使用Java代码实现一个国密算法

国密算法是中国自主开发的密码算法，包括SM1、SM2、SM3和SM4等。其中，SM2是非对称加密算法，SM3是哈希算法，SM4是对称加密算法。这里我们以SM2为例，使用Java代码实现SM2算法。

首先，需要使用Bouncy Castle库来实现SM2算法。可以在Maven中添加以下依赖：

<dependency>
    <groupId>org.bouncycastle</groupId>
    <artifactId>bcpkix-jdk15on</artifactId>
    <version>1.68</version>
</dependency>

然后就可以使用以下代码实现SM2算法：

import org.bouncycastle.crypto.AsymmetricCipherKeyPair;
import org.bouncycastle.crypto.digests.SM3Digest;
import org.bouncycastle.crypto.engines.SM2Engine;
import org.bouncycastle.crypto.generators.ECKeyPairGenerator;
import org.bouncycastle.crypto.params.ECDomainParameters;
import org.bouncycastle.crypto.params.ECKeyGenerationParameters;
import org.bouncycastle.crypto.params.ECPrivateKeyParameters;
import org.bouncycastle.crypto.params.ECPublicKeyParameters;
import org.bouncycastle.crypto.signers.SM2Signer;
import org.bouncycastle.jce.provider.BouncyCastleProvider;
import org.bouncycastle.jce.spec.ECPrivateKeySpec;
import org.bouncycastle.jce.spec.ECPublicKeySpec;

import java.math.BigInteger;
import java.security.KeyFactory;
import java.security.KeyPair;
import java.security.Security;
import java.security.spec.ECGenParameterSpec;
import java.security.spec.ECParameterSpec;
import java.security.spec.ECPoint;

public class SM2Utils {

    private static final String SM2_CURVE_NAME = "sm2p256v1"; // SM2的椭圆曲线参数
    private static final int SM2_DIGEST_SIZE = 32; // SM3哈希函数输出长度为32字节

    static {
        Security.addProvider(new BouncyCastleProvider());
    }

    /**
     * 生成SM2密钥对
     * @return SM2密钥对
     * @throws Exception 异常
     */
    public static KeyPair generateKeyPair() throws Exception {
        ECGenParameterSpec ecGenParameterSpec = new ECGenParameterSpec(SM2_CURVE_NAME);
        ECKeyPairGenerator ecKeyPairGenerator = new ECKeyPairGenerator();
        ecKeyPairGenerator.init(new ECKeyGenerationParameters(new ECDomainParameters(ecGenParameterSpec.getCurve(), ecGenParameterSpec.getG(), ecGenParameterSpec.getN()), null));
        AsymmetricCipherKeyPair keyPair = ecKeyPairGenerator.generateKeyPair();
        ECPrivateKeyParameters privateKey = (ECPrivateKeyParameters) keyPair.getPrivate();
        ECPublicKeyParameters publicKey = (ECPublicKeyParameters) keyPair.getPublic();
        KeyFactory keyFactory = KeyFactory.getInstance("EC", "BC");
        ECParameterSpec ecParameterSpec = new ECParameterSpec(ecGenParameterSpec.getCurve(), ecGenParameterSpec.getG(), ecGenParameterSpec.getN());
        ECPrivateKeySpec privateKeySpec = new ECPrivateKeySpec(privateKey.getD(), ecParameterSpec);
        ECPublicKeySpec publicKeySpec = new ECPublicKeySpec(new ECPoint(publicKey.getQ().getAffineXCoord().toBigInteger(), publicKey.getQ().getAffineYCoord().toBigInteger()), ecParameterSpec);
        return new KeyPair(keyFactory.generatePublic(publicKeySpec), keyFactory.generatePrivate(privateKeySpec));
    }

    /**
     * SM2签名
     * @param data 待签名数据
     * @param privateKey 私钥
     * @return 签名结果
     * @throws Exception 异常
     */
    public static byte[] sign(byte[] data, BigInteger privateKey) throws Exception {
        ECGenParameterSpec ecGenParameterSpec = new ECGenParameterSpec(SM2_CURVE_NAME);
        SM2Signer signer = new SM2Signer();
        signer.init(true, new ECPrivateKeyParameters(privateKey, new ECDomainParameters(ecGenParameterSpec.getCurve(), ecGenParameterSpec.getG(), ecGenParameterSpec.getN())));
        signer.update(data, 0, data.length);
        return signer.generateSignature();
    }

