<?php
/**
 * @copyright Copyright (c)2009-2013 Nicholas K. Dionysopoulos
 * @license GNU General Public License version 3, or later
 *
 * @since 2.4
 */

// Protection against direct access
\defined('_JEXEC') or die;

/**
 * AES implementation in PHP (c) Chris Veness 2005-2013.
 * Right to use and adapt is granted for under a simple creative commons attribution
 * licence. No warranty of any form is offered.
 *
 * Modified for Akeeba Backup by Nicholas K. Dionysopoulos
 * Included for JCE with the kind permission of Nicholas K. Dionysopoulos
 */
class WFUtilEncrypt
{
    // Sbox is pre-computed multiplicative inverse in GF(2^8) used in SubBytes and KeyExpansion [�5.1.1]
    protected static $Sbox =
             array(0x63, 0x7c, 0x77, 0x7b, 0xf2, 0x6b, 0x6f, 0xc5, 0x30, 0x01, 0x67, 0x2b, 0xfe, 0xd7, 0xab, 0x76,
                   0xca, 0x82, 0xc9, 0x7d, 0xfa, 0x59, 0x47, 0xf0, 0xad, 0xd4, 0xa2, 0xaf, 0x9c, 0xa4, 0x72, 0xc0,
                   0xb7, 0xfd, 0x93, 0x26, 0x36, 0x3f, 0xf7, 0xcc, 0x34, 0xa5, 0xe5, 0xf1, 0x71, 0xd8, 0x31, 0x15,
                   0x04, 0xc7, 0x23, 0xc3, 0x18, 0x96, 0x05, 0x9a, 0x07, 0x12, 0x80, 0xe2, 0xeb, 0x27, 0xb2, 0x75,
                   0x09, 0x83, 0x2c, 0x1a, 0x1b, 0x6e, 0x5a, 0xa0, 0x52, 0x3b, 0xd6, 0xb3, 0x29, 0xe3, 0x2f, 0x84,
                   0x53, 0xd1, 0x00, 0xed, 0x20, 0xfc, 0xb1, 0x5b, 0x6a, 0xcb, 0xbe, 0x39, 0x4a, 0x4c, 0x58, 0xcf,
                   0xd0, 0xef, 0xaa, 0xfb, 0x43, 0x4d, 0x33, 0x85, 0x45, 0xf9, 0x02, 0x7f, 0x50, 0x3c, 0x9f, 0xa8,
                   0x51, 0xa3, 0x40, 0x8f, 0x92, 0x9d, 0x38, 0xf5, 0xbc, 0xb6, 0xda, 0x21, 0x10, 0xff, 0xf3, 0xd2,
                   0xcd, 0x0c, 0x13, 0xec, 0x5f, 0x97, 0x44, 0x17, 0xc4, 0xa7, 0x7e, 0x3d, 0x64, 0x5d, 0x19, 0x73,
                   0x60, 0x81, 0x4f, 0xdc, 0x22, 0x2a, 0x90, 0x88, 0x46, 0xee, 0xb8, 0x14, 0xde, 0x5e, 0x0b, 0xdb,
                   0xe0, 0x32, 0x3a, 0x0a, 0x49, 0x06, 0x24, 0x5c, 0xc2, 0xd3, 0xac, 0x62, 0x91, 0x95, 0xe4, 0x79,
                   0xe7, 0xc8, 0x37, 0x6d, 0x8d, 0xd5, 0x4e, 0xa9, 0x6c, 0x56, 0xf4, 0xea, 0x65, 0x7a, 0xae, 0x08,
                   0xba, 0x78, 0x25, 0x2e, 0x1c, 0xa6, 0xb4, 0xc6, 0xe8, 0xdd, 0x74, 0x1f, 0x4b, 0xbd, 0x8b, 0x8a,
                   0x70, 0x3e, 0xb5, 0x66, 0x48, 0x03, 0xf6, 0x0e, 0x61, 0x35, 0x57, 0xb9, 0x86, 0xc1, 0x1d, 0x9e,
                   0xe1, 0xf8, 0x98, 0x11, 0x69, 0xd9, 0x8e, 0x94, 0x9b, 0x1e, 0x87, 0xe9, 0xce, 0x55, 0x28, 0xdf,
                   0x8c, 0xa1, 0x89, 0x0d, 0xbf, 0xe6, 0x42, 0x68, 0x41, 0x99, 0x2d, 0x0f, 0xb0, 0x54, 0xbb, 0x16, );

