Bug#170069: ITP: grunt -- Secure remote execution via UUCP or e-mail using GPG

[Brian May <bam@debian.org>]

On Fri, Nov 22, 2002 at 09:47:48AM -0600, John Goerzen wrote:
> On Fri, Nov 22, 2002 at 12:24:34AM -0500, Joey Hess wrote:
> > > After verifying the signature on the data, the receiver does some sanity
> > > checks.  One of the checks is doing an md5sum over the entire file
>                                                   ^^^^^^^^^^^^^^^^^^^^
> > > (remember, this includes both the headers and the payload).  If it
> > > has seen the same md5sum in the last 60 days, it rejects the request.  If
> > > the date of the request was more than 30 days ago, it rejects the request.
> > 
> > Hold on, if you're md5summing the headers, what is to stop an attacker
> > from modifying the subject, and using an intercepted, gpg-signed body to
> > repeat the command?
> 
> It's an md5sum over the entire file.  The file includes both the headers and
> the body.

No, I think the question might be "what if the MD5SUM is different but
the GPG signature is the same"?

I think it depends on the method used to sign the message, some methods
sign the headers, some don't.

So if I manually sign a message, and include it in the body of this
message, it won't protect the headers in anyway.

Somebody could alter the headers, resulting in the md5sum becomming
altered, and the message won't be detected as a replay.

Also, to prevent another possible (maybe obvious) attack; make sure your
clock is set correctly (and not some time in the future) before sending
a email...
--
Brian May <bam@debian.org>