Losing the Code War by Stephen Budiansky

[Joshua Hill]

marius wrote:
> Not quite true. Encrypting each message twice would not increase the
> "effective" key size to 112 bits.
> There is an attack named "meet in the middle" which will make the
> effective key size to be just 63 bits.

Peter Trei wrote:
> Don't forget that the MITM attack (which Schneier claims
> takes 2^(2n) = 2^112 time), also requires 2^56 blocks
> of storage.
[...]
> I don't lose sleep over MITM attacks on 3DES.

Unless I'm mistaken, the 2^63 operation MITM attack referenced in the
original message referred to Double-DES, not Triple-DES.  The original
cited value of 2^63 is incorrect; the Double-DES MITM attack (as proposed
by Merkle and Hellman) is a known plaintext attack that takes 2^57
operations, with 2^56 blocks of storage.

Your provided values are correct for attacking Triple-DES, but I don't
think that's what the original author was referring to.

				Josh

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