RE: Twofish/AES News (bogus performance claims?)

Dutra de Lacerda (dulac@ip.pt)
Thu, 10 Dec 1998 21:19:33 +0000

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The 'C' implementation runs slower on the AMD because the compiler
optimizes for Intel (Intels hand here).

I assume that a hand optimized ASM implementation for AMD K6 will
run faster than a similar P-II implementation. The reason? Simply
because the K6 is more efficient in Operations/Clock ... specially
working with integers where the lack of the L2 is not relevant.

At Thursday, you wrote:
>I agree that Brian's code gets very impressive results for C. I ran my
>assembler and (slower) C benchmarks on many machines, using the Pentium
>timer to get high resolution timing, so I'm quite confident that the
>assembler numbers are real. I know almost nothing about AMD or Cyrix CPU
>optimizations, so unfortunately I have no idea why it runs so much slower.
>
>Thanks for the time and interest in Twofish.
>
>-----Original Message-----
>From: Alex Alten
>To: Doug Whiting
>Cc: 'CodherPlunks@toad.com'; 'schneier@counterpane.com'
>Sent: 12/10/98 9:06 AM
>Subject: RE: Twofish/AES News (bogus performance claims?)
>
>Doug,
>
>Well I tried out Brian's code. I timed it at about 7.5 MBytes/sec
>which is close enough to the 8 MB/sec I interpolated from your paper.
>I'm impressed with Brian's C code. To get within 70-80% of the assembly
>speeds is a fine piece of work. Usually C at best is 50% the speed of
>assembly. Given this result I'll believe that your assembly timings
>are accurate. Interestingly my K6 200 here at home runs at only 4 MB/s
>for both versions.
>
>- Alex
>
>At 02:55 PM 12/4/98 -0800, Doug Whiting wrote:
>>Sorry for the confusion, Alex. The C performance numbers we used were
>the
>>'best' taken from the AES submissions themselves and any other place we
>>could find them. In particular, the 400 clocks/block number came from
>Brian
>>Gladman's C version, which he wrote to optimize for the Pentium Pro.
>The C
>>code we submitted to NIST did not run that fast; we spent our time
>>optimizing the assembly version. You can see Brian's tables and get
>his
>>code from:
>>
>>http://www.seven77.demon.co.uk/aes.htm
>>
>>I hope this clarifies things.
>>
>>-----Original Message-----
>>From: Alex Alten
>>To: Doug Whiting
>>Sent: 12/4/98 9:48 AM
>>Subject: Re: Twofish/AES News (bogus performance claims?)
>>
>>At 03:24 PM 12/3/98 -0600, Bruce Schneier wrote:
>>>There are some new papers on the Twofish webpage.
>>>
>>>We have improved our performance numbers. On Pentium-class machines,
>>key
>>
>>I noticed you are claiming an encrypt of 400 cycles/block on a Pentium
>>Pro
>>200. This translates to 8 MB/sec enciphering speed. I tried your
>>optimized
>>C version and could only get 3 MB/sec (with a 128 bit key ECB mode). I
>>was
>>careful to ensure that the cipher worked with test data in a main
>memory
>>to
>>main memory encipherment. You are overstating TwoFish's real world
>>performance by a factor of about 2.5 . This makes me suspicious of
>your
>>
>>assembler version speed claims, maybe it really runs at 760 c/block?
>>
>>I used Microsoft MSVC 4.2. I set the optimizations for maximum speed
>and
>>to
>>emit Pentium Pro specific assembler code. I've included my test code
>>and a
>>slightly modified AES.h file, so that you can see for yourself how I
>>tested
>>it. I used your TWOFISH2.C AES submission code version 1.00, dated
>>April
>>1998.
>>
>>- Alex
>>
>>
>>--
>>
>>Alex Alten
>>
>>Alten@Home.Com
>>Alten@TriStrata.Com
>>
>>P.O. Box 11406
>>Pleasanton, CA 94588 USA
>>(925) 417-0159
>>
>> <<Aes.h>>
>>
>--
>
>Alex Alten
>
>Alten@Home.Com
>Alten@TriStrata.Com
>
>P.O. Box 11406
>Pleasanton, CA 94588 USA
>(925) 417-0159

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