Re: RSA decryption exponent d (c++)

TJakobsen wrote:
> hehe sorry but i dont really understand how to use this in my program
> as im only a high school student (last year though). We don't have
> advanced mathematics yet and we haven't really worked with any of the
> mathematics related to RSA such as modulo etc.
>
> could someone be so kind as to go through this Extended Euclidian
> algorithn using the numbers i've used in my program please?
> so we can calculate d.

   Perhaps you can translate this Java into your C++.

long inverse(long ee, long mm) {
   if (ee<=1) {
     if (ee==1) {
       return 1;
     }
     throw new IllegalArgumentException(
      "ee must be >=1, not "+ee);
   }
   // If we can find ss and tt such that
   // ss*ee+tt*mm=1
   // then ss would be the inverse of ee modulo mm. We
   // could return ss=(1-tt*mm)/ee or, even better,
   // (1-tt*mm)/ee+mm, which is >=1.

   // When we take the equation ss*ee+tt*mm=1 modulo
   // ee, it becomes
   // tt*mm==1 mod ee,
   // so one value that would work for tt is the inverse
   // of mm modulo ee.
   return (1-inverse(mm%ee, ee)*mm)/ee+mm;
}

--Mike Amling
Received on Mon May 1 01:54:16 2006