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Expression for Galois Fiels(2^8) multiplication:-

Which of the following expression is the correct one? please suggest.

Exp[ ( Log A + Log B )Mod 255]
[Exp( Log A + Log B )] Mod 255
Posted 8-Feb-12 21:25pm
Edited 14-Feb-12 20:07pm
SAKryukov 9-Feb-12 2:30am
What, no language tagged, nothing? This is off-topic. Do you need to learn mathematics? Learn it. Matrices is a really simple topics (but of course you will need a lot more). This is a wrong forum.
Ratika Agarwal 9-Feb-12 2:40am
I think you should do a bit homework on the questions posted in forums. B'coz you may be the only one who is not able to understand some term of it. If you know the ans.then post it. Else, let others help the needy ones.
SAKryukov 9-Feb-12 2:49am
Please do me a favor to decide by myself if I decide to post or not. Please don't take my words as an accusation in poor knowledge in mathematics or something like that. I just don't know it from your question. And to help you, I need to know what exactly you are missing. In this case, do you know the algorithm or not? Is there anything related to computer science or programming you need help with? I still don't understand it. Are you talking about matrix multiplication or something else?
Ratika Agarwal 9-Feb-12 2:33am
I don't need a language specific answer. I just want its logic and idea. It is a part of advance Mathematics, that's why I have tagged is as mathematics too.
SAKryukov 9-Feb-12 2:43am
Advanced..? He-he... :-)
Ratika Agarwal 9-Feb-12 2:47am
Quote me... "You are here to ask for help or to help somebody. Not to make fun of what you don't know about."
SAKryukov 9-Feb-12 2:50am
May I ask you why? :-)
You are talking as if this is something bad... :-)
SAKryukov 9-Feb-12 3:09am
Please, don't post non-solution as a solution. No one will see it anyway unless she or he loads this page, so it could not help you. And you are not answering my questions. Not to many people are dealing with this branch of mathematics anyway, so don't get hysterical. So far, your are the one who gets the most opportunities to find out the solution, but you still expect some help...
Ratika Agarwal 9-Feb-12 3:13am
What is your ques?? tell me.
SAKryukov 9-Feb-12 3:19am

1 solution

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Solution 1

Ratika Agarwal 9-Feb-12 2:35am
I know matrix operations very well. But my problem is to multiply in GALOIS FIELD(2 power n).
SAKryukov 9-Feb-12 2:41am
Good for you. I apologize then. But what tells you that Galois field requires matrix multiplication which is different. I think matrix multiplication is matrix multiplication. Please explain to me if I'm wrong.

And what's your problem? Is it programming or mathematics?
Ratika Agarwal 9-Feb-12 2:49am
A simple matrix not same as in Galois Field(2 power n). That is what I am asking here for, how to do it..
SAKryukov 9-Feb-12 2:55am
Sound surprising... do you know just the definition of the operation you need? I don't... "How" goes next...
SAKryukov 9-Feb-12 3:12am
Is it Vandermonde matrix multiplication over finite field?
Ratika Agarwal 9-Feb-12 3:22am
Yes. It is the multiplication over a Galois finite Field, but not over vandermonde.
SAKryukov 9-Feb-12 3:38am
I understand what's "over a finite field" but not "over Vandermonde" :-)
SAKryukov 9-Feb-12 3:40am
OK, where is the definition of a particular operation over a finite field and why you need that operation and not another?
Ratika Agarwal 9-Feb-12 3:45am
I need this particular operation for "Mix rows /columns operation of AES/Whirlpool algorithms" of cryptography.
SAKryukov 9-Feb-12 3:53am
There are a lot of open-source implementations of this algorithm...
SAKryukov 9-Feb-12 3:58am
This algorithm is more or less explained here, but I'm afraid, may be not in all detail:

Ratika Agarwal 9-Feb-12 3:30am
Thanks for help. But I have already searched a lot before coming to code project. I too came across this PDF, but it's not helpful.
SAKryukov 9-Feb-12 3:37am
Yes, that was my guess...
Espen Harlinn 9-Feb-12 8:44am
5'ed! - quite an effort :)
SAKryukov 9-Feb-12 12:21pm
Not at all, but thank you.

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