Multiplicate a point on a elliptic curve

ECmultiplication.py

# a,b define a elliptic curve. y**2 = a*x**3 + b*x   
# G(x1,y1) is the base point.
# P is a large prime. N is the order of the base point and usually equals to the order of the curve.

def ECMultiplication(G,a,b,P,N,privateKey):
    #if privateKey < 1 or privateKey >= N: raise Exception("ECMultiplication(G,a,b,P,privateKey), privateKey should >0 and <N.")
    n_binary = str(bin(privateKey))[2:]
    D = G
    for i in range (1, len(n_binary)):
        D = ECdouble(D,a,b,P)
        if n_binary[i] == "1":
            D = ECadd(D, G)
    return D