> From: [email protected] [mailto:discuss-
> [email protected]] On Behalf Of Kent Borg
> 
> Bruteforcing
> 128-bits is impossible.  Bruteforcing 256-bits is 128-bits times as
> impossible.

Careful here.  Someday, there might exist a perfect block cipher, but at 
present, all known block ciphers (including AES) suffer from the even-vs-odd 
permutation problem, which means, that a cipher with 128 bit key is only as 
strong as an ideal cipher with 64 bits.  If you want 128 bit strength (BigO 
2^128 operations to brute force attack), you have to use the 256 bit key.

I don't have a reference I can point you to on the internet.  I read this in 
Cryptography Engineering (Schneier, Ferguson, Kohno).
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