Modular Arithmetic

Modular arithmetic - Wikipedia

Congruence

Congruence modulo (article) | Cryptography | Khan Academy
$A\equiv B(\mathrm{mod}C)$

1. $\equiv$ is the symbol for congruence, which means the values A and B are in the same equivalence class.
2. (mod C) tells us what operation we applied to A and B.
3. when we have both of these, we call $\equiv$ congruence modulo C.

We say that r is congruent to s modulo n, or r is congruent to s mod n, if r − s is evenly divisible by n;

From Set

Set Theory

Modular Power

Complexity: $O(log(y))$ for $x^y$
Use Divide and Conquer Algorithm, $x^y=(x^{\lfloor y/2\rfloor }{)}^2$, like fast multiply algorithm.