Oops, pressed "send" too soon.

On Sat 11 Jan 2014 at 18:26:28 +0100, Rhialto wrote:
> As you can see at 
> http://en.wikipedia.org/wiki/Block_cipher_mode_of_operation#Output_feedback_.28OFB.29
> when decrypting in OFB mode, a corruption in one cyphertext block does
> *not* propagate to any next block! In effect, the block cypher is merely
> used to generate a stream of pseudo-random bits which are 

XORed with the plain text to generate the ciphertext.

Which means that an attacker can trivially flip any bits in the file
that (s)he wishes.

-Olaf.
-- 
___ Olaf 'Rhialto' Seibert  -- The Doctor: No, 'eureka' is Greek for
\X/ rhialto/at/xs4all.nl    -- 'this bath is too hot.'

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