Re: secure sign & encrypt

[Derek Atkins <warlord@xxxxxxx>]

The interesting thing is that there is nothing STOPPING an application
from doing this today.  OpenPGP messages like the following are
perfectly legal syntax, even in 2440:

ESK [...] Enc { PreSig ESK [...] Enc { Literal { Message } } PostSig }

Go ahead and implement this.  I'm fairly sure that most of the OpenPGP
Parsers out there will Do The Right Thing with this (I'm 99% sure that
PGP 6.5.x will do this, since I wrote that original parser code).

-derek

"Dominikus Scherkl" <Dominikus.Scherkl@xxxxxxxxxxxxxxx> writes:

> Hi.
> 
> > Well, I intended it to become an atomic function.
> Nice. And how? Common public key cryptography doesn't provide
> algorithms to sign an encrypt in a single, undividable step.
> 
> I see no other way than "encrypt, sign and encrypt" (ESE)
> to archive all cyptografic goals which seems inportant to me:
> 
> Two goals require ES:
> - to ensure that the reciever cannot forward a message
>   without destroying the signature or reveiling that it was
>   originaly send to him for his eyes only we must sign after
>   encryption.
> - to convince the receiver he was the original target we 
>   also need to first encryt and than sign.
> 
> two further goals require SE:
> - to ensure the signature is not used for another message
>   we must first sign than encrypt (else especialy for RSA
>   there exist a choosen key attack).
> - to hide that you are sending signed messages you also need
>   to do encryption as the very last step.
> 
> The easiest way to archive all four is ESE, an it is worth
> the time cost of two encryptions, I think.
> 
> Best Regards.
> 
> -- 
> Dominikus Scherkl
> dominikus.scherkl@xxxxxxxxxxxxxxx

-- 
       Derek Atkins, SB '93 MIT EE, SM '95 MIT Media Laboratory
       Member, MIT Student Information Processing Board  (SIPB)
       URL: http://web.mit.edu/warlord/    PP-ASEL-IA     N1NWH
       warlord@xxxxxxx                        PGP key available