Square roots of big numbers

With application to zero knowledge proofs

I wrote two posts today about square roots of big numbers.

The first was about testing whether a number n has a square root modulo a large prime p. Doing this for a set of large consecutive numbers has been proposed as a part of a zero knowledge proof of custody in Etherium 2.0. See Legendre and Ethereum.

The other post revisits an algorithm I wrote about many years ago for determining whether an integer is a perfect square. The new post explores the algorithm’s faults and presents a better algorithm. It includes simple Python code that works for arbitrarily large integers.

Enjoy.