . . . . . . . . . 6 Appendix A. Appendix . . . . . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 6 Intellectual Property and Copyright Statements . . . . . . . . . . 7 Santos Expires January 27, 2007 [Page 2] Internet-Draft DSAP July 2006 1. Nomemclature and Definitions 1.1. Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in RFC 2119 [RFC2119]. 2. Introduction The DKIM [DKIM-BASE] protocol implements message canonicalization (c14n) as part its Digital Signature model. Two c14n methods are currently defined: SIMPLE RELAXED SIMPLE is the the strongest of the two to maintain the originality of the message integrity during the mail delivery process Any slight change to the message header or body content at any point during the transport will cause the verification of the signature to fail. RELAXED provides a method which canonicalizing the header and body content to a disembodied digital form with the goal to increase the survivability of the signature. Due to the nature of the current infrastructure with a high degree of unknown, the stronger SIMPLE c14n has a low survival rate. Although RELAXED improves the chances of survival of the signature, there still exist legacy CR/LF mutations that can fail the verification process. This documents introduces the new STRIP c14n which is similar to RELAXED but with the added logic to remove all CR and LF characters from the hashing engine. The STRIP c14n is very similar to the NOFWS c14n method used by Yahoo's experimental DomainKeys protocol and was once considered for usage for the DKIM protocol. However, since it was determined the NOFWS c14n exhibited some replay security threats, it is expected for STRIP c14n to also inherent the same security concerns. To address this issue and to protect the STRIP c14n, a new original body hashing signature tag is introduced to eliminate the mail integrity security concerns. The goals of this proposal are: Santos Expires January 27, 2007 [Page 3] Internet-Draft DSAP July 2006 1. help increase the validation of the signature that are now affected due to current and/or legacy infrastructure CR/LR related mutations. 2. by introducing cl4n method called STRIP, and 3. by augmented it with a original body hash security layer that will help eliminate the security concerns related to a STRIP cl4n method. 3. STRIP Canonicalization The STRIP c14n method is similar to the RELAXED c14n with the added step of removing the trailing white spaces in the hashing engine feed: (preamble) (OCTET 13) Carriage Return (OCTET 10) Line Feed (OCTET 32) Trailing Space (postamble) 4. Signing Logic If the signer wishes to use the STRIP cl4n method, follow the DKIM- BASE [DKIM-BASE] specs for signing by also incorporating the following steps: 1. Add the required tags to the DKIM-SIG header. 2. Add the "bc=strip" tag to the DKIM-SIG header. 3. Calculate the body hash (bh=) based on STRIP cl4n method. 4. Add the bh=body-hash tag to the DKIM-SIG header. 5. Calculate the signature hash (b=). 6. Add the b=sign-hash to the DKIM-SIG header. 7. Calculate the original body hash (oh=) based on SIMPLE cl4n method. 8. Add the oh=body-hash tag to the DKIM-SIG header. Santos Expires January 27, 2007 [Page 4] Internet-Draft DSAP July 2006 The following an example DKIM-Signature with STRIP c14n support: DKIM-Signature: a=rsa-sha256; s=brisbane; d=example.com; c=simple; bc=strip; q=dns/txt; i=joe@football.example.com; h=Received : From : To : Subject : Date : Message-ID; bh=ZSVEYuq4ri3LR9S+qjlzCP+LxvJrIfrOI2g5hxp5+MI=; b=dzdVyOfAKCdLXdJOc9G2q8LoXSlEniSbav+yuU4zGeeruD00lszZVoG4ZHRNiYzR; oh=ADasdadaasdada-adsad123-2n123d+232x1ahddlld=; 5. IANA Considerations This document makes no request of IANA. Note to RFC Editor: this section may be removed on publication as an RFC. 6. Security Considerations 6.1. Replays TBD 6.2. Denial-of-Service Attacks TBD 7. Acknowledgements Discussions related to canonicalization in the IETF-DKIM Working Group among many participants lead to the development of this proposed draft. 8. References 8.1. Normative References [DKIM-BASE] Allman, E., "DomainKeys Identified Mail Signatures", April 2006, . [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997. Santos Expires January 27, 2007 [Page 5] Internet-Draft DSAP July 2006 [RFC2821] Klensin, J., "Simple Mail Transfer Protocol", RFC 2821, April 2001. [RFC2822] Resnick, P., "Internet Message Format", RFC 2822, April 2001. 8.2. Informative References [LYNCH] Lynch, C., "Canonicalization: A Fundamental Tool to Facilitate Preservation and Management of Digital Information", 1999, . Appendix A. Appendix Author's Address Hector Santos Santronics Software, Inc. 15600 SW 158 ST Suite #306 Homestead, Florida, FL 33033 United States of America Email: hsantos@isdg.net URI: http://www.isdg.net Santos Expires January 27, 2007 [Page 6] Internet-Draft DSAP July 2006 Full Copyright Statement Copyright (C) The Internet Society (2006). This document is subject to the rights, licenses and restrictions contained in BCP 78, and except as set forth therein, the authors retain all their rights. 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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. Acknowledgment Funding for the RFC Editor function is provided by the IETF Administrative Support Activity (IASA). Santos Expires January 27, 2007 [Page 7]