    // Rcon is Round Constant used for the Key Expansion [1st col is 2^(r-1) in GF(2^8)] [�5.2]
    protected static $Rcon = array(
                   array(0x00, 0x00, 0x00, 0x00),
                   array(0x01, 0x00, 0x00, 0x00),
                   array(0x02, 0x00, 0x00, 0x00),
                   array(0x04, 0x00, 0x00, 0x00),
                   array(0x08, 0x00, 0x00, 0x00),
                   array(0x10, 0x00, 0x00, 0x00),
                   array(0x20, 0x00, 0x00, 0x00),
                   array(0x40, 0x00, 0x00, 0x00),
                   array(0x80, 0x00, 0x00, 0x00),
                   array(0x1b, 0x00, 0x00, 0x00),
                   array(0x36, 0x00, 0x00, 0x00), );

    protected static $passwords = array();

    /**
     * AES Cipher function: encrypt 'input' with Rijndael algorithm.
     *
     * @param input message as byte-array (16 bytes)
     * @param w     key schedule as 2D byte-array (Nr+1 x Nb bytes) -
     *              generated from the cipher key by KeyExpansion()
     *
     * @return ciphertext as byte-array (16 bytes)
     */
    public static function Cipher($input, $w)
    {    // main Cipher function [�5.1]
      $Nb = 4;                 // block size (in words): no of columns in state (fixed at 4 for AES)
      $Nr = count($w) / $Nb - 1; // no of rounds: 10/12/14 for 128/192/256-bit keys

      $state = array();  // initialise 4xNb byte-array 'state' with input [�3.4]
      for ($i = 0; $i < 4 * $Nb; ++$i) {
          $state[$i % 4][floor($i / 4)] = $input[$i];
      }

        $state = self::AddRoundKey($state, $w, 0, $Nb);

        for ($round = 1; $round < $Nr; ++$round) {  // apply Nr rounds
        $state = self::SubBytes($state, $Nb);
            $state = self::ShiftRows($state, $Nb);
            $state = self::MixColumns($state, $Nb);
            $state = self::AddRoundKey($state, $w, $round, $Nb);
        }

        $state = self::SubBytes($state, $Nb);
        $state = self::ShiftRows($state, $Nb);
        $state = self::AddRoundKey($state, $w, $Nr, $Nb);

        $output = array(4 * $Nb);  // convert state to 1-d array before returning [�3.4]
      for ($i = 0; $i < 4 * $Nb; ++$i) {
          $output[$i] = $state[$i % 4][floor($i / 4)];
      }

        return $output;
    }

    protected static function AddRoundKey($state, $w, $rnd, $Nb)
    {  // xor Round Key into state S [�5.1.4]
      for ($r = 0; $r < 4; ++$r) {
          for ($c = 0; $c < $Nb; ++$c) {
              $state[$r][$c] ^= $w[$rnd * 4 + $c][$r];
          }
      }

        return $state;
    }

    protected static function SubBytes($s, $Nb)
    {    // apply SBox to state S [�5.1.1]
      for ($r = 0; $r < 4; ++$r) {
          for ($c = 0; $c < $Nb; ++$c) {
              $s[$r][$c] = self::$Sbox[$s[$r][$c]];
          }
      }

        return $s;
    }

    protected static function ShiftRows($s, $Nb)
    {    // shift row r of state S left by r bytes [�5.1.2]
      $t = array(4);
        for ($r = 1; $r < 4; ++$r) {
            for ($c = 0; $c < 4; ++$c) {
                $t[$c] = $s[$r][($c + $r) % $Nb];
            }  // shift into temp copy
        for ($c = 0; $c < 4; ++$c) {
            $s[$r][$c] = $t[$c];
        }         // and copy back
        }          // note that this will work for Nb=4,5,6, but not 7,8 (always 4 for AES):
      return $s;  // see fp.gladman.plus.com/cryptography_technology/rijndael/aes.spec.311.pdf
    }

    protected static function MixColumns($s, $Nb)
    {   // combine bytes of each col of state S [�5.1.3]
      for ($c = 0; $c < 4; ++$c) {
          $a = array(4);  // 'a' is a copy of the current column from 's'
        $b = array(4);  // 'b' is a�{02} in GF(2^8)
        for ($i = 0; $i < 4; ++$i) {
            $a[$i] = $s[$i][$c];
            $b[$i] = $s[$i][$c] & 0x80 ? $s[$i][$c] << 1 ^ 0x011b : $s[$i][$c] << 1;
        }
        // a[n] ^ b[n] is a�{03} in GF(2^8)
        $s[0][$c] = $b[0] ^ $a[1] ^ $b[1] ^ $a[2] ^ $a[3]; // 2*a0 + 3*a1 + a2 + a3
        $s[1][$c] = $a[0] ^ $b[1] ^ $a[2] ^ $b[2] ^ $a[3]; // a0 * 2*a1 + 3*a2 + a3
        $s[2][$c] = $a[0] ^ $a[1] ^ $b[2] ^ $a[3] ^ $b[3]; // a0 + a1 + 2*a2 + 3*a3
        $s[3][$c] = $a[0] ^ $b[0] ^ $a[1] ^ $a[2] ^ $b[3]; // 3*a0 + a1 + a2 + 2*a3
      }

