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Subject: Re: q&d comparison (was Re: [Cryptix-Users] Rijndael - thereal work now begins)
From: Ben Laurie (benalgroup.co.uk)
Date: Sun Oct 08 2000 - 15:28:03 CDT

Bill Stewart wrote:
>
> Does "90% faster" than DES mean "Rijndael takes 10% as long
> as DES" or "DES takes 190% as long as Rijndael"?
>
> Also, since DES isn't strong enough, comparing Rijndael speed
> to 3DES is more appropriate - which says Rijndael has a significant
> speed advantage.
>
> Ben Laurie commented on 3DES really only having 112 bits of strength -
> but for this question, which is how much entropy you need for your keys,
> 168 bits is the right answer.

Apologies - I only saw the snipped version, which didn't make it clear
what the question was.

Even so, there are triple-DESes which use only 112 bits of key.

Cheers,

Ben.

>
> At 12:32 PM 10/8/00 -0400, Ian Grigg wrote:
> >Fred Baube wrote:
> >> Would someone like to make a quick 'n dirty comparison among
> >> DES, 3DES, and Rijndael in terms of key entropy required and
> >> processing time required ? Give us all some quantifiable
> >> motivation to switch ASAP ...
> >
> >There is plenty of stuff on the NIST site, but you'd have to dig
> >for it. There are lots of comparisons in the NSA report.
> >
> >Some early results say that Rijndael is about 40% (256) and 90%
> >(128) faster than DES in encryption (decryption is slightly
> >slower than those speedups).
> >
> >Key set up is about 5 times faster than DES (encryption) and
> >3 times faster than DES (decryption) with some drop off (4, 2.5)
> >for 256 bit keys.
> >
> >On the amount of entropy, well, I'd leave that to a cryptographer,
> >other than the observation that Rijndael has 128, 192, 256 bit keys,
> >whilst DES has 56 bits and T-DES has 168 (full).
>
> Thanks!
> Bill
> Bill Stewart, bill.stewartpobox.com
> PGP Fingerprint D454 E202 CBC8 40BF 3C85 B884 0ABE 4639 

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