[Mailman-Users] Preserving S/MIME-Encoded Mail

[Grant Taylor]

On 01/16/09 15:46, Barry Finkel wrote:
> Note that Mailman has taken the existing three-part MIME structure 
> (plain-text body, HTML-formatted body, and digital signature) and 
> instead of placing the list footer as a fourth part in the same MIME 
> structure, Mailman has created a new two-part MIME structure with 
> the original three-part MIME structure as a first part and the list 
> footer as a second part.  While this resulting structure is valid 
> MIME-encoding (I think), the result is that the initial header lines

<snip>

> are not at the beginning of the MIME structure.  I believe that this 
> is causing the mail to appear as an unsigned mail message.  I have just 
> begun reading "S/MIME 3.1" RFC 3851, and my initial quick reading 
> leads me to believe that this
> 
>      Content-Type: multipart/signed;
> 
> header line needs to appear in the first part of the MIME headers 
> and not within a subsidiary MIME header.

If I recall correctly, S/MIME signed messages are exactly that, signed 
/messages/ as in the entirety of the email (short of some headers).  As 
such, any form of altering the message will break the S/MIME signature.

> Is there a reason why Mailman does not place the list footer as a 
> fourth section in the existing MIME structure?  Thanks.

I think the more proper thing would be for something (Mailman or it's 
MTA interface / handler) to validate S/MIME signed messages and process 
them before passing them on.  I think that if a message has been signed 
and it has been altered in transport, the fact that it failed 
authentication should either be noted or the entire message should be 
rejected out right.  Which ever your preference is, I think this issue 
is really a larger mailing list manager conceptual issue than just 
something that Mailman is or is not doing.

I think a similar mentality applies to S/MIME encrypted (as opposed to 
signed) messages too.



Grant. . . .