Subject: RE: Last Call: 'Update to DirectoryString Processing in the Internet X.509Public Key Infrastructure Certificate and Certificate RevocationList

From: "Santosh Chokhani" <[email-masked]>
Date: Thu, 6 Apr 2006 07:21:10 -0700

Russ,

My posting below is agreement with your position.

-----Original Message-----
From: Russ Housley [mailto:[email-masked]] 
Sent: Thursday, April 06, 2006 9:30 AM
To: Santosh Chokhani; [email-masked]
Cc: [email-masked]
Subject: RE: Last Call: 'Update to DirectoryString Processing in the
Internet X.509Public Key Infrastructure Certificate and Certificate
RevocationList 

Santosh:

RFC 3280 says that the only encoding allowed (after December 31, 
2003) is UTF8String.  Clearly, this MUST statement was not followed 
in implementations, and the document that we are discussing updates 
RFC 3280 to allow either UTF8String or PrintableString.  If we 
discourage the use of UTF8String, then we are penalizing the folks 
that followed RFC 3280 -- that does not seem right to me.

Russ

  At 06:36 AM 4/6/2006, Santosh Chokhani wrote:

>Denis,
>
>I have been rethinking my position.  In terms of spoofing the human
>relying party using character encoding, requiring printable string when
>possible does not defeat the threat of intentionally created UTF8
string
>that is similar.  Protection of human relying parties will require
>banning UTF8 altogether.
>
>The benefit of strongly recommending or mandating printable string
where
>possible is only to those high assurance environments where the relying
>parties reject UTF8.  That benefit is not so much a security benefit,
>but interoperability benefit in terms of being able to accept more
>certificates since more certificates will be encoded as printable
>string.
>
>-----Original Message-----
>From: [email-masked]
[mailto:[email-masked]]
>On Behalf Of Denis Pinkas
>Sent: Thursday, April 06, 2006 3:52 AM
>To: [email-masked]
>Cc: [email-masked]
>Subject: Re: Last Call: 'Update to DirectoryString Processing in the
>Internet X.509Public Key Infrastructure Certificate and Certificate
>RevocationList
>
>
>To the IESG,
>
>I have strong concerns with this document.
>
>Santosh Chokhani wrote on 4/3/2006: Given the problems with UTF8 in
>terms
>of spoofing, should we not require or strongly urge the use of
printable
>string
>when printable string will suffice ?
>
>I totally agree with him.
>
>On 06/03/2006, I wrote to the PKIX mailing list:
>
>  Michel Suignard from Microsoft gave a presentation on Unicode
security
>considerations.
>  As Unicode is used in security sensitive applications, there are a
>number of ways
>  where two strings that look similar or identical can actually be
>different strings.
>  Examples include domain names and other iidentifiers. The
presentation
>discussed
>  many of the causes of these problems and gave numerous examples of
>potentially
>  confusing character combinations. The presentation also discussed the
>Unicode
>  Consortium's current best practices in avoiding these problems. The
>presentation
>  was followed by  questions:
>
>       Paul Hoffman pointed out that in addition to the Unicode
security
>issues people need to be
>       aware of encoding. The most obvious case of this is the URL
>parsing attacks where Unicode
>       escapes could be used to get around prohibited characters. Paul
>specifically mentioned cases
>       where identifiers and text in environment might use different
>encodings. Paul warned that
>       functions trying to enforce Unicode limitations might need to
>consider as many as seven
>       common encodings.
>
>       Another concern is scripts written to assume that their input is
>just octets. With US ASCII there
>       is only one way to represent characters. However if some parts
of
>a system interpret characters
>       as Unicode and some as ASCII, then problems may result. Network
>management scripts may
>       be a particular concern.
>
>       The issue of backward compatibility was discussed. The IETF is
in
>an unfortunate position
>       because in order to correct errors in normalization the Unicode
>consortium made
>       non-backward-compatible changes. These changes require us to
>decide what to do about the
>       stringprep specification. Currently, stringprep is still using
an
>old version of Unicode. Michel
>       points out that this is not an acceptable long-term solution
>because characters have been added
>       that parts of the world will want to use.
>
>       Nico Williams pointed out that there are other levels at which
>this problem exists. For example,
>       misspellings can be instances of the same problem. Also, the
ways
>in which we can fix this
>       problem are limited. For instance, we cannot add prohibited
>characters to stringprep tables.
>
>       There was a discussion of the common solutions proposed to
address
>this problem. Solutions
>       include awareness of language and awareness of characters that
do
>not normally go together.
>       None of these solutions is perfect.
>
>=======================================================================
=
>=============================
>
>Using different character sets, it is possible to have the same
*visual*
>
>representation for differents DNs when thse DNs are coded using
>UTF8String.
>
>(text deleted)
>
>RFC 3280 states:
>
>    The DN MUST be unique for each subject
>    entity certified by the one CA as defined by the issuer name field.
>
>If only this rule is maintained, then a CA could legitimately issue
>two certificates that contain two different DNs, but which have the
>same *visual* representation.
>
>:-(
>
>=======================================================================
=
>=============================
>
>I believe that it is necessary:
>
>  1) to follow the position from Santosh,
>  2) to add a section in the security considerations section to deal
with
>these aspects.
>
>Denis
>
> >The IESG has received a request from the Public-Key Infrastructure
>(X.509) WG
> >to consider the following document:
> >
> >- 'Update to DirectoryString Processing in the Internet X.509 Public
>Key
> >   Infrastructure Certificate and Certificate Revocation List (CRL)
>Profile '
> >   <draft-ietf-pkix-cert-utf8-02.txt> as a Proposed Standard
> >
> >The IESG plans to make a decision in the next few weeks, and solicits
> >final comments on this action.  Please send any comments to the
> >[email-masked] or [email-masked] mailing lists by 2006-04-12.
> >
> >The file can be obtained via
> >http://www.ietf.org/internet-drafts/draft-ietf-pkix-cert-utf8-02.txt