Stefan Claas wrote: > Helmut Waitzmann Anti-Spam-Ticket.b.qc3c wrote: > > > Stefan Claas <s...@300baud.de>: > > > > >I was reading old GnuPG threads were people were asking if it's > > >possible to extract a signature from an encrypted message. > > > > > >I would like to ask, I don't know if this is already possible or > > >if it's planned, if Alice would request from Bob that he always > > >signs his messages and Bob, lazy as he is, often forgets this, > > >can Alice check if Bob's encrypted message(s) have signed byte(s) > > >set, without actually decrypting or revealing Bob's identity? > > > > As far as I know this is impossible, because messages are first > > signed and then encrypted, i. e. the signature is encrypted, > > too. Therefore there is no access to the signature unless the > > message is decrypted. > > > > >If the encrypted messages would not be signed then Alice can > > >simply discard the message(s). > > > > Yes, but why should she want to be able to do that? She could > > decrypt the message and, if it turns out that the message is not > > signed, discard the message. > > It would allow Alice (in her organization), or others, to do a > pre-check, with procmail etc., to set-up an auto-responder, informing > Bob that he did not signed his message and that his message will be > discarded. > > > >And is this optional in GnuPG, in case it is already implemented? > > > > > > As far as I know the order “first sign, then encrypt” is > > mandatory, so there is no way for GnuPG to deviate from it. > > > > And this is a good thing, as it thwarts Eve eavesdropping on the > > originator's identity (i. e. Bob) of a message sent to Alice. > > It should be not a mandatory feature and it should only append > secured bytes, which are stating that Bob's message contains a > signature (yes|no bytes), without revealing his identity. > Assuming the would technically possible.
I think something along the lines like Zero Knowledge Proof Encryption. Regards Stefan -- NaClbox: cc5c5f846c661343745772156a7751a5eb34d3e83d84b7d6884e507e105fd675 The computer helps us to solve problems, we did not have without him. _______________________________________________ Gnupg-users mailing list Gnupg-users@gnupg.org http://lists.gnupg.org/mailman/listinfo/gnupg-users
