When using power_mod(a,b,c) we get a^b % c returning x. I have a,c, and x but am having a difficult time reversing the %c.
Is there a function that already exists to reverse this, or would I need to implement Euclidean algorithm to find what b is and return that?
This sounds like the "discrete logarithm" problem. If not, please be clearer (e.g., give a specific numeric example). But, if so, as the cited article says, there is no efficient approach known for the general case.
Since you tagged "sage" in the question, see the docs for the Sage discrete_log() function too. It implements some of the approaches named in the earlier cited Wikipedia article ("Pohlig-Hellman and baby step giant step").
