# Fiat-Shamir zero knowledge protocol

In Fiat-Shamir protocol, the final calculation is

$$y^2=x\,v^c$$

Where $$c$$ is the random $$\{1,0\}$$, $$x$$ is the witness and $$v$$ is the public key $$s^2 \bmod n$$.

My questions are:

1. What stops the attacker from reading $$c$$, which is never encrypted, $$v$$ which is public and then calculate $$y^2$$ correctly?
2. How does this improve entity authentication?