版本：jdk1.8
Maven依赖：

<dependency>
    <groupId>cn.hutool</groupId>
    <artifactId>hutool-all</artifactId>
    <version>5.5.4</version>
</dependency>
<dependency>
    <groupId>org.bouncycastle</groupId>
    <artifactId>bcprov-jdk15to18</artifactId>
    <version>1.66</version>
</dependency>

版本：jdk1.7
Maven依赖：

<dependency>
    <groupId>cn.hutool</groupId>
    <artifactId>hutool-all</artifactId>
    <version>4.6.17</version>
</dependency>
<dependency>
    <groupId>org.bouncycastle</groupId>
    <artifactId>bcprov-jdk15to18</artifactId>
    <version>1.63</version>
</dependency>

代码示例：

import cn.hutool.core.util.CharsetUtil;
import cn.hutool.crypto.SmUtil;
import cn.hutool.crypto.symmetric.SymmetricCrypto;

import java.nio.charset.StandardCharsets;

public class Main {
    /**
     * 加密
     *
     * @param msg
     * @return
     */
    public static String encrypt(String key,String msg) {
        SymmetricCrypto sm4 = SmUtil.sm4(key.getBytes(StandardCharsets.UTF_8));
        //加密
        String encryptHex = sm4.encryptHex(msg);
        return encryptHex;
    }

    /**
     * 解密
     * @param key
     * @param msg
     * @return
     */
    public static String dencrypt(String key,String msg){
        SymmetricCrypto sm4 = SmUtil.sm4(key.getBytes(StandardCharsets.UTF_8));
        //解密
        String decryptStr = sm4.decryptStr(msg, CharsetUtil.CHARSET_UTF_8);
        return decryptStr;
    }

    public static void main(String[] args) {
        // key必须是16位
        String key="1234567890123456";
        String name = "fisco bcos";
        name = Main.encrypt(key,name);
        System.out.println(name);
        System.out.println(Main.dencrypt(key,name));
    }
}

控制台输出：

sm4加密，解密java工具类

最近项目中和第三方接口对接，客户方需要采用sm4加密，故上网研究了下，但是没有找到好用的工具类，所以我整理了一份，供参考，亲测有效。
前提：需要添加maven 依赖

        <dependency>
        <groupId>org.bouncycastle</groupId>
        <artifactId>bcprov-jdk15on</artifactId>
        <version>1.66</version>
        </dependency>
    
    <dependency>
        <groupId>cn.hutool</groupId>
        <artifactId>hutool-all</artifactId>
        <version>5.4.1</version>
    </dependency>

代码：

public class Sm4Util {
static {
    Security.addProvider(new BouncyCastleProvider());
}

private static final String ENCODING = "UTF-8";
public static final String ALGORITHM_NAME = "SM4";

//加密算法/分组加密模式/分组填充方式
//PKCS5Padding-以8个字节为一组分组加密
//定义分组加密模式使用：PKCS5Padding

public static final String ALGORITHM_NAME_ECB_PADDING = "SM4/ECB/PKCS5Padding";

//128-32位16进制;256-64位16进制

public static final int DEFAULT_KEY_SIZE = 128;

/**
 * 生成ECB暗号
 *
 * @param algorithmName 算法名称
 * @param mode          模式
 * @param key
 * @return
 * @throws Exception
 * @explain ECB模式（电子密码本模式：Electronic codebook）
 */
private static Cipher generateEcbCipher(String algorithmName, int mode, byte[] key) throws Exception {
    Cipher cipher = Cipher.getInstance(algorithmName, BouncyCastleProvider.PROVIDER_NAME);
    Key sm4Key = new SecretKeySpec(key, ALGORITHM_NAME);
    cipher.init(mode, sm4Key);
    return cipher;
}

public static byte[] generateKey() throws Exception {
    return generateKey(DEFAULT_KEY_SIZE);
}

public static byte[] generateKey(int keySize) throws Exception {
    KeyGenerator kg = KeyGenerator.getInstance(ALGORITHM_NAME, BouncyCastleProvider.PROVIDER_NAME);
    kg.init(keySize, new SecureRandom());
    return kg.generateKey().getEncoded();
}

