[8273] in cryptography@c2.net mail archive
Re: IBM press release - encryption and authentication
daemon@ATHENA.MIT.EDU (Nikita Borisov)
Tue Dec 12 01:25:55 2000
Message-Id: <200012120603.WAA16075@croissant.isaac.cs.berkeley.edu>
In-Reply-To: Your message of "Tue, 12 Dec 2000 13:54:42 +1100."
<4.3.1.0.20001212134110.00b8ed28@127.0.0.1>
To: Greg Rose <ggr@qualcomm.com>
Cc: cryptography@c2.net
Date: Mon, 11 Dec 2000 22:03:57 -0800
From: Nikita Borisov <nikitab@CS.Berkeley.EDU>
Greg Rose writes:
>At 05:14 PM 12/11/2000 -0800, Nikita Borisov wrote:
>>But in his examples, addition mod 2^128 - 159 can be implemented rather
>>quickly:
>>
>>S_i = S_{i-1} + b [regular 128-bit addition]
>>if (b > S_i) S_i += 159
>
>Ahhh, yes, a classical example of premature optimisation. This is, of
>course, a different definition of modular arithmetic than most people would
>use.
Well, it _does_ find a number congruent to S_{i-1} + b mod (2^128-159),
which is one definition of modular addition. But you're right -- unless
both sides are using this version of the algorithm, a final reduction is
necessary to find a representation in the range [0,2^128-159). I should
have looked at his slides more carefully...
- Nikita