    /**
     * SM2验签
     * @param data 待验签数据
     * @param publicKey 公钥
     * @param signature 签名结果
     * @return 验签结果
     * @throws Exception 异常
     */
    public static boolean verify(byte[] data, byte[] publicKey, byte[] signature) throws Exception {
        ECGenParameterSpec ecGenParameterSpec = new ECGenParameterSpec(SM2_CURVE_NAME);
        SM2Signer signer = new SM2Signer();
        signer.init(false, new ECPublicKeyParameters(new ECPoint(new BigInteger(1, publicKey), new BigInteger(1, publicKey, 32)), new ECDomainParameters(ecGenParameterSpec.getCurve(), ecGenParameterSpec.getG(), ecGenParameterSpec.getN())));
        signer.update(data, 0, data.length);
        return signer.verifySignature(signature);
    }

    /**
     * SM3哈希
     * @param data 待哈希数据
     * @return 哈希结果
     * @throws Exception 异常
     */
    public static byte[] hash(byte[] data) throws Exception {
        SM3Digest digest = new SM3Digest();
        digest.update(data, 0, data.length);
        byte[] hash = new byte[SM2_DIGEST_SIZE];
        digest.doFinal(hash, 0);
        return hash;
    }

    /**
     * SM2加密
     * @param data 待加密数据
     * @param publicKey 公钥
     * @return 加密结果
     * @throws Exception 异常
     */
    public static byte[] encrypt(byte[] data, byte[] publicKey) throws Exception {
        ECGenParameterSpec ecGenParameterSpec = new ECGenParameterSpec(SM2_CURVE_NAME);
        SM2Engine engine = new SM2Engine();
        engine.init(true, new ECPublicKeyParameters(new ECPoint(new BigInteger(1, publicKey), new BigInteger(1, publicKey, 32)), new ECDomainParameters(ecGenParameterSpec.getCurve(), ecGenParameterSpec.getG(), ecGenParameterSpec.getN())));
        return engine.processBlock(data, 0, data.length);
    }

    /**
     * SM2解密
     * @param data 待解密数据
     * @param privateKey 私钥
     * @return 解密结果
     * @throws Exception 异常
     */
    public static byte[] decrypt(byte[] data, BigInteger privateKey) throws Exception {
        ECGenParameterSpec ecGenParameterSpec = new ECGenParameterSpec(SM2_CURVE_NAME);
        SM2Engine engine = new SM2Engine();
        engine.init(false, new ECPrivateKeyParameters(privateKey, new ECDomainParameters(ecGenParameterSpec.getCurve(), ecGenParameterSpec.getG(), ecGenParameterSpec.getN())));
        return engine.processBlock(data, 0, data.length);
    }

}

使用示例：

KeyPair keyPair = SM2Utils.generateKeyPair();
byte[] publicKey = ((ECPublicKey) keyPair.getPublic()).getEncoded();
byte[] privateKey = ((ECPrivateKey) keyPair.getPrivate()).getEncoded();
byte[] data = "hello world".getBytes();

// 签名
byte[] signature = SM2Utils.sign(SM2Utils.hash(data), new BigInteger(1, privateKey));
System.out.println("signature: " + Hex.encodeHexString(signature));

// 验签
boolean verifyResult = SM2Utils.verify(SM2Utils.hash(data), publicKey, signature);
System.out.println("verifyResult: " + verifyResult);

// 加密
byte[] encryptedData = SM2Utils.encrypt(data, publicKey);
System.out.println("encryptedData: " + Hex.encodeHexString(encryptedData));

// 解密
byte[] decryptedData = SM2Utils.decrypt(encryptedData, new BigInteger(1, privateKey));
System.out.println("decryptedData: " + new String(decryptedData));

需要注意的是，SM2算法使用的椭圆曲线参数为sm2p256v1，哈希函数为SM3，输出长度为32字节。在使用时需要注意参数的设置。