/**
 * sm4加密
 *
 * @param hexKey   16进制秘钥（忽略大小写）
 * @param paramStr 待加密字符串
 * @return 返回16进制的加密字符串
 * @throws Exception
 */
public static String encryptEcb(String hexKey, String paramStr) throws Exception {
    String cipherText = "";
    // 16进制字符串-->byte[]
    byte[] keyData = ByteUtils.fromHexString(hexKey);
    // String-->byte[]
    byte[] srcData = paramStr.getBytes(ENCODING);
    // 加密后的数组
    byte[] cipherArray = encrypt_Ecb_Padding(keyData, srcData);
    // byte[]-->hexString
    cipherText = ByteUtils.toHexString(cipherArray);
    return cipherText;
}

/**
 * 加密模式之Ecb
 *
 * @param key
 * @param data
 * @return
 * @throws Exception
 * @explain
 */
public static byte[] encrypt_Ecb_Padding(byte[] key, byte[] data) throws Exception {
    Cipher cipher = generateEcbCipher(ALGORITHM_NAME_ECB_PADDING, Cipher.ENCRYPT_MODE, key);
    return cipher.doFinal(data);
}

/**
 * sm4解密
 *
 * @param hexKey     16进制密钥
 * @param cipherText 16进制的加密字符串（忽略大小写）
 * @return 解密后的字符串
 * @throws Exception
 * @explain 解密模式：采用ECB
 */
public static String decryptEcb(String hexKey, String cipherText) throws Exception {
    // 用于接收解密后的字符串
    String decryptStr = "";
    // hexString-->byte[]
    byte[] keyData = ByteUtils.fromHexString(hexKey);
    // hexString-->byte[]
    byte[] cipherData = ByteUtils.fromHexString(cipherText);
    // 解密
    byte[] srcData = decrypt_Ecb_Padding(keyData, cipherData);
    // byte[]-->String
    decryptStr = new String(srcData, ENCODING);
    return decryptStr;
}

/**
 * @param key
 * @param cipherText
 * @return
 * @throws Exception
 */
public static byte[] decrypt_Ecb_Padding(byte[] key, byte[] cipherText) throws Exception {

    Cipher cipher = generateEcbCipher(ALGORITHM_NAME_ECB_PADDING, Cipher.DECRYPT_MODE, key);
    return cipher.doFinal(cipherText);
}

/**
 * 校验加密前后的字符串是否为同一数据
 *
 * @param hexKey     16进制密钥（忽略大小写）
 * @param cipherText 16进制加密后的字符串
 * @param paramStr   加密前的字符串
 * @return 是否为同一数据
 * @throws Exception
 * @explain
 */
public static boolean verifyEcb(String hexKey, String cipherText, String paramStr) throws Exception{
    // 用于接收校验结果
    boolean flag = false;
    // hexString-->byte[]
    byte[] keyData = ByteUtils.fromHexString(hexKey);
    // 将16进制字符串转换成数组
    byte[] cipherData = ByteUtils.fromHexString(cipherText);
    // 解密
    byte[] decryptData = decrypt_Ecb_Padding(keyData, cipherData);
    // 将原字符串转换成byte[]
    byte[] srcData = paramStr.getBytes(ENCODING);
    // 判断2个数组是否一致
    flag = Arrays.equals(decryptData, srcData);
    return flag;
}


public static void main(String[] args) throws Exception {
    String key = "86C63180C2806ED1F47B859DE501215B";
    String s = "QAZXSWEDCVFR";
    String jiami = Sm4Util.encryptEcb(key, s);
    System.out.println("加密====" + jiami);
    String jiemi = Sm4Util.decryptEcb(key, jiami);
    System.out.println("解密====" + jiemi);
    byte[] bs = ByteUtils.fromHexString(key);
    System.out.println(Arrays.toString(bs));
    System.out.println(ByteUtils.toHexString(generateKey()));

    String str = "86C63180C2806ED1F47B859DE501215B";
    int byte_len = str.getBytes("utf-8").length;
    int len = str.length();
    System.out.println("字节长度为：" + byte_len);
    System.out.println("字符长度为：" + len);
    System.out.println("系统默认编码方式：" + System.getProperty("file.encoding"));

