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RE: The subject line leakage problem

2001-12-27 06:07:16

        I for one would be all in favor of putting in place a
fully spec'd kosher solution here. 

        However the issue of introduction and backwards compatibility
need to be carefully considered. We don't want to have people not
implement the full fix because they are waiting for others to deploy.

        I would like to keep the hack on the table as an interim
patch for the time being. Certainly the sooner we stop leaking
subject lines the better

        I don't consider the security of any other headers to be 
particularly serious. Routing info is disclosed as a matter of course 
and the existence of mailling lists and byzantine forwarding makes
the intended recipient issue impossible to resolve.


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

-----Original Message-----
From: Housley, Russ [mailto:rhousley(_at_)rsasecurity(_dot_)com]
Sent: Tuesday, December 18, 2001 9:42 AM
To: Hallam-Baker, Phillip
Cc: ietf-smime(_at_)imc(_dot_)org
Subject: Re: The subject line leakage problem


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 put
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 body
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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