[Mailman-Users] mailman, attachment and digital sign
Marco De Rossi
Marco.DeRossi at roma1.infn.it
Thu Aug 30 16:47:53 CEST 2007
If it could be helpful: it seems happen only sending e-mail from a Windows
XP operating system (sending e-mail from a linux OS the digital signature
Thanks, Marco De Rossi
On Thu, 30 Aug 2007, Marco De Rossi wrote:
> I tried to turn off all "Content Filtering" but it didn't fixed the
> signature problem.
> Some other suggestion?
> Thanks, Marco De Rossi
> On Thu, 2 Aug 2007, Brad Knowles wrote:
> > On 8/2/07, Marco De Rossi wrote:
> > > We have modifed mailman so now it not add the message footer anymore.
> > > Now we still have this problem only when we send digital signed e-mail
> > > *with attachment*.
> > I can see two likely possibilities:
> > 1. The digital signature is being done against the whole message,
> > headers included. When the message passes through Mailman, some
> > headers end up getting changed or added, and the signature is no
> > longer valid.
> > 2. Mailman is still stripping or changing some of the attachment
> > MIME types or filenames, which causes the signature to be invalidated.
> > Problem is, cryptographic signatures on messages are extremely
> > fragile. If even the slightest thing is changed, the signature is
> > likely to be broken. If you make the signature process more robust,
> > then you increase the possibility that an attacker could slip
> > something through that would still appear to be correct, but where
> > they've actually secretly modified something.
> > Try turning off all filtering, HTML conversion, etc... within
> > Mailman. See if that "fixes" the signature problem. If so, then you
> > have to decide which is more important -- the signature on some
> > messages or the probability that some malware could get through the
> > system and sent out to all recipients of the list, because you'd
> > turned off the filtering.
> > Unfortunately, this is a binary decision. There is no option to
> > leave signed messages unfiltered and to apply the filtering rules
> > only to unsigned messages. Even if there were such a method, the
> > attackers could get through by simply forging fake signatures that
> > look valid.
> > --
> > Brad Knowles <brad at shub-internet.org>, Consultant & Author
> > LinkedIn Profile: <http://tinyurl.com/y8kpxu>
> > Slides from Invited Talks: <http://tinyurl.com/tj6q4>
> > 09 F9 11 02 9D 74 E3 5B D8 41 56 C5 63 56 88 C0
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