Re: A weakness in PGP signatures, and a suggested solution (long)

17 Dec 2003

      -----BEGIN PGP SIGNED MESSAGE-----

Hello ckey2@eng.ua.edu (Christopher R. Key)
  and cypherpunks@toad.com
...
In article <Pine.ULT.3.91.960110182255.18692H-100000@xdm011>, Jeffrey Goldberg <cc047@Cranfield.ac.uk> says:
...
First of all, if the recipient is a newsgroup, why would that particular
information need to be part of the signed information?  If you post to a
...
Somebody already pointed out an adult message being re-posted to a kidgroup.

...
...
Secondly, if you are sending email to some one and sign it using pgp, wouldn't
that person need pgp to prove that in fact you did sign it?  Then it can be
...
So if all that needs be done to a message to insure that the appropriate 
person reads it is encrypt it using their public key, why does pgp (or one
of the pgp interfaces) need to be changed to include header information?  
...
But then the recipient has a PGP-signed message from you which
isn't encrypted (using pgp -d). That person could then impersonate
you. Eg Alice the jilted lover could resend the goodbye message
with forged headers to Bob's new girlfriend to get back at him.

What a sentence. Here it is again, hopefully understandable:

Bob->Alice
  From:Bob; Encrypted(Signed("We're through",Bob),Alice)

Alice does pgp -d, leaving her with Signed("We're through",Bob)

Alice->Carol
  From:Bob; Encrypted(Signed("We're through",Bob),Carol)

Later, when Bob gets another girlfriend,

Alice->Danielle
  From:Bob; Encrypted(Signed("We're through",Bob),Danielle)

Later still,

Alice->Eve
  From:Bob; Encrypted(Signed("We're through",Bob),Eve)

Re: A weakness in PGP signatures, and a suggested solution (long)

Jiri Baum