在Java中使用double和add方法实现点乘法

Question

I'm trying to implement the double and add method of scalar multiplication of ECDSA based on the pseudo code below:

Algorithm 1 (Double-and-add) 

    input P

    Q ← P

    for i from l−2 to 0 do

        Q ← 2Q

        if i = 1 then Q ← Q + P 

    output Q

And here is my java code:

public static ECPoint ScalarMulti(BigInteger ks, ECPoint G) {
    String k = ks.toString(2);
    ECPoint q = new ECPoint(zero, zero);
    q = G;
    for (int i = k.length() - 2; i >= 0; i--) {
        q = DoublePoint(q);
        if (k.substring(i, i + 1).equals("1")) {
            q = Pointaddition(q, G);
        }
    }
    return q;
}

}

But the signature verification is always failed (I am sure there are no mistakes in other codes), what is the problem here? Is the pseudo code correct? If it is, what's wrong with my code?

Answer 1

Due to the lack of code you provided it is the best java code possible to implement your algorithm. Your code was containing logical errors.

public static ECPoint ScalarMulti(BigInteger ks) {
    ECPoint p = new ECPoint(zero, zero);
    ECPoint q = p;
    for (BigInteger i = obj.subtract(new BigInteger("2")); //initialization
            i.compareTo(new BigInteger("0")) >= 0;  // comparision
            i = i.subtract(new BigInteger("1"))) {  // increment
        q = DoublePoint(q);
        if (i.compareTo(new BigInteger("1")) {
            q = Pointaddition(p, q);
        }
    }
    return q;
}