Detailed explanation of the reversible encryption algorithm that can be shared by PHP and C#, _PHP tutorial

<&#63;php
class DES
{
  var $key;
  var $iv; //偏移量
  
  function DES($key = '11001100', $iv=0 ) {
  //key长度8例如:1234abcd
    $this->key = $key;
    if( $iv == 0 ) {
      $this->iv = $key; //默认以$key 作为 iv
    } else {
      $this->iv = $iv; //mcrypt_create_iv ( mcrypt_get_block_size (MCRYPT_DES, MCRYPT_MODE_CBC), MCRYPT_DEV_RANDOM );
    }
  }
  
  function encrypt($str) {
  //加密，返回大写十六进制字符串
    $size = mcrypt_get_block_size ( MCRYPT_DES, MCRYPT_MODE_CBC );
    $str = $this->pkcs5Pad ( $str, $size );
    return strtoupper( bin2hex( mcrypt_cbc(MCRYPT_DES, $this->key, $str, MCRYPT_ENCRYPT, $this->iv ) ) );
  }
  
  function decrypt($str) {
  //解密
    $strBin = $this->hex2bin( strtolower( $str ) );
    $str = mcrypt_cbc( MCRYPT_DES, $this->key, $strBin, MCRYPT_DECRYPT, $this->iv );
    $str = $this->pkcs5Unpad( $str );
    return $str;
  }
  
  function hex2bin($hexData) {
    $binData = "";
    for($i = 0; $i < strlen ( $hexData ); $i += 2) {
      $binData .= chr ( hexdec ( substr ( $hexData, $i, 2 ) ) );
    }
    return $binData;
  }

  function pkcs5Pad($text, $blocksize) {
    $pad = $blocksize - (strlen ( $text ) % $blocksize);
    return $text . str_repeat ( chr ( $pad ), $pad );
  }
  
  function pkcs5Unpad($text) {
    $pad = ord ( $text {strlen ( $text ) - 1} );
    if ($pad > strlen ( $text ))
      return false;
    if (strspn ( $text, chr ( $pad ), strlen ( $text ) - $pad ) != $pad)
      return false;
    return substr ( $text, 0, - 1 * $pad );
  }
  
}
&#63;>

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;
using System.Text;

namespace WindowsFormsApplication1
{
  /// <summary>
  /// DES加密解密字符串
  /// </summary>
  public class DesEncryption
  {
    /// <summary>
    /// DES加密字符串
    /// </summary>
    /// <param name="encryptString">待加密的字符串</param>
    /// <param name="encryptKey">加密密钥,要求为8位</param>
    /// <returns>加密成功返回加密后的字符串，失败返回null</returns>
    public static string EncryptDES(string encryptString, string encryptKey = "11001100")
    {
      try
      {
        byte[] rgbKey = ASCIIEncoding.ASCII.GetBytes(encryptKey.Substring(0, 8));
        byte[] rgbIV = rgbKey;
        byte[] inputByteArray = Encoding.UTF8.GetBytes(encryptString);
        DESCryptoServiceProvider dCSP = new DESCryptoServiceProvider();
        MemoryStream mStream = new MemoryStream();
        CryptoStream cStream = new CryptoStream(mStream, dCSP.CreateEncryptor(rgbKey, rgbIV), CryptoStreamMode.Write);
        cStream.Write(inputByteArray, 0, inputByteArray.Length);
        cStream.FlushFinalBlock();
        StringBuilder ret = new StringBuilder();
        foreach (byte b in mStream.ToArray())
        {
          ret.AppendFormat("{0:X2}", b);
        }
        ret.ToString();
        return ret.ToString(); 
      }
      catch
      {
        return null;
      }
    }

    /// <summary>
    /// DES解密字符串
    /// </summary>
    /// <param name="decryptString">待解密的字符串</param>
    /// <param name="decryptKey">解密密钥,要求为8位,和加密密钥相同</param>
    /// <returns>解密成功返回解密后的字符串，失败返回null</returns>
    public static string DecryptDES(string decryptString, string decryptKey = "11001100")
    {
      try
      {
        byte[] rgbKey = ASCIIEncoding.ASCII.GetBytes(decryptKey);
        byte[] rgbIV = rgbKey;
        byte[] inputByteArray = new byte[decryptString.Length / 2];
        for (int x = 0; x < decryptString.Length / 2; x++)
        {
          int i = (Convert.ToInt32(decryptString.Substring(x * 2, 2), 16));
          inputByteArray[x] = (byte)i;
        }      
        DESCryptoServiceProvider DCSP = new DESCryptoServiceProvider();
        MemoryStream mStream = new MemoryStream();
        CryptoStream cStream = new CryptoStream(mStream, DCSP.CreateDecryptor(rgbKey, rgbIV), CryptoStreamMode.Write);
        cStream.Write(inputByteArray, 0, inputByteArray.Length);
        cStream.FlushFinalBlock();
        return Encoding.UTF8.GetString(mStream.ToArray());
      }
      catch
      {
        return null;
      }
    }
  }
}