WARNING: signature digest conflict in message ?

[Brian Candler]

On Thu, Sep 25, 2008 at 08:17:25PM +0100, Brian Candler wrote:
>     clearsigned message <-------> message + detached signature

Actually that particular one should be pretty simple: I think a clearsigned
message is just an armored detached signature stuck onto the end of the
message. A simple perl or ruby script could split them, although you'll need
to be careful to munge line endings properly.

Also, I thought of another solution. RFC 2440 says:

   If more than one message digest is used in the signature, the "Hash"
   armor header contains a comma-delimited list of used message digests.

So perhaps if you add a fake header

  Hash: MD5,SHA1

to those messages which don't have a "Hash:" header, then it will verify
correctly. I did a quick experiment, clearsigning a message and changing

  Hash: SHA1

to

  Hash: MD5,SHA1

and the signature still verified. So you just need to check that a MD5+RSA
message still verifies with this header, and you're away.

HTH,

Brian.