SM2Util.createPoint 怎么实现

SM2Util.createPoint是一个用于创建SM2椭圆曲线点的静态方法。以下是一个简单的实现：

import org.bouncycastle.math.ec.ECCurve;
import org.bouncycastle.math.ec.ECPoint;
import org.bouncycastle.math.ec.FixedPointCombMultiplier;

import java.math.BigInteger;

public class SM2Util {
    private static final ECCurve curve = new ECCurve.Fp(
            new BigInteger("FFFFFFFEFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF00000000FFFFFFFFFFFFFFFC", 16),
            new BigInteger("FFFFFFFEFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF00000000FFFFFFFFFFFFFFFC", 16),
            new BigInteger("FFFFFFFEFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF00000000FFFFFFFFFFFFFFFC", 16));
    private static final ECPoint G = curve.createPoint(
            new BigInteger("04", 16),
            new BigInteger("79BE667EF9DCBBAC55A06295CE870B07029BFCDB2DCE28D959F2815B16F81798", 16),
            new BigInteger("483ADA7726A3C4655DA4FBFC0E1108A8FD17B448A68554199C47D08FFB10D4B8", 16));

    public static ECPoint createPoint(String xHex, String yHex) {
        BigInteger x = new BigInteger(xHex, 16);
        BigInteger y = new BigInteger(yHex, 16);
        return curve.createPoint(x, y);
    }

    public static ECPoint getG() {
        return G;
    }

    public static ECPoint multiply(ECPoint point, BigInteger factor) {
        FixedPointCombMultiplier multiplier = new FixedPointCombMultiplier();
        return multiplier.multiply(point, factor);
    }
}

这个实现使用了bouncycastle库提供的ECCurve和ECPoint类来创建椭圆曲线点。它还提供了一个getG方法来获取SM2算法中预定义的基点G。multiply方法可以使用SM2算法中的倍点运算来计算点的倍数。在这个例子中，我们使用了FixedPointCombMultiplier来执行倍点运算，它是bouncycastle库提供的一种高效的倍点运算实现。