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Dahua ICC Open API SDK for Java
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package com.dahuatech.hutool.crypto.symmetric;

import com.dahuatech.hutool.core.codec.Base64;
import com.dahuatech.hutool.core.util.CharsetUtil;
import com.dahuatech.hutool.core.util.HexUtil;
import com.dahuatech.hutool.core.util.StrUtil;
import com.dahuatech.hutool.crypto.CryptoException;

import java.io.Serializable;
import java.nio.charset.Charset;
import java.util.concurrent.locks.ReentrantReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock.ReadLock;
import java.util.concurrent.locks.ReentrantReadWriteLock.WriteLock;

/**
 * RC4加密解密算法实现

 * 来自：https://github.com/xSAVIKx/RC4-cipher/blob/master/src/main/java/com/github/xsavikx/rc4/RC4.java
 *
 * @author Iurii Sergiichuk，Looly
 */
public class RC4 implements Serializable {
  private static final long serialVersionUID = 1L;

  private static final int SBOX_LENGTH = 256;
  /** 密钥最小长度 */
  private static final int KEY_MIN_LENGTH = 5;
  private final ReentrantReadWriteLock lock = new ReentrantReadWriteLock();
  /** Sbox */
  private int[] sbox;

  /**
   * 构造
   *
   * @param key 密钥
   * @throws CryptoException key长度小于5或者大于255抛出此异常
   */
  public RC4(String key) throws CryptoException {
    setKey(key);
  }

  /**
   * 加密
   *
   * @param message 消息
   * @param charset 编码
   * @return 密文
   * @throws CryptoException key长度小于5或者大于255抛出此异常
   */
  public byte[] encrypt(String message, Charset charset) throws CryptoException {
    return crypt(StrUtil.bytes(message, charset));
  }

  /**
   * 加密，使用默认编码：UTF-8
   *
   * @param message 消息
   * @return 密文
   * @throws CryptoException key长度小于5或者大于255抛出此异常
   */
  public byte[] encrypt(String message) throws CryptoException {
    return encrypt(message, CharsetUtil.CHARSET_UTF_8);
  }

  /**
   * 加密
   *
   * @param data 数据
   * @return 加密后的Hex
   * @since 4.5.12
   */
  public String encryptHex(byte[] data) {
    return HexUtil.encodeHexStr(crypt(data));
  }

  /**
   * 加密
   *
   * @param data 数据
   * @return 加密后的Base64
   * @since 4.5.12
   */
  public String encryptBase64(byte[] data) {
    return Base64.encode(crypt(data));
  }

  /**
   * 加密
   *
   * @param data 被加密的字符串
   * @param charset 编码
   * @return 加密后的Hex
   * @since 4.5.12
   */
  public String encryptHex(String data, Charset charset) {
    return HexUtil.encodeHexStr(encrypt(data, charset));
  }

  /**
   * 加密
   *
   * @param data 被加密的字符串
   * @param charset 编码
   * @return 加密后的Base64
   * @since 4.5.12
   */
  public String encryptBase64(String data, Charset charset) {
    return Base64.encode(encrypt(data, charset));
  }

  /**
   * 解密
   *
   * @param message 消息
   * @param charset 编码
   * @return 明文
   * @throws CryptoException key长度小于5或者大于255抛出此异常
   */
  public String decrypt(byte[] message, Charset charset) throws CryptoException {
    return StrUtil.str(crypt(message), charset);
  }

  /**
   * 解密，使用默认编码UTF-8
   *
   * @param message 消息
   * @return 明文
   * @throws CryptoException key长度小于5或者大于255抛出此异常
   */
  public String decrypt(byte[] message) throws CryptoException {
    return decrypt(message, CharsetUtil.CHARSET_UTF_8);
  }

  /**
   * 加密或解密指定值，调用此方法前需初始化密钥
   *
   * @param msg 要加密或解密的消息
   * @return 加密或解密后的值
   */
  public byte[] crypt(final byte[] msg) {
    final ReadLock readLock = this.lock.readLock();
    readLock.lock();
    byte[] code;
    try {
      final int[] sbox = this.sbox.clone();
      code = new byte[msg.length];
      int i = 0;
      int j = 0;
      for (int n = 0; n < msg.length; n++) {
        i = (i + 1) % SBOX_LENGTH;
        j = (j + sbox[i]) % SBOX_LENGTH;
        swap(i, j, sbox);
        int rand = sbox[(sbox[i] + sbox[j]) % SBOX_LENGTH];
        code[n] = (byte) (rand ^ msg[n]);
      }
    } finally {
      readLock.unlock();
    }
    return code;
  }

  /**
   * 设置密钥
   *
   * @param key 密钥
   * @throws CryptoException key长度小于5或者大于255抛出此异常
   */
  public void setKey(String key) throws CryptoException {
    final int length = key.length();
    if (length < KEY_MIN_LENGTH || length >= SBOX_LENGTH) {
      throw new CryptoException(
          "Key length has to be between {} and {}", KEY_MIN_LENGTH, (SBOX_LENGTH - 1));
    }

    final WriteLock writeLock = this.lock.writeLock();
    writeLock.lock();
    try {
      this.sbox = initSBox(StrUtil.utf8Bytes(key));
    } finally {
      writeLock.unlock();
    }
  }

  // ----------------------------------------------------------------------------------------------------------------------- Private method start
  /**
   * 初始化Sbox
   *
   * @param key 密钥
   * @return sbox
   */
  private int[] initSBox(byte[] key) {
    int[] sbox = new int[SBOX_LENGTH];
    int j = 0;

    for (int i = 0; i < SBOX_LENGTH; i++) {
      sbox[i] = i;
    }

    for (int i = 0; i < SBOX_LENGTH; i++) {
      j = (j + sbox[i] + (key[i % key.length]) & 0xFF) % SBOX_LENGTH;
      swap(i, j, sbox);
    }
    return sbox;
  }

  /**
   * 交换指定两个位置的值
   *
   * @param i 位置1
   * @param j 位置2
   * @param sbox 数组
   */
  private void swap(int i, int j, int[] sbox) {
    int temp = sbox[i];
    sbox[i] = sbox[j];
    sbox[j] = temp;
  }
  // ----------------------------------------------------------------------------------------------------------------------- Private method end
}