public BigInteger SquareRootModPrime(BigInteger a, BigInteger p)
{
long e = 0, r, s;
BigInteger b = 0, bp = 0, q = p - 1, m = 0, n = 0;
BigInteger p1 = p - 1, t = 0, x = 0, y = 0, z = 0;
m = q % 2;
while (m == 0)
{
q = q / 2;
m = q % 2;
e++;
}
int jac = 0;
do
{
n = RandomRange(1, p1);
jac = Maths.JacobiRand(n, p);
}while (jac == -1);
z = BigInteger.ModPow(n, q, p);
y = z;
r = e;
x = BigInteger.ModPow(a, (q - 1) / 2, p);
b = (((a * x) % p) * x) % p;
x = (a * x) % p;
while (true)
{
if (b == 1 || b == p1)
{
return(x);
}
s = 1;
do
{
bp = BigInteger.ModPow(b, (long)Math.Pow(2, s), p);
s++;
}while (bp != 1 && bp != p1 && s < r);
if (s == r)
{
return(0);
}
t = BigInteger.ModPow(y, (long)Math.Pow(2, r - s - 1), p);
y = (t * t) % p;
x = (x * t) % p;
b = (b * y) % p;
r = s;
}
}
