From: Thomas DuBuisson <thomas.dubuisson@gmail.com>

>>class (Binary p, Serialize p) => AsymCipher p where
>>    generateKeypair :: RandomGen g => g -> BitLength -> Maybe ((p,p),g)
>>    encryptAsym     :: p -> B.ByteString -> B.ByteString
>>    decryptAsym     :: p -> B.ByteString -> B.ByteString
>>    asymKeyLength       :: p -> BitLength
>
> Regarding AsymCipher:
> Some algorithms do not lend themselves to encryption/decryption or have
> special properties which differentiate their use in enc/dec an
> signing/verifying.
>
> I propose the following two additions for the class:
> signAsym     :: p -> B.ByteString -> B.ByteString
> verifyAsym     :: p -> B.ByteString -> Bool
>
> This way algorithms can leave parts undefined which do not apply to
> them or hide their different behaviour.

I am strongly against classes for which we already know instanes will
need a good deal of undefined routines.