}

/**
 * 国密SM4
 *
 * @author Luke-lee
 */
public class SM4Util {

    private static byte[] iv = {1, 2, 3, 4, 5, 6, 7, 8};
    private static final String CODE_UTF8 = "UTF-8";
    private static final String PASSWORD_CRYPT_KEY = "CSSssDes";
    private static final String KEY_ = "LUKE018YfzXjGB81";
    private static final int ROUND = 32;
    private static final int ENCRYPT = 1;
    private static final int DECRYPT = 0;
    private static final int BLOCK = 16;

    private byte[] Sbox = {(byte) 0xd6, (byte) 0x90, (byte) 0xe9, (byte) 0xfe, (byte) 0xcc, (byte) 0xe1, 0x3d,
            (byte) 0xb7, 0x16, (byte) 0xb6, 0x14, (byte) 0xc2, 0x28, (byte) 0xfb, 0x2c, 0x05, 0x2b, 0x67, (byte) 0x9a,
            0x76, 0x2a, (byte) 0xbe, 0x04, (byte) 0xc3, (byte) 0xaa, 0x44, 0x13, 0x26, 0x49, (byte) 0x86, 0x06,
            (byte) 0x99, (byte) 0x9c, 0x42, 0x50, (byte) 0xf4, (byte) 0x91, (byte) 0xef, (byte) 0x98, 0x7a, 0x33, 0x54,
            0x0b, 0x43, (byte) 0xed, (byte) 0xcf, (byte) 0xac, 0x62, (byte) 0xe4, (byte) 0xb3, 0x1c, (byte) 0xa9,
            (byte) 0xc9, 0x08, (byte) 0xe8, (byte) 0x95, (byte) 0x80, (byte) 0xdf, (byte) 0x94, (byte) 0xfa, 0x75,
            (byte) 0x8f, 0x3f, (byte) 0xa6, 0x47, 0x07, (byte) 0xa7, (byte) 0xfc, (byte) 0xf3, 0x73, 0x17, (byte) 0xba,
            (byte) 0x83, 0x59, 0x3c, 0x19, (byte) 0xe6, (byte) 0x85, 0x4f, (byte) 0xa8, 0x68, 0x6b, (byte) 0x81,
            (byte) 0xb2, 0x71, 0x64, (byte) 0xda, (byte) 0x8b, (byte) 0xf8, (byte) 0xeb, 0x0f, 0x4b, 0x70, 0x56,
            (byte) 0x9d, 0x35, 0x1e, 0x24, 0x0e, 0x5e, 0x63, 0x58, (byte) 0xd1, (byte) 0xa2, 0x25, 0x22, 0x7c, 0x3b,
            0x01, 0x21, 0x78, (byte) 0x87, (byte) 0xd4, 0x00, 0x46, 0x57, (byte) 0x9f, (byte) 0xd3, 0x27, 0x52, 0x4c,
            0x36, 0x02, (byte) 0xe7, (byte) 0xa0, (byte) 0xc4, (byte) 0xc8, (byte) 0x9e, (byte) 0xea, (byte) 0xbf,
            (byte) 0x8a, (byte) 0xd2, 0x40, (byte) 0xc7, 0x38, (byte) 0xb5, (byte) 0xa3, (byte) 0xf7, (byte) 0xf2,
            (byte) 0xce, (byte) 0xf9, 0x61, 0x15, (byte) 0xa1, (byte) 0xe0, (byte) 0xae, 0x5d, (byte) 0xa4, (byte) 0x9b,
            0x34, 0x1a, 0x55, (byte) 0xad, (byte) 0x93, 0x32, 0x30, (byte) 0xf5, (byte) 0x8c, (byte) 0xb1, (byte) 0xe3,
            0x1d, (byte) 0xf6, (byte) 0xe2, 0x2e, (byte) 0x82, 0x66, (byte) 0xca, 0x60, (byte) 0xc0, 0x29, 0x23,
            (byte) 0xab, 0x0d, 0x53, 0x4e, 0x6f, (byte) 0xd5, (byte) 0xdb, 0x37, 0x45, (byte) 0xde, (byte) 0xfd,
            (byte) 0x8e, 0x2f, 0x03, (byte) 0xff, 0x6a, 0x72, 0x6d, 0x6c, 0x5b, 0x51, (byte) 0x8d, 0x1b, (byte) 0xaf,
            (byte) 0x92, (byte) 0xbb, (byte) 0xdd, (byte) 0xbc, 0x7f, 0x11, (byte) 0xd9, 0x5c, 0x41, 0x1f, 0x10, 0x5a,
            (byte) 0xd8, 0x0a, (byte) 0xc1, 0x31, (byte) 0x88, (byte) 0xa5, (byte) 0xcd, 0x7b, (byte) 0xbd, 0x2d, 0x74,
            (byte) 0xd0, 0x12, (byte) 0xb8, (byte) 0xe5, (byte) 0xb4, (byte) 0xb0, (byte) 0x89, 0x69, (byte) 0x97, 0x4a,
            0x0c, (byte) 0x96, 0x77, 0x7e, 0x65, (byte) 0xb9, (byte) 0xf1, 0x09, (byte) 0xc5, 0x6e, (byte) 0xc6,
            (byte) 0x84, 0x18, (byte) 0xf0, 0x7d, (byte) 0xec, 0x3a, (byte) 0xdc, 0x4d, 0x20, 0x79, (byte) 0xee, 0x5f,
            0x3e, (byte) 0xd7, (byte) 0xcb, 0x39, 0x48};
    private int[] CK = {0x00070e15, 0x1c232a31, 0x383f464d, 0x545b6269, 0x70777e85, 0x8c939aa1, 0xa8afb6bd, 0xc4cbd2d9,
            0xe0e7eef5, 0xfc030a11, 0x181f262d, 0x343b4249, 0x50575e65, 0x6c737a81, 0x888f969d, 0xa4abb2b9, 0xc0c7ced5,
            0xdce3eaf1, 0xf8ff060d, 0x141b2229, 0x30373e45, 0x4c535a61, 0x686f767d, 0x848b9299, 0xa0a7aeb5, 0xbcc3cad1,
            0xd8dfe6ed, 0xf4fb0209, 0x10171e25, 0x2c333a41, 0x484f565d, 0x646b7279};

