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Re: The subject line leakage problem

2001-12-18 08:14:00


Thanks for raising this issue.

After the intended-recipients discussion, it was clear to me that several 
RFC 821 header lines needed various forms of protection.  The level of 
automated checking is different for each of them.  Some need 
confidentiality, and others do not (and cannot without disrupting the mail 

I would like to steer this discussion toward a signed attribute (a CHOICE 
of IA5String and UTF8String (for international characters that are coming 
soon)).  The attribute would contain a subset of the header lines.

My initial cut at the header lines that ought to be included are FROM, TO, 
CC, SUBJECT, and DATE.  So, for Phil's message that started this thread, 
the attribute would contain:

     From: "Hallam-Baker, Phillip" <pbaker(_at_)verisign(_dot_)com>
     Cc: ietf-smime(_at_)imc(_dot_)org
     Subject: The subject line leakage problem
     Date: Mon, 17 Dec 2001 10:34:39 -0800

I think that the content-hints attribute defined in RFC 2634 should be used 
to carry the real subject line when the RFC 821 header carries a masked 
subject line.


At 10:34 AM 12/17/2001 -0800, Hallam-Baker, Phillip wrote:

        One of the ongoing problems with people using PGP is that people
confidential information in the mail subject lines, eg:

Subject: Proposed purchase of Excite(_at_)Home
Subject: Your STD test results
Subject: Planned head count reduction


So over the years there have been plenty of fixes involving CMS encrypted
attributes etc. which gets into the rat hole of what other headers to add

So instead of that how about the following fix:

1) A Best Current Practice Draft that says
2) Clients SHOULD offer users the option of replacing the subject line on
confidential messages and carrying the subject as the first line in the
of the message.

So the above message would become

Subject: Confidential
Subject: Confidential
Subject: Confidential

And when opened we get something like:

Subject: Confidential

Subject: Proposed purchase of Excite(_at_)Home

        Yadda Yadda Yadda ....

        So, no need for any modification of existing specs, complete
backwards interop and the bug in the spec gets fixed.


Phillip Hallam-Baker FBCS C.Eng.
Principal Scientist
VeriSign Inc.
781 245 6996 x227

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