Subject: I-D Action:draft-otis-dkim-adsp-sec-issues-03.txt

From: [email-masked]
Date: Tue, 30 Sep 2008 16:30:01 -0700 (PDT)

A New Internet-Draft is available from the on-line Internet-Drafts directories.

	Title           : DKIM Author Domain Signing Practices (ADSP) Security Issues
	Author(s)       : D. Otis
	Filename        : draft-otis-dkim-adsp-sec-issues-03.txt
	Pages           : 18
	Date            : 2008-09-30

The proposed [I-D.ietf-dkim-ssp] defines DNS records that advertise
the extent to which a domain employs [RFC4871] to sign [RFC2822]
messages, and defines how other hosts can access these
advertisements.  Its laudable goal is to allow domains control over
the use of the From header field.  When a message is not adequately
signed, advertised assertions, referenced by a domain in the From
header field, assist in resolving the message's intended disposition.

Rather than dealing with keys that impose a restriction on the "on-
behalf-of" identity as a separate security consideration to be
handled independently from an assertion that a domain signs their
messages, [I-D.ietf-dkim-ssp] instead employs a flawed two-stage
signature validation process that works in conjunction with
advertised practices.  The two-stage approach will most likely occur
after message acceptance, and impairs the range of authentication
assertions permitted by a single signature.  The limitations on
authentication assertions inhibits tactics needed to deal with replay
abuse.

As currently structured, advertised practices not only assert whether
a signature should be expected, they also constrain the
"on-behalf-of" identity applied by signing agents that are not
otherwise so restricted by [RFC4871].  By constraining the "on-
behalf-of" identity for all signing agents, the draft neglects the
predominate role of the domain as a point of trust, and incorrectly
assumes the signature is limited to supporting assertions regarding
the identity of the author.  By limiting the DKIM signature's "on-
behalf-of" value to being representative of only the message's
author, the draft goes well beyond the working group's charter and
appears to infringe on S/MIME's and OpenPGP's role.

[I-D.ietf-dkim-ssp] impairs security in other ways as well, such as
the only directly actionable practice is defined using a term likely
to negatively impact the integrity of delivery status.  Fortunately
minor changes to the definition of a compliant signature can remedy
the impairment created, where the critical security issues are best
handled independent of any [I-D.ietf-dkim-ssp] assertion.

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-otis-dkim-adsp-sec-issues-03.txt

Internet-Drafts are also available by anonymous FTP at:
ftp://ftp.ietf.org/internet-drafts/

Below is the data which will enable a MIME compliant mail reader
implementation to automatically retrieve the ASCII version of the
Internet-Draft.
_______________________________________________
I-D-Announce mailing list
[email-masked]
https://www.ietf.org/mailman/listinfo/i-d-announce
Internet-Draft directories: http://www.ietf.org/shadow.html
or ftp://ftp.ietf.org/ietf/1shadow-sites.txt