前端传来一个SM2加密后的密码，后端用SM2私钥解密，java

实现如下：

1.首先，需要引入BouncyCastle库，这是一个密码学库，用于支持SM2算法。

import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.engines.SM2Engine;
import org.bouncycastle.crypto.params.ECPrivateKeyParameters;
import org.bouncycastle.crypto.params.ParametersWithRandom;
import org.bouncycastle.crypto.util.PrivateKeyFactory;
import org.bouncycastle.crypto.util.PublicKeyFactory;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.util.encoders.Base64;
import java.security.Security;

2.使用BouncyCastleProvider提供者进行初始化。

Security.addProvider(new BouncyCastleProvider());

3.获取SM2私钥和加密的密码。

String privateKeyStr = "私钥字符串";
String encryptedPassword = "加密后的密码字符串";

4.将私钥转化为ECPrivateKeyParameters类型。

byte[] privateKeyBytes = Base64.decode(privateKeyStr);
ECPrivateKeyParameters privateKey = (ECPrivateKeyParameters) PrivateKeyFactory.createKey(privateKeyBytes);

5.将加密的密码转化为byte数组。

byte[] encryptedPasswordBytes = Base64.decode(encryptedPassword);

6.使用SM2算法进行解密。

SM2Engine engine = new SM2Engine();
CipherParameters param = new ParametersWithRandom(privateKey);
engine.init(false, param);
byte[] decryptedPasswordBytes = engine.processBlock(encryptedPasswordBytes, 0, encryptedPasswordBytes.length);

7.将解密后的密码转化为字符串。

String decryptedPassword = new String(decryptedPasswordBytes);

完整代码实现：

import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.engines.SM2Engine;
import org.bouncycastle.crypto.params.ECPrivateKeyParameters;
import org.bouncycastle.crypto.params.ParametersWithRandom;
import org.bouncycastle.crypto.util.PrivateKeyFactory;
import org.bouncycastle.crypto.util.PublicKeyFactory;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.util.encoders.Base64;
import java.security.Security;

public class SM2Util {
    public static void main(String[] args) {
        Security.addProvider(new BouncyCastleProvider());
        String privateKeyStr = "私钥字符串";
        String encryptedPassword = "加密后的密码字符串";
        try {
            byte[] privateKeyBytes = Base64.decode(privateKeyStr);
            ECPrivateKeyParameters privateKey = (ECPrivateKeyParameters) PrivateKeyFactory.createKey(privateKeyBytes);
            byte[] encryptedPasswordBytes = Base64.decode(encryptedPassword);
            SM2Engine engine = new SM2Engine();
            CipherParameters param = new ParametersWithRandom(privateKey);
            engine.init(false, param);
            byte[] decryptedPasswordBytes = engine.processBlock(encryptedPasswordBytes, 0, encryptedPasswordBytes.length);
            String decryptedPassword = new String(decryptedPasswordBytes);
            System.out.println(decryptedPassword);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}