?php
/* 
 * By julying.com
 */
define('CRYPT_RC4_MODE_INTERNAL', 1);
define('CRYPT_RC4_MODE_MCRYPT', 2);
define('CRYPT_RC4_ENCRYPT', 0);
define('CRYPT_RC4_DECRYPT', 1);
class Crypt_RC4 {
 /**
  * The Key
  *
  * @see Crypt_RC4::setKey()
  * @var String
  * @access private
  */
 var $key = "\0";
 /**
  * The Key Stream for encryption
  *
  * If CRYPT_RC4_MODE == CRYPT_RC4_MODE_MCRYPT, this will be equal to the mcrypt object
  *
  * @see Crypt_RC4::setKey()
  * @var Array
  * @access private
  */
 var $encryptStream = false;
 /**
  * The Key Stream for decryption
  *
  * If CRYPT_RC4_MODE == CRYPT_RC4_MODE_MCRYPT, this will be equal to the mcrypt object
  *
  * @see Crypt_RC4::setKey()
  * @var Array
  * @access private
  */
 var $decryptStream = false;
 /**
  * The $i and $j indexes for encryption
  *
  * @see Crypt_RC4::_crypt()
  * @var Integer
  * @access private
  */
 var $encryptIndex = 0;
 /**
  * The $i and $j indexes for decryption
  *
  * @see Crypt_RC4::_crypt()
  * @var Integer
  * @access private
  */
 var $decryptIndex = 0;
 /**
  * MCrypt parameters
  *
  * @see Crypt_RC4::setMCrypt()
  * @var Array
  * @access private
  */
 var $mcrypt = array('', '');
 /**
  * The Encryption Algorithm
  *
  * Only used if CRYPT_RC4_MODE == CRYPT_RC4_MODE_MCRYPT. Only possible values are MCRYPT_RC4 or MCRYPT_ARCFOUR.
  *
  * @see Crypt_RC4::Crypt_RC4()
  * @var Integer
  * @access private
  */
 var $mode;
 /**
  * Default Constructor.
  *
  * Determines whether or not the mcrypt extension should be used.
  *
  * @param optional Integer $mode
  * @return Crypt_RC4
  * @access public
  */
 var $continuousBuffer ;
 function Crypt_RC4()
 {
  if ( !defined('CRYPT_RC4_MODE') ) {
   switch (true) {
    case extension_loaded('mcrypt')  (defined('MCRYPT_ARCFOUR') || defined('MCRYPT_RC4')):
     // i'd check to see if rc4 was supported, by doing in_array('arcfour', mcrypt_list_algorithms('')),
     // but since that can be changed after the object has been created, there doesn't seem to be
     // a lot of point...
     define('CRYPT_RC4_MODE', CRYPT_RC4_MODE_MCRYPT);
     break;
    default:
     define('CRYPT_RC4_MODE', CRYPT_RC4_MODE_INTERNAL);
   }
  }
  switch ( CRYPT_RC4_MODE ) {
   case CRYPT_RC4_MODE_MCRYPT:
    switch (true) {
     case defined('MCRYPT_ARCFOUR'):
      $this->mode = MCRYPT_ARCFOUR;
      break;
     case defined('MCRYPT_RC4');
      $this->mode = MCRYPT_RC4;
    }
  }
 }
 /**
  * Sets the key.
  *
  * Keys can be between 1 and 256 bytes long. If they are longer then 256 bytes, the first 256 bytes will
  * be used. If no key is explicitly set, it'll be assumed to be a single null byte.
  *
  * @access public
  * @param String $key
  */
 function setKey($key)
 {
  $this->key = $key;
  if ( CRYPT_RC4_MODE == CRYPT_RC4_MODE_MCRYPT ) {
   return;
  }
  $keyLength = strlen($key);
  $keyStream = array();
  for ($i = 0; $i  256; $i++) {
   $keyStream[$i] = $i;
  }
  $j = 0;
  for ($i = 0; $i  256; $i++) {
   $j = ($j + $keyStream[$i] + ord($key[$i % $keyLength]))  255;
   $temp = $keyStream[$i];
   $keyStream[$i] = $keyStream[$j];
   $keyStream[$j] = $temp;
  }
  $this->encryptIndex = $this->decryptIndex = array(0, 0);
  $this->encryptStream = $this->decryptStream = $keyStream;
 }
 /**
  * Dummy function.
  *
  * Some protocols, such as WEP, prepend an "initialization vector" to the key, effectively creating a new key [1].
  * If you need to use an initialization vector in this manner, feel free to prepend it to the key, yourself, before
  * calling setKey().
