Re: IBM press release - encryption and authentication

[David Wagner]

Enzo Michelangeli wrote:
>OpenPGP tries to detect such "wrong key" situations for
>symmetrically-encrypted packets in a pretty simplistic way, [...]
>   The repetition of 16 bits in the 80 bits of random data prefixed to
>   the message allows the receiver to immediately check whether the
>   session key is incorrect.

This does not provide message integrity or message authentication.
It provides a much weaker property: If you've decrypted with the wrong
key, this will let you detect that fact.

For message integrity or authentication, it seems that you need either
a full-blown MAC or else some scheme like Charanjit Jutla's.