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Dahua ICC Open API SDK for Java
There is a newer version: 1.0.13.7
package com.dahuatech.hutool.core.codec;

/**
 * RotN（rotate by N places），回转N位密码，是一种简易的替换式密码，也是过去在古罗马开发的凯撒加密的一种变体。

 * 代码来自：https://github.com/orclight/jencrypt
 *
 * @author looly,shuzhilong
 * @since 4.4.1
 */
public class Rot {

  private static final char aCHAR = 'a';
  private static final char zCHAR = 'z';
  private static final char ACHAR = 'A';
  private static final char ZCHAR = 'Z';
  private static final char CHAR0 = '0';
  private static final char CHAR9 = '9';

  /**
   * Rot-13编码，同时编码数字
   *
   * @param message 被编码的消息
   * @return 编码后的字符串
   */
  public static String encode13(String message) {
    return encode13(message, true);
  }

  /**
   * Rot-13编码
   *
   * @param message 被编码的消息
   * @param isEnocdeNumber 是否编码数字
   * @return 编码后的字符串
   */
  public static String encode13(String message, boolean isEnocdeNumber) {
    return encode(message, 13, isEnocdeNumber);
  }

  /**
   * RotN编码
   *
   * @param message 被编码的消息
   * @param offset 位移，常用位移13
   * @param isEnocdeNumber 是否编码数字
   * @return 编码后的字符串
   */
  public static String encode(String message, int offset, boolean isEnocdeNumber) {
    final int len = message.length();
    final char[] chars = new char[len];

    for (int i = 0; i < len; i++) {
      chars[i] = encodeChar(message.charAt(i), offset, isEnocdeNumber);
    }
    return new String(chars);
  }

  /**
   * Rot-13解码，同时解码数字
   *
   * @param rot 被解码的消息密文
   * @return 解码后的字符串
   */
  public static String decode13(String rot) {
    return decode13(rot, true);
  }

  /**
   * Rot-13解码
   *
   * @param rot 被解码的消息密文
   * @param isDecodeNumber 是否解码数字
   * @return 解码后的字符串
   */
  public static String decode13(String rot, boolean isDecodeNumber) {
    return decode(rot, 13, isDecodeNumber);
  }

  /**
   * RotN解码
   *
   * @param rot 被解码的消息密文
   * @param offset 位移，常用位移13
   * @param isDecodeNumber 是否解码数字
   * @return 解码后的字符串
   */
  public static String decode(String rot, int offset, boolean isDecodeNumber) {
    final int len = rot.length();
    final char[] chars = new char[len];

    for (int i = 0; i < len; i++) {
      chars[i] = decodeChar(rot.charAt(i), offset, isDecodeNumber);
    }
    return new String(chars);
  }

  // ------------------------------------------------------------------------------------------
  // Private method start
  /**
   * 解码字符
   *
   * @param c 字符
   * @param offset 位移
   * @param isDecodeNumber 是否解码数字
   * @return 解码后的字符串
   */
  private static char encodeChar(char c, int offset, boolean isDecodeNumber) {
    if (isDecodeNumber) {
      if (c >= CHAR0 && c <= CHAR9) {
        c -= CHAR0;
        c = (char) ((c + offset) % 10);
        c += CHAR0;
      }
    }

    // A == 65, Z == 90
    if (c >= ACHAR && c <= ZCHAR) {
      c -= ACHAR;
      c = (char) ((c + offset) % 26);
      c += ACHAR;
    }
    // a == 97, z == 122.
    else if (c >= aCHAR && c <= zCHAR) {
      c -= aCHAR;
      c = (char) ((c + offset) % 26);
      c += aCHAR;
    }
    return c;
  }

  /**
   * 编码字符
   *
   * @param c 字符
   * @param offset 位移
   * @param isDecodeNumber 是否编码数字
   * @return 编码后的字符串
   */
  private static char decodeChar(char c, int offset, boolean isDecodeNumber) {
    int temp = c;
    // if converting numbers is enabled
    if (isDecodeNumber) {
      if (temp >= CHAR0 && temp <= CHAR9) {
        temp -= CHAR0;
        temp = temp - offset;
        while (temp < 0) {
          temp += 10;
        }
        temp += CHAR0;
      }
    }

    // A == 65, Z == 90
    if (temp >= ACHAR && temp <= ZCHAR) {
      temp -= ACHAR;

      temp = temp - offset;
      while (temp < 0) {
        temp = 26 + temp;
      }
      temp += ACHAR;
    } else if (temp >= aCHAR && temp <= zCHAR) {
      temp -= aCHAR;

      temp = temp - offset;
      if (temp < 0) temp = 26 + temp;

      temp += aCHAR;
    }
    return (char) temp;
  }
  // ------------------------------------------------------------------------------------------
  // Private method end
}