    public static String encodeSMS4(String plaintext) throws Exception {
        return SM4Util.encodeSMS4(plaintext, null);
    }

    public static String encodeSMS4(String plaintext, String key) throws Exception {
        if (!StringUtils.hasText(plaintext)) {
            return null;
        }
        byte[] b = encryptDES(plaintext).getBytes(CODE_UTF8);
        byte[] rstr = SM4Util.encodeSMS4(b, key);
        return ConvertUtil.byteToHex(rstr);
    }

    /**
     * 不限明文长度的SMS4加密
     *
     * @param plaintext
     * @param key
     * @return
     */
    private static byte[] encodeSMS4(byte[] plaintext, String key) {
        byte[] ciphertext = new byte[plaintext.length];
        int k = 0;
        int plainLen = plaintext.length;
        while (k + 16 <= plainLen) {
            byte[] cellPlain = new byte[16];
            System.arraycopy(plaintext, k, cellPlain, 0, 16);
            byte[] cellCipher = encode16(cellPlain, key);
            System.arraycopy(cellCipher, 0, ciphertext, k, cellCipher.length);
            k += 16;
        }
        return ciphertext;
    }

    /**
     * 不限明文长度的SMS4解密
     *
     * @param ciphertext
     * @param key
     * @return
     */
    private static byte[] decodeSMS4(byte[] ciphertext, String key) {
        byte[] plaintext = new byte[ciphertext.length];
        int k = 0;
        int cipherLen = ciphertext.length;
        while (k + 16 <= cipherLen) {
            byte[] cellCipher = new byte[16];
            System.arraycopy(ciphertext, k, cellCipher, 0, 16);
            byte[] cellPlain = decode16(cellCipher, key);
            System.arraycopy(cellPlain, 0, plaintext, k, cellPlain.length);
            k += 16;
        }
        return plaintext;
    }

    /**
     * 解密，获得明文字符串
     *
     * @param ciphertext 内容
     * @param code       编码
     * @return
     */
    public static String decodeSMS4toString(String ciphertext, String code) throws Exception {
        if (!StringUtils.hasText(ciphertext)) {
            return null;
        }
        byte[] bytes = ConvertUtil.hexStringToBytes(ciphertext);
        byte[] plaintext = decodeSMS4(bytes, KEY_);

        return decryptDES(plaintext, code);
    }

    /**
     * 解密，获得明文字符串
     *
     * @param ciphertext 内容
     * @param key        秘钥
     * @param code       编码
     * @return
     */
    public static String decodeSMS4toString(String ciphertext, String key, String code) throws Exception {
        if (!StringUtils.hasText(ciphertext)) {
            return null;
        }
        byte[] bytes = ConvertUtil.hexStringToBytes(ciphertext);
        byte[] plaintext = decodeSMS4(bytes, key);

        return decryptDES(plaintext, code);
    }

    private static byte[] encode16(byte[] plaintext, String key) {
        byte[] key_ = null;
        if (!StringUtils.hasText(key)) {
            key_ = KEY_.getBytes();
        } else {
            key_ = key.getBytes();
        }

        byte[] cipher = new byte[16];
        SM4Util sm4 = new SM4Util();
        sm4.sms4(plaintext, 16, key_, cipher, ENCRYPT);
        return cipher;
    }

