Subject: Problem for public CAs

From: "Graham Laws" <[email-masked]>
Date: Mon, 7 Feb 2000 14:24:16 -0000

For public CAs, particularly in Europe, the requirement to place an email
address in the subjectAltname extension of each x.509 public key certificate
in order to enable S/MIME is a big problem.

Firstly, all such certificates must reside in a public Directory. Any
determined spammer is going to be able to easily create an immense spam list
from the Directory's entire certificate population, using a few LDAP calls
and an ASN.1 decoder. Our customers are already nervous at the prospect of
this, and for potential customers it may be a significant bar to take-up.

Secondly, the European Privacy Directive looks very unfavourably upon
real-world identities being in any way expressed both in the Subject and
SubjectAltName attributes of the public key certificate. This would appear
to rule out S/MIME for those whose names are embedded in their email
addresses, e.g.  [email-masked]

The issues raised by the second point are relatively easy to circumvent. Use
pseudonymous names for the Subject, and insist on a pseudonymous email
address if S/MIME is required.

But the first point about the ease with which spam lists can be created is a
real worrier. I have looked through previous threads, including the one
entitled "Mail addresses in S/MIME certs", but I can't find where these
specific issues have been discussed before.

Comments/discussion via this forum welcome.

Best Regards
Graham Laws

______________________________________________
Graham Laws
PKI Systems Technical Consultant
Royal Mail ViaCode	Phone : 	+44 (0)1246-293761
Block A, 1st Floor	Postline : 5453-3761
St. Mary's Court		Fax : 	+44 (0)1246-293751
St. Mary's Gate
Chesterfield
S41 7TD

Public Key Validation String : MXZQ-7MM5-9A58

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From: Paul Hoffman / IMC <[email-masked]>
Date: Mon, 07 Feb 2000 10:28:31 -0800

Hmmm. Either you identify the public key in a certificate by an appropriate 
identifier (and "email address" is appropriate for S/MIME), or you ignore 
the identification in the certificate. Are you proposing an alternative 
solution for S/MIME certificate usage?

--Paul Hoffman, Director
--Internet Mail Consortium

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From: Russ Housley <[email-masked]>
Date: Wed, 09 Feb 2000 11:27:35 -0500

Graham:

Certificates usually contain a subject name and a public key.  However, 
this information is not adequate for a mail user agent to determine which 
certificate goes with a particular e-mail address.  That is why the S/MIME 
RFCs require the inclusion of the e-mail address in the subjectAltName.

Several people have tried to build S/MIME capabilities that support 
certificates without e-mail address in the subjectAltName.  The results are 
security vulnerabilities!  The address book must be used to associate the 
certificate and the e-mail address.  Users are not very good at associating 
the correct certificate with the correct address book entry (that is, the 
correct e-mail address).  This mismatch has impacts on both authentication 
and confidentiality.

Russ