Given an elliptic curve $y^2 = x^3 + ax + b$ over a finite field $\mathbf{F}_p$, how can I retrieve the value of $y$ given the value of $x$?
My knowledge in this area is quite limited, so I understand this question might seems silly.
I'm currently working on an application that uses an elliptic curves library and I saw at some point that this value was retrieved via: $$(x^3 + ax + b)^{(p+1) >> 2} \mod p$$
the $>>$ means shift right though I am not sure what this means mathematically.
Does this make sense?
Thanks.