SM2只有私钥情况下解密

结合了两个大佬的代码，目前应该都是第一个大佬的代码

第一个Android_国密_SM2、SM3、SM4_ylineyline的专栏-优快云博客

第二个Android常用加密库集合_lambert_Lei的专栏-优快云博客

首先导入包：Android_国密_SM2、SM3、SM4_ylineyline的专栏-优快云博客

implementation 'org.bouncycastle:bcprov-jdk16:1.46'

接下来，都是自定义的东西不要找SM2的包在哪，SM2是自己的类

package com.iqilu.phonetoken.utils;

import android.text.TextUtils;
import org.bouncycastle.crypto.generators.ECKeyPairGenerator;
import org.bouncycastle.crypto.params.ECDomainParameters;
import org.bouncycastle.crypto.params.ECKeyGenerationParameters;
import org.bouncycastle.math.ec.ECCurve;
import org.bouncycastle.math.ec.ECFieldElement;
import org.bouncycastle.math.ec.ECFieldElement.Fp;
import org.bouncycastle.math.ec.ECPoint;

import java.math.BigInteger;
import java.security.SecureRandom;


public class SM2 {

    // 正式参数
    public static final String[] ecc_param = {
            "FFFFFFFEFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF00000000FFFFFFFFFFFFFFFF",
            "FFFFFFFEFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF00000000FFFFFFFFFFFFFFFC",
            "28E9FA9E9D9F5E344D5A9E4BCF6509A7F39789F515AB8F92DDBCBD414D940E93",
            "FFFFFFFEFFFFFFFFFFFFFFFFFFFFFFFF7203DF6B21C6052B53BBF40939D54123",
            "32C4AE2C1F1981195F9904466A39C9948FE30BBFF2660BE1715A4589334C74C7",
            "BC3736A2F4F6779C59BDCEE36B692153D0A9877CC62A474002DF32E52139F0A0"
    };

    public final BigInteger ecc_p;
    public final BigInteger ecc_a;
    public final BigInteger ecc_b;
    public final BigInteger ecc_n;
    public final BigInteger ecc_gx;
    public final BigInteger ecc_gy;

    public final ECCurve ecc_curve;
    public final ECPoint ecc_point_g;

    public final ECDomainParameters ecc_bc_spec;
    public final ECKeyPairGenerator ecc_key_pair_generator;

    public final ECFieldElement ecc_gx_fieldelement;
    public final ECFieldElement ecc_gy_fieldelement;

    public SM2() {
        this.ecc_p = new BigInteger(ecc_param[0], 16);
        this.ecc_a = new BigInteger(ecc_param[1], 16);
        this.ecc_b = new BigInteger(ecc_param[2], 16);
        this.ecc_n = new BigInteger(ecc_param[3], 16);
        this.ecc_gx = new BigInteger(ecc_param[4], 16);
        this.ecc_gy = new BigInteger(ecc_param[5], 16);

        this.ecc_gx_fieldelement = new Fp(this.ecc_p, this.ecc_gx);
        this.ecc_gy_fieldelement = new Fp(this.ecc_p, this.ecc_gy);

        this.ecc_curve = new ECCurve.Fp(this.ecc_p, this.ecc_a, this.ecc_b);
        this.ecc_point_g = new ECPoint.Fp(this.ecc_curve, this.ecc_gx_fieldelement, this.ecc_gy_fieldelement);

        this.ecc_bc_spec = new ECDomainParameters(this.ecc_curve, this.ecc_point_g, this.ecc_n);

        this.ecc_key_pair_generator = new ECKeyPairGenerator();
        this.ecc_key_pair_generator.init(new ECKeyGenerationParameters(this.ecc_bc_spec, new SecureRandom()));
    }
    

    /**
     * 解密
     * @param value 需要解密数据(默认传入为16进制数据)
     * @param key 密钥（需要16进制字符串，其他编码请使用byte[]）
     * @return
     */
    public String simpleDeCode(String value, String key) {
        if(TextUtils.isEmpty(value)|| TextUtils.isEmpty(key)){
            return null;
        }
        byte[] datas=Utils.hexStringToBytes(value);
        byte[] keyBytes=Utils.hexStringToBytes(key);
        return new String(deCode(datas,keyBytes));
    }

    public byte[] deCode(byte[] value, byte[] key) {
        if (value==null||key==null)
        {
            return null;
        }
        //加密字节数组转换为十六进制的字符串 长度变为value.length * 2
        String data = Utils.byteToHex(value);
        /***分解加密字串
         * （C1 = C1标志位2位 + C1实体部分128位 = 130）
         * （C2 = encryptedData.length * 2 - C1长度  - C2长度）
         * （C3 = C3实体部分64位  = 64）
         */
        byte[] c1Bytes = Utils.hexToByte(data.substring(0,130));
        int c2Len = value.length - 97;
        byte[] c2 = Utils.hexToByte(data.substring(130,130 + 2 * c2Len));
        byte[] c3 = Utils.hexToByte(data.substring(130 + 2 * c2Len,194 + 2 * c2Len));

        BigInteger userD = new BigInteger(1, key);

        //通过C1实体字节来生成ECPoint
        ECPoint c1 =ecc_curve.decodePoint(c1Bytes);
        Cipher cipher = new Cipher();
        cipher.Init_dec(userD, c1);
        cipher.Decrypt(c2);
        cipher.Dofinal(c3);
        //返回解密结果
        return c2;
    }


}

简单就是直接解密

参考第二篇文章直接用就行

M2 sm2 = new SM2();
String s = sm2.simpleDeCode(message, getPrivate_secret());