Banks and 128 bit DES

[Ben Laurie]

Jeffrey Goldberg wrote:
> 
> 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.

Depends which flavour of 3DES. IIRC the variant used in SSL has 3
different keys giving an effective strength of 112 (+ a few) bits.

> > 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).

Right, they are, but neither is considered sufficiently mature to use in
SSL.

Cheers,

Ben.

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