    /**
     * 只加密16位明文
     *
     * @param plaintext
     * @param key
     * @return
     */
    private static byte[] x(byte[] plaintext, String key) {
        byte[] key_ = null;
        if (!StringUtils.hasText(key)) {
            key_ = KEY_.getBytes();
        } else {
            key_ = key.getBytes();
        }

        byte[] cipher = new byte[16];
        SM4Util sm4 = new SM4Util();
        sm4.sms4(plaintext, 16, key_, cipher, ENCRYPT);
        return cipher;
    }

    /**
     * 只解密16位密文
     *
     * @param ciphertext
     * @param key
     * @return
     */
    private static byte[] decode16(byte[] ciphertext, String key) {
        byte[] plain = new byte[16];
        SM4Util sm4 = new SM4Util();
        sm4.sms4(ciphertext, 16, key.getBytes(), plain, DECRYPT);
        return plain;
    }

    private int sms4(byte[] in, int inLen, byte[] key, byte[] out, int CryptFlag) {
        int point = 0;
        int[] round_key = new int[ROUND];
        SMS4KeyExt(key, round_key, CryptFlag);
        byte[] input;
        byte[] output = new byte[16];

        while (inLen >= BLOCK) {
            input = Arrays.copyOfRange(in, point, point + 16);
            SMS4Crypt(input, output, round_key);
            System.arraycopy(output, 0, out, point, BLOCK);
            inLen -= BLOCK;
            point += BLOCK;
        }

        return 0;
    }

    private int Rotl(int x, int y) {
        return x << y | x >>> (32 - y);
    }

    private int ByteSub(int A) {
        return (Sbox[A >>> 24 & 0xFF] & 0xFF) << 24 | (Sbox[A >>> 16 & 0xFF] & 0xFF) << 16
                | (Sbox[A >>> 8 & 0xFF] & 0xFF) << 8 | (Sbox[A & 0xFF] & 0xFF);
    }

    private int L1(int B) {
        return B ^ Rotl(B, 2) ^ Rotl(B, 10) ^ Rotl(B, 18) ^ Rotl(B, 24);
    }

    private int L2(int B) {
        return B ^ Rotl(B, 13) ^ Rotl(B, 23);
    }

    private void SMS4Crypt(byte[] Input, byte[] Output, int[] rk) {
        int r, mid, x0, x1, x2, x3;
        int[] x = new int[4];
        int[] tmp = new int[4];
        for (int i = 0; i < 4; i++) {
            tmp[0] = Input[4 * i] & 0xff;
            tmp[1] = Input[1 + 4 * i] & 0xff;
            tmp[2] = Input[2 + 4 * i] & 0xff;
            tmp[3] = Input[3 + 4 * i] & 0xff;
            x[i] = tmp[0] << 24 | tmp[1] << 16 | tmp[2] << 8 | tmp[3];
        }
        for (r = 0; r < 32; r += 4) {
            mid = x[1] ^ x[2] ^ x[3] ^ rk[r];
            mid = ByteSub(mid);
            x[0] = x[0] ^ L1(mid); // x4

            mid = x[2] ^ x[3] ^ x[0] ^ rk[r + 1];
            mid = ByteSub(mid);
            x[1] = x[1] ^ L1(mid); // x5

            mid = x[3] ^ x[0] ^ x[1] ^ rk[r + 2];
            mid = ByteSub(mid);
            x[2] = x[2] ^ L1(mid); // x6

            mid = x[0] ^ x[1] ^ x[2] ^ rk[r + 3];
            mid = ByteSub(mid);
            x[3] = x[3] ^ L1(mid); // x7
        }

