Internet DRAFT - draft-santos-dkim-strip
draft-santos-dkim-strip
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
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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.
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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
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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:
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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)
<CR> (OCTET 13) Carriage Return
<LF> (OCTET 10) Line Feed
<TSP> (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.
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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, <http://mipassoc.org/dkim/specs/
draft-allman-dkim-base-04.html>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
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[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,
<http://www.dlib.org/dlib/september99/09lynch.html>.
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
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