[Cryptography Team] Re: SSL Error

[Chris Muller]

> Ok I found the problem.
> 
> CBC>>initialVector: aByteArray
> 	"Ferguson and Schneier recommend this on page 72 of 'Practical
> Cryptography'."
> 	cipher encryptBlock: aByteArray.
> 	super initialVector: aByteArray
> 
> Since encrypt and decrypt use initialVector this adds an additional
> encrypt
> into every pass.  Deleting this method fixes the problem.  I
> understand the
> intent here so we should either remove initialVector from encrypt and
> decrypt and set vector directly (adding the destroy method from the
> superclass initialVector method) or remove this method.
> 
> What do you think?

Oh, great catch Ron.  I had used the Refactory to abstract
BlockCipherMode>>'vector', I didn't noticed this result.

#initialVector: is somewhat of a misnomer for encrypting block to block
because it's supposed to be for the *initial* block.

So I posted a fix to Core that adds BlockCipherMode>>#vector:, which
simply sets the vector (still avoiding leakage), while #initialVector:
still encrypts the IV per Schneiers recommendation.

The CBC test had to be adjusted to account for this (i.e., we cannot
compare ciphertexts after a key-change).  You should also adjust your
Rfc tests to account for the same (i.e., it seems to be a more a test
of Rijndael, I would reset the #vector: to the unencrypted value in the
spec right after setting the initialVector:).

Thanks!
  Chris