  *
  * [1] WEP's initialization vectors (IV's) are used in a somewhat insecure way. Since, in that protocol,
  * the IV's are relatively easy to predict, an attack described by
  * {@link http://www.drizzle.com/~aboba/IEEE/rc4_ksaproc.pdf Scott Fluhrer, Itsik Mantin, and Adi Shamir}
  * can be used to quickly guess at the rest of the key. The following links elaborate:
  *
  * {@link http://www.rsa.com/rsalabs/node.asp?id=2009 http://www.rsa.com/rsalabs/node.asp?id=2009}
  * {@link http://en.wikipedia.org/wiki/Related_key_attack http://en.wikipedia.org/wiki/Related_key_attack}
  *
  * @param String $iv
  * @see Crypt_RC4::setKey()
  * @access public
  */
 function setIV($iv)
 {
 }
 /**
  * Sets MCrypt parameters. (optional)
  *
  * If MCrypt is being used, empty strings will be used, unless otherwise specified.
  *
  * @link http://php.net/function.mcrypt-module-open#function.mcrypt-module-open
  * @access public
  * @param optional Integer $algorithm_directory
  * @param optional Integer $mode_directory
  */
 function setMCrypt($algorithm_directory = '', $mode_directory = '')
 {
  if ( CRYPT_RC4_MODE == CRYPT_RC4_MODE_MCRYPT ) {
   $this->mcrypt = array($algorithm_directory, $mode_directory);
   $this->_closeMCrypt();
  }
 }
 /**
  * Encrypts a message.
  *
  * @see Crypt_RC4::_crypt()
  * @access public
  * @param String $plaintext
  */
 function encrypt($plaintext)
 {
  return self::toHex($this->_crypt($plaintext, CRYPT_RC4_ENCRYPT));
 }
 /**
  * Decrypts a message.
  *
  * $this->decrypt($this->encrypt($plaintext)) == $this->encrypt($this->encrypt($plaintext)).
  * Atleast if the continuous buffer is disabled.
  *
  * @see Crypt_RC4::_crypt()
  * @access public
  * @param String $ciphertext
  */
 function decrypt($ciphertext)
 {
  $ciphertext = self::fromHex($ciphertext);
  return $this->_crypt($ciphertext, CRYPT_RC4_DECRYPT);
 }
 /**
  * Encrypts or decrypts a message.
  *
  * @see Crypt_RC4::encrypt()
  * @see Crypt_RC4::decrypt()
  * @access private
  * @param String $text
  * @param Integer $mode
  */
 function _crypt($text, $mode)
 {
  if ( CRYPT_RC4_MODE == CRYPT_RC4_MODE_MCRYPT ) {
   $keyStream = $mode == CRYPT_RC4_ENCRYPT ? 'encryptStream' : 'decryptStream';
   if ($this->$keyStream === false) {
    $this->$keyStream = mcrypt_module_open($this->mode, $this->mcrypt[0], MCRYPT_MODE_STREAM, $this->mcrypt[1]);
    mcrypt_generic_init($this->$keyStream, $this->key, '');
   } else if (!$this->continuousBuffer) {
    mcrypt_generic_init($this->$keyStream, $this->key, '');
   }
   $newText = mcrypt_generic($this->$keyStream, $text);
   if (!$this->continuousBuffer) {
    mcrypt_generic_deinit($this->$keyStream);
   }
   return $newText;
  }
  if ($this->encryptStream === false) {
   $this->setKey($this->key);
  }
  switch ($mode) {
   case CRYPT_RC4_ENCRYPT:
    $keyStream = $this->encryptStream;
    list($i, $j) = $this->encryptIndex;
    break;
   case CRYPT_RC4_DECRYPT:
    $keyStream = $this->decryptStream;
    list($i, $j) = $this->decryptIndex;
  }
  $newText = '';
  for ($k = 0; $k  strlen($text); $k++) {
   $i = ($i + 1)  255;
   $j = ($j + $keyStream[$i])  255;
   $temp = $keyStream[$i];
   $keyStream[$i] = $keyStream[$j];
   $keyStream[$j] = $temp;
   $temp = $keyStream[($keyStream[$i] + $keyStream[$j])  255];
   $newText.= chr(ord($text[$k]) ^ $temp);
  }
  if ($this->continuousBuffer) {
   switch ($mode) {
    case CRYPT_RC4_ENCRYPT:
     $this->encryptStream = $keyStream;
     $this->encryptIndex = array($i, $j);
     break;
    case CRYPT_RC4_DECRYPT:
     $this->decryptStream = $keyStream;
     $this->decryptIndex = array($i, $j);
   }
  }
  return $newText;
 }
 /**
  * Treat consecutive "packets" as if they are a continuous buffer.
