Banks and 128 bit DES

[Jeffrey Goldberg]

On Mon, 20 Mar 2000, Ben Laurie wrote:

> Hmm. Although 3DES uses 168 bits, it has an effective strength of 112
> bits.

Does it really use 168 bits.  I thought it used key-1 (56) bits for the
first encipherment, key-2 (the second 56 bits) for the second, and then
back to key-1 again for the third.  Using a separate key for the third
would only make it effectively 113 bits for attacking.

> The 128 bit limit is simply due to their being no available
> symmetric ciphers that are stronger.

I thought RC5 and Blowfish at least are parameterizable to >128 bit keys.

Am I mistaken?  Is this the wrong place to ask this?  (I suspect an answer
of "yes" to both).

-j

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