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

From: "Hallam-Baker, Phillip" <[email-masked]>
Date: Thu, 6 Apr 2006 13:44:32 -0700

It certainly appears to be a policy issue and thus out of scope for PKIX.

CAs that issue certs with domain names in them should be aware of I18N and
the possible effect of that on the assurances in the CPS. So there is a
possible Security Consideration entry.

> -----Original Message-----
> From: [email-masked] 
> [mailto:[email-masked]] On Behalf Of Andrews, Rick
> Sent: Thursday, April 06, 2006 2:10 PM
> To: Kurt D. Zeilenga; Denis Pinkas
> Cc: [email-masked]; [email-masked]
> Subject: RE: Last Call: 'Update to DirectoryString Processing 
> in the Internet X.509PublicKey Infrastructure Certificate and 
> Certificate RevocationList
> 
> 
> Kurt,
> 
> I don't agree that it's really a CA issue. The CA verifies 
> that the company requesting the certificate owns the domain 
> name and optionally the Organization name that will appear in 
> the cert. If the company legitimately purchased the domain 
> name, they should be able to get a certificate. I would argue 
> that it's the responsibility of the domain name registrar or 
> registry to filter out domain requests that are misleading. A 
> phisher can mount an attack without using an SSL certificate. 
> That's why the Unicode Consortium, in Unicode Technical 
> Report #36 (Unicode Security Considerations), described 
> recommendations for domain registrars and registries.
> (http://www.unicode.org/draft/reports/tr36/tr36.html)
> 
> -Rick
> 
> > -----Original Message-----
> > From: [email-masked]
> > [mailto:[email-masked]] On Behalf Of Kurt D. Zeilenga
> > Sent: Thursday, April 06, 2006 8:31 AM
> > To: Denis Pinkas
> > Cc: [email-masked]; [email-masked]
> > Subject: Re: Last Call: 'Update to DirectoryString 
> Processing in the 
> > Internet X.509PublicKey Infrastructure Certificate and Certificate 
> > RevocationList
> > 
> > 
> > At 06:07 AM 4/6/2006, Denis Pinkas wrote:
> > >Mandating the use UTF8 was/is an error, because it is a
> > major security
> > >threat and that error should be corrected ASAP.
> > 
> > I disagree that this mandate is in error.  I disagree that 
> its a major 
> > security threat.  And I disagree that printableString significantly 
> > reduces the spoofing threat.
> > One can generally create spoofs of one printableString using only 
> > printableString.
> > 
> > As Stefan pointed out, this is really a CA issue.  Users 
> who choose to 
> > trust a CA, choose to trust that the CA is taking appropriate steps 
> > not to allow one to obtain a certificate that appears that 
> it belongs 
> > to another.
> > 
> > I would however agree that the document should not be silent on the 
> > subject.  It should state something like:
> >    Two different character strings can easily appear (in
> >    common and/or a particular font) to be the same string and
> >    hence CAs should have and follow appropriate policies to
> >    reduce as to who is the subject of any certificate they issue.
> > 
> > Note that I didn't mention Unicode in my suggestion.  As 
> noted above, 
> > the spoofing problem is not limited to Unicode.
> > 
> > - Kurt
> > 
> > 
> > 
> > >Denis
> > >
> > >>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-ut
> > f8-02.txt
> > >>
> > >>
> > >>
> > >>
> > >>
> > >
> > >Regards,
> > >
> > >Denis Pinkas
> > 
> > 
> > 
> 
> 
>