  *
  * Say you have a 16-byte plaintext $plaintext. Using the default behavior, the two following code snippets
  * will yield different outputs:
  *
  * code>
  * echo $rc4->encrypt(substr($plaintext, 0, 8));
  * echo $rc4->encrypt(substr($plaintext, 8, 8));
  * /code>
  * code>
  * echo $rc4->encrypt($plaintext);
  * /code>
  *
  * The solution is to enable the continuous buffer. Although this will resolve the above discrepancy, it creates
  * another, as demonstrated with the following:
  *
  * code>
  * $rc4->encrypt(substr($plaintext, 0, 8));
  * echo $rc4->decrypt($des->encrypt(substr($plaintext, 8, 8)));
  * /code>
  * code>
  * echo $rc4->decrypt($des->encrypt(substr($plaintext, 8, 8)));
  * /code>
  *
  * With the continuous buffer disabled, these would yield the same output. With it enabled, they yield different
  * outputs. The reason is due to the fact that the initialization vector's change after every encryption /
  * decryption round when the continuous buffer is enabled. When it's disabled, they remain constant.
  *
  * Put another way, when the continuous buffer is enabled, the state of the Crypt_DES() object changes after each
  * encryption / decryption round, whereas otherwise, it'd remain constant. For this reason, it's recommended that
  * continuous buffers not be used. They do offer better security and are, in fact, sometimes required (SSH uses them),
  * however, they are also less intuitive and more likely to cause you problems.
  *
  * @see Crypt_RC4::disableContinuousBuffer()
  * @access public
  */
 function enableContinuousBuffer()
 {
  $this->continuousBuffer = true;
 }
 /**
  * Treat consecutive packets as if they are a discontinuous buffer.
  *
  * The default behavior.
  *
  * @see Crypt_RC4::enableContinuousBuffer()
  * @access public
  */
 function disableContinuousBuffer()
 {
  if ( CRYPT_RC4_MODE == CRYPT_RC4_MODE_INTERNAL ) {
   $this->encryptIndex = $this->decryptIndex = array(0, 0);
   $this->setKey($this->key);
  }
  $this->continuousBuffer = false;
 }
 /**
  * Dummy function.
  *
  * Since RC4 is a stream cipher and not a block cipher, no padding is necessary. The only reason this function is
  * included is so that you can switch between a block cipher and a stream cipher transparently.
  *
  * @see Crypt_RC4::disablePadding()
  * @access public
  */
 function enablePadding()
 {
 }
 /**
  * Dummy function.
  *
  * @see Crypt_RC4::enablePadding()
  * @access public
  */
 function disablePadding()
 {
 }
 /**
  * Class destructor.
  *
  * Will be called, automatically, if you're using PHP5. If you're using PHP4, call it yourself. Only really
  * needs to be called if mcrypt is being used.
  *
  * @access public
  */
 function __destruct()
 {
  if ( CRYPT_RC4_MODE == CRYPT_RC4_MODE_MCRYPT ) {
   $this->_closeMCrypt();
  }
 }
 /**
  * Properly close the MCrypt objects.
  *
  * @access prviate
  */
 function _closeMCrypt()
 {
  if ( $this->encryptStream !== false ) {
   if ( $this->continuousBuffer ) {
    mcrypt_generic_deinit($this->encryptStream);
   }
   mcrypt_module_close($this->encryptStream);
   $this->encryptStream = false;
  }
  if ( $this->decryptStream !== false ) {
   if ( $this->continuousBuffer ) {
    mcrypt_generic_deinit($this->decryptStream);
   }
   mcrypt_module_close($this->decryptStream);
   $this->decryptStream = false;
  }
 }
 // @function fromHex 把十六進制數轉換成字符串
 function toHex($sa , $len = 0){
  $buf = "";
  if( $len == 0 )
   $len = strlen($sa) ;
  for ($i = 0; $i  $len; $i++)
  {
   $val = dechex(ord($sa{$i}));  
   if(strlen($val) 2) 
    $val = "0".$val;
   $buf .= $val;
  }
  return $buf;
 }
 // @function fromHex 把十六進制數轉換成字符串 
 function fromHex($sa){
  $buf = "";
  $len = strlen($sa) ;
  for($i = 0; $i  $len; $i += 2){
   $val = chr(hexdec(substr($sa, $i, 2)));
   $buf .= $val;
  }
  return $buf;
 }
}

include('class.rc4crypt.php');
$rc4 = new Crypt_RC4();
$rc4 -> setKey('21sd54a1w5q');
$text = 'www.jb51.net';
echo $x = $rc4->encrypt($text);//加密
echo 'br />';
echo $rc4->decrypt( $x) ;//解密