I'm currently trying to figure out how the Baby Step Giant Step algorithm works and there's a step which I don't really understand. (You can see it here: http://en.wikipedia.org/wiki/Baby_step_giant_step)
Basically, its step 3. where you calculate alpha^-m.
So my question is, how do you calculate the modulus of e.g. 2^-10 mod 101? I think I need the answer to be an integer in order for this algorithm to work.
Thanks a lot!
Best Answer
You calculate it as $(2^{-1})^{10}$. You calculate the inverse of $2 \pmod{101}$ by the extended euclidean algorithm, in this case it is 51, because $51 * 2 = 102 = 1 \pmod{101}$. Then you raise 51 to the power of 10 (by fast exponentiation), of course,$\mod{101}$.