RE: secure sign & encrypt

["Dominikus Scherkl" <[e-mail]>]

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
[e-mail]