[3360] in cryptography@c2.net mail archive
Re: r.e. quality of IDEA...
daemon@ATHENA.MIT.EDU (Eric Young)
Thu Sep 24 13:51:44 1998
Date: Thu, 24 Sep 1998 15:50:06 +1000 (EST)
From: Eric Young <eay@cryptsoft.com>
To: John Kelsey <kelsey@plnet.net>
cc: Rodney Thayer <rodney@tillerman.nu>, cryptography@c2.net,
David Honig <honig@sprynet.com>
In-Reply-To: <199809240418.XAA04232@email.plnet.net>
On Wed, 23 Sep 1998, John Kelsey wrote:
> > The NSA asked the NIST to request that AES ciphers
> > be able to encrypt 2 blocks with 2 keys in the same
> > time as 2 blocks with 1 key. Ie, ciphers you can search
> > rapidly are mucho desirable from the perspective
> > of the eye in the sky.
>
> With the key sizes involved in the AES candidates, speeding up the
> rekeying
I made a post back in march which had some number for cipher I've implemted as
to the cost in cbc bytes for the key setup for my particular implementaions of
some ciphers.
It has some relvence and it is interesting to see that DES, without
modification is actually very good for the key_setup overhead.
eric
---
From eay@cryptsoft.com Wed Mar 11 23:03:57 1998
On Wed, 11 Mar 1998, Svend Olaf Mikkelsen wrote:
> On Tue, 10 Mar 1998 21:48:06 -0800, Alex Alten <Andrade@ix.netcom.com>
> wrote:
> >Interesting. A while back I looked at the DES key setup costs. Roughly 80%
> >of the time was spent in key setup as I changed the key for each small payload
> >(about 100 bytes).
> For DES, key setup time can be traded for memory. My guess would be
> that key setup using 32K tables can be as fast as an encryption.
I'll give numbers for my library, I've compiled everything using gcc under
linux, pentium pro 200. The key setup is always in C, the cipher speed is for
encrypting 8 bytes in cbc mode. These numbers are only approximate, but they
give a good approximation.
set_key C asm cost
DES 4.830uS 2.658uS 1.709uS 14.5 bytes
3-DES 14.490uS 7.141uS 4.827uS 16.2 bytes
IDEA 1.507uS enc 2.930uS 4.1 bytes
72.787uS dec 198.7 bytes
RC2 16.532uS 4.451uS 29.7 bytes
RC4 18.467uS 0.521uS 0.355uS 283.5 bytes
RC5-32-12 10.610uS 1.580uS 0.585uS 53.7 bytes
Blowfish 997.606uS 2.116uS 1.042uS 3771.6 bytes
CAST5 5.575uS 2.476uS 1.124uS 18.0 bytes
'cost' is the number of bytes that could have been crypted during a key setup.
So as you can see, a blowfish key setup takes the same amount of time as
encrypting 3.7k bytes. DES is actually very good for key setup cost. IDEA is
fast for encryption, but decryption is rather ugly. A half way value (100
bytes is probably a reasonable value if there is a bi-directional channel.
(I've compaired C set_key code to C code cbc mode encryption).
...crud deleted....
