encrypt: c = m^3 (mod 101)
decrypt: m = c^d (mod 101)
how would i solve for d (with the most efficient method by hand)?
So d is such that
Euler's theorem :
Here, n=101 and is prime.
3d has to be congruent to , i.e.
So we want to find the inverse of 3 modulo 100.
But you have to be careful, because either I've confused myself, either this is a particular case. In general, the number which would be at the same place as 101 is rarely prime.