java sm4

Java SM4是一种对称加密算法，它使用固定长度（128位）的密钥对数据进行加密和解密。Java SM4算法的实现可以使用Bouncy Castle等Java密码库来进行。

以下是使用Bouncy Castle实现Java SM4加密和解密的示例代码：

import org.bouncycastle.crypto.engines.SM4Engine;
import org.bouncycastle.crypto.modes.CBCBlockCipher;
import org.bouncycastle.crypto.paddings.PKCS7Padding;
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.Security;

public class SM4Example {
    public static void main(String[] args) throws Exception {
        // 加载Bouncy Castle库
        Security.addProvider(new org.bouncycastle.jce.provider.BouncyCastleProvider());

        // 待加密的明文
        String plaintext = "Hello world!";
        byte[] plainBytes = plaintext.getBytes(StandardCharsets.UTF_8);

        // 128位密钥
        String keyHex = "0123456789abcdeffedcba9876543210";
        byte[] keyBytes = Hex.decode(keyHex);

        // 128位初始向量
        String ivHex = "0123456789abcdef0123456789abcdef";
        byte[] ivBytes = Hex.decode(ivHex);

        // 加密
        CBCBlockCipher cipher = new CBCBlockCipher(new SM4Engine());
        PKCS7Padding padding = new PKCS7Padding();
        cipher.init(true, new ParametersWithIV(new KeyParameter(keyBytes), ivBytes));
        byte[] ciphertext = new byte[cipher.getOutputSize(plainBytes.length)];
        int len = cipher.processBytes(plainBytes, 0, plainBytes.length, ciphertext, 0);
        len += cipher.doFinal(ciphertext, len);
        System.out.println("Ciphertext: " + Hex.toHexString(ciphertext));

        // 解密
        cipher.init(false, new ParametersWithIV(new KeyParameter(keyBytes), ivBytes));
        byte[] decrypted = new byte[cipher.getOutputSize(len)];
        int decryptedLen = cipher.processBytes(ciphertext, 0, len, decrypted, 0);
        decryptedLen += cipher.doFinal(decrypted, decryptedLen);
        String decryptedText = new String(decrypted, 0, decryptedLen, StandardCharsets.UTF_8);
        System.out.println("Decrypted text: " + decryptedText);
    }
}

在这个示例中，我们使用Bouncy Castle库来实现Java SM4算法的加密和解密，并使用16字节（128位）的密钥和初始向量。加密过程使用CBC模式和PKCS7填充方式。