java实现sm4

SM4是一种国密算法，Java中可以使用Bouncy Castle库来实现。

首先需要引入Bouncy Castle库，可以在Maven中添加以下依赖：

<dependency>
    <groupId>org.bouncycastle</groupId>
    <artifactId>bcpkix-jdk15on</artifactId>
    <version>1.66</version>
</dependency>

然后就可以使用以下代码实现SM4加解密：

import org.bouncycastle.crypto.BlockCipher;
import org.bouncycastle.crypto.CipherParameters;
import org.bouncycastle.crypto.engines.SM4Engine;
import org.bouncycastle.crypto.params.KeyParameter;
import org.bouncycastle.crypto.params.ParametersWithIV;
import org.bouncycastle.util.encoders.Hex;

import java.nio.charset.StandardCharsets;
import java.security.SecureRandom;

public class SM4Util {
    private static final int BLOCK_SIZE = 16;

    /**
     * 加密
     */
    public static byte[] encrypt(byte[] key, byte[] iv, byte[] data) {
        SM4Engine engine = new SM4Engine();
        BlockCipher cipher = new CBCBlockCipher(engine);
        CipherParameters params = new ParametersWithIV(new KeyParameter(key), iv);
        cipher.init(true, params);

        int inputLen = data.length;
        int paddingLen = BLOCK_SIZE - (inputLen % BLOCK_SIZE);
        byte[] input = new byte[inputLen + paddingLen];
        System.arraycopy(data, 0, input, 0, inputLen);
        for (int i = 0; i < paddingLen; i++) {
            input[inputLen + i] = (byte) paddingLen;
        }

        byte[] output = new byte[input.length];
        int i = 0;
        while (i < input.length) {
            int len = cipher.processBlock(input, i, output, i);
            i += len;
        }

        return output;
    }

    /**
     * 解密
     */
    public static byte[] decrypt(byte[] key, byte[] iv, byte[] data) {
        SM4Engine engine = new SM4Engine();
        BlockCipher cipher = new CBCBlockCipher(engine);
        CipherParameters params = new ParametersWithIV(new KeyParameter(key), iv);
        cipher.init(false, params);

        byte[] output = new byte[data.length];
        int i = 0;
        while (i < data.length) {
            int len = cipher.processBlock(data, i, output, i);
            i += len;
        }

        int paddingLen = output[output.length - 1];
        byte[] result = new byte[output.length - paddingLen];
        System.arraycopy(output, 0, result, 0, result.length);

        return result;
    }

    public static void main(String[] args) {
        byte[] key = Hex.decode("0123456789abcdeffedcba9876543210");
        byte[] iv = new byte[BLOCK_SIZE];
        new SecureRandom().nextBytes(iv);

        String plaintext = "Hello, world!";
        byte[] ciphertext = encrypt(key, iv, plaintext.getBytes(StandardCharsets.UTF_8));
        System.out.println("Ciphertext: " + Hex.toHexString(ciphertext));

        byte[] decrypted = decrypt(key, iv, ciphertext);
        String decryptedText = new String(decrypted, StandardCharsets.UTF_8);
        System.out.println("Decrypted text: " + decryptedText);
    }
}

其中，加密和解密都需要传入密钥和IV，IV需要随机生成，加密时还需要进行PKCS7填充。