        // Reverse
        for (int j = 0; j < 16; j += 4) {
            Output[j] = (byte) (x[3 - j / 4] >>> 24 & 0xFF);
            Output[j + 1] = (byte) (x[3 - j / 4] >>> 16 & 0xFF);
            Output[j + 2] = (byte) (x[3 - j / 4] >>> 8 & 0xFF);
            Output[j + 3] = (byte) (x[3 - j / 4] & 0xFF);
        }
    }

    private void SMS4KeyExt(byte[] Key, int[] rk, int CryptFlag) {
        int r, mid;
        int[] x = new int[4];
        int[] tmp = new int[4];
        for (int i = 0; i < 4; i++) {
            tmp[0] = Key[4 * i] & 0xFF;
            tmp[1] = Key[1 + 4 * i] & 0xff;
            tmp[2] = Key[2 + 4 * i] & 0xff;
            tmp[3] = Key[3 + 4 * i] & 0xff;
            x[i] = tmp[0] << 24 | tmp[1] << 16 | tmp[2] << 8 | tmp[3];
        }
        x[0] ^= 0xa3b1bac6;
        x[1] ^= 0x56aa3350;
        x[2] ^= 0x677d9197;
        x[3] ^= 0xb27022dc;
        for (r = 0; r < 32; r += 4) {
            mid = x[1] ^ x[2] ^ x[3] ^ CK[r];
            mid = ByteSub(mid);
            rk[r] = x[0] ^= L2(mid); // rk0=K4

            mid = x[2] ^ x[3] ^ x[0] ^ CK[r + 1];
            mid = ByteSub(mid);
            rk[r + 1] = x[1] ^= L2(mid); // rk1=K5

            mid = x[3] ^ x[0] ^ x[1] ^ CK[r + 2];
            mid = ByteSub(mid);
            rk[r + 2] = x[2] ^= L2(mid); // rk2=K6

            mid = x[0] ^ x[1] ^ x[2] ^ CK[r + 3];
            mid = ByteSub(mid);
            rk[r + 3] = x[3] ^= L2(mid); // rk3=K7
        }

        // 解密时轮密钥使用顺序：rk31,rk30,...,rk0
        if (CryptFlag == DECRYPT) {
            for (r = 0; r < 16; r++) {
                mid = rk[r];
                rk[r] = rk[31 - r];
                rk[31 - r] = mid;
            }
        }
    }


    /**
     * Str转16位
     *
     * @param encryptString
     * @return
     */
    private static String encryptDES(String encryptString) throws Exception {
        IvParameterSpec zeroIv = new IvParameterSpec(iv);
        SecretKeySpec key = new SecretKeySpec(PASSWORD_CRYPT_KEY.getBytes(), "DES");
        Cipher cipher = Cipher.getInstance("DES/CBC/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE, key, zeroIv);
        byte[] encryptedData = cipher.doFinal(encryptString.getBytes());
        String hexString = parseByte2HexStr(encryptedData);
        return hexString;
        // return Base64.encode(encryptedData);
    }

    /**
     * 16位转str
     *
     * @param decrypt
     * @param code
     * @return
     */
    private static String decryptDES(byte[] decrypt, String code) throws Exception {
        byte[] byteMi = hex2byte(decrypt);
        IvParameterSpec zeroIv = new IvParameterSpec(iv);
        SecretKeySpec key = new SecretKeySpec(PASSWORD_CRYPT_KEY.getBytes(), "DES");
        Cipher cipher = Cipher.getInstance("DES/CBC/PKCS5Padding");
        cipher.init(Cipher.DECRYPT_MODE, key, zeroIv);
        byte decryptedData[] = cipher.doFinal(byteMi);
        if (!StringUtils.hasText(code)) {
            code = CODE_UTF8;
        }
        return new String(decryptedData, code);
    }

    private static String parseByte2HexStr(byte buf[]) {
        StringBuffer sb = new StringBuffer();
        for (int i = 0; i < buf.length; i++) {
            String hex = Integer.toHexString(buf[i] & 0xFF);
            if (hex.length() == 1) {
                hex = '0' + hex;
            }
            sb.append(hex.toUpperCase());
        }
        return sb.toString();
    }

    private static byte[] hex2byte(byte[] b) {
        if ((b.length % 2) != 0) {
            throw new IllegalArgumentException("长度不是偶数");
        }
        byte[] b2 = new byte[b.length / 2];
        for (int n = 0; n < b.length; n += 2) {
            String item = new String(b, n, 2);
            b2[n / 2] = (byte) Integer.parseInt(item, 16);
        }
        return b2;
    }

    private SM4Util() {
    }
}