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s0m3l0s3r
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Post subject: exptmod Posted: 10 May 2010 02:56 |
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Joined: 10 May 2010 02:25 Posts: 2
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Not sure if anyone here can help, but I was directed here by a friend.
Using a large number library, I'm using a function called mp_exptmod (Currently using LibTomMath) What this does is a calculation such as, (a ** b) % c = d
I'm attempting to try a reversal of this somehow, and have no idea where to start (math isn't really my strong point lol) I have two samples, (3989164954469923270136 ** 7922973163614769257511) % 12090425874644131058489 = 19749455703201550423 (1343852261239897004666 ** 7922973163614769257511) % 12090425874644131058489 = 22838020368551383127
And one I'm trying to reverse: (??? ** 7922973163614769257511) % 12090425874644131058489 = 19155424029236793431
Can anyone here give me any idea as to an efficient method to generate a list of values that the first value could be to get that answer? There's a maximum value of 37778931862957161709567 that I know of. And trying 0 - 37778931862957161709567 would be unrealistic to calculate...
Thanks in advance for any suggestions/ideas.
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aluigi
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Post subject: Re: exptmod Posted: 10 May 2010 08:54 |
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Joined: 13 Aug 2007 21:44 Posts: 4068 Location: http://aluigi.org
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I guess that the "**" operator should be the power instruction, anyway the problem is the "%" one because divisions and (moreover) modulus cut parts of the original number that so can't be recovered.
it's like having "100%3=1" and trying to recover 100 from the other 2 known numbers... impossible.
math is not my best field (ih ih ih) anyway I bet on the "impossible direct reversing" option.
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s0m3l0s3r
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Post subject: Re: exptmod Posted: 13 May 2010 05:38 |
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Joined: 10 May 2010 02:25 Posts: 2
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Thanks for the response.
I understand how the math works, I just have no idea on reverse operations.
In "100%3=1", the 100 really isn't that important to me. I'd be fine with 1, 4, 7, anything. I don't need the exact, I'm just looking for anything that gives the expected result. If you have any ideas, I'd love to hear them.
Thanks again for your time, I know this seems pretty useless, but it's mostly curiosity that won't let me ignore it lol
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aluigi
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Post subject: Re: exptmod Posted: 13 May 2010 10:52 |
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Joined: 13 Aug 2007 21:44 Posts: 4068 Location: http://aluigi.org
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in this case the operation you must do is the radix but yeah it's totally useless here because it will return ever a 0 due to the truncation of the original result with modulus: result = 19155424029236793431 radix 7922973163614769257511
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