        return $s;
    }

    /**
     * Key expansion for Rijndael Cipher(): performs key expansion on cipher key
     * to generate a key schedule.
     *
     * @param key cipher key byte-array (16 bytes)
     *
     * @return key schedule as 2D byte-array (Nr+1 x Nb bytes)
     */
    public static function KeyExpansion($key)
    {  // generate Key Schedule from Cipher Key [�5.2]
      $Nb = 4;              // block size (in words): no of columns in state (fixed at 4 for AES)
      $Nk = count($key) / 4;  // key length (in words): 4/6/8 for 128/192/256-bit keys
      $Nr = $Nk + 6;        // no of rounds: 10/12/14 for 128/192/256-bit keys

      $w = array();
        $temp = array();

        for ($i = 0; $i < $Nk; ++$i) {
            $r = array($key[4 * $i], $key[4 * $i + 1], $key[4 * $i + 2], $key[4 * $i + 3]);
            $w[$i] = $r;
        }

        for ($i = $Nk; $i < ($Nb * ($Nr + 1)); ++$i) {
            $w[$i] = array();
            for ($t = 0; $t < 4; ++$t) {
                $temp[$t] = $w[$i - 1][$t];
            }
            if ($i % $Nk == 0) {
                $temp = self::SubWord(self::RotWord($temp));
                for ($t = 0; $t < 4; ++$t) {
                    $temp[$t] ^= self::$Rcon[$i / $Nk][$t];
                }
            } elseif ($Nk > 6 && $i % $Nk == 4) {
                $temp = self::SubWord($temp);
            }
            for ($t = 0; $t < 4; ++$t) {
                $w[$i][$t] = $w[$i - $Nk][$t] ^ $temp[$t];
            }
        }

        return $w;
    }

    protected static function SubWord($w)
    {    // apply SBox to 4-byte word w
      for ($i = 0; $i < 4; ++$i) {
          $w[$i] = self::$Sbox[$w[$i]];
      }

        return $w;
    }

    protected static function RotWord($w)
    {    // rotate 4-byte word w left by one byte
      $tmp = $w[0];
        for ($i = 0; $i < 3; ++$i) {
            $w[$i] = $w[$i + 1];
        }
        $w[3] = $tmp;

        return $w;
    }

    /*
     * Unsigned right shift function, since PHP has neither >>> operator nor unsigned ints
     *
     * @param a  number to be shifted (32-bit integer)
     * @param b  number of bits to shift a to the right (0..31)
     * @return   a right-shifted and zero-filled by b bits
     */
    protected static function urs($a, $b)
    {
        $a &= 0xffffffff;
        $b &= 0x1f;  // (bounds check)
      if ($a & 0x80000000 && $b > 0) {   // if left-most bit set
        $a = ($a >> 1) & 0x7fffffff;   //   right-shift one bit & clear left-most bit
        $a = $a >> ($b - 1);           //   remaining right-shifts
      } else {                       // otherwise
        $a = ($a >> $b);               //   use normal right-shift
      }

        return $a;
    }

    /**
     * Encrypt a text using AES encryption in Counter mode of operation
     *  - see http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf.
     *
     * Unicode multi-byte character safe
     *
     * @param plaintext source text to be encrypted
     * @param password  the password to use to generate a key
     * @param nBits     number of bits to be used in the key (128, 192, or 256)
     *
     * @return encrypted text
     */
    public static function AESEncryptCtr($plaintext, $password, $nBits)
    {
        $blockSize = 16;  // block size fixed at 16 bytes / 128 bits (Nb=4) for AES
      if (!($nBits == 128 || $nBits == 192 || $nBits == 256)) {
          return '';
      }  // standard allows 128/192/256 bit keys
      // note PHP (5) gives us plaintext and password in UTF8 encoding!

      // use AES itself to encrypt password to get cipher key (using plain password as source for
      // key expansion) - gives us well encrypted key
      $nBytes = $nBits / 8;  // no bytes in key
      $pwBytes = array();
        for ($i = 0; $i < $nBytes; ++$i) {
            $pwBytes[$i] = ord(substr($password, $i, 1)) & 0xff;
        }
        $key = self::Cipher($pwBytes, self::KeyExpansion($pwBytes));
        $key = array_merge($key, array_slice($key, 0, $nBytes - 16));  // expand key to 16/24/32 bytes long

      // initialise counter block (NIST SP800-38A �B.2): millisecond time-stamp for nonce in
      // 1st 8 bytes, block counter in 2nd 8 bytes
      $counterBlock = array();
        $nonce = floor(microtime(true) * 1000);   // timestamp: milliseconds since 1-Jan-1970
      $nonceSec = floor($nonce / 1000);
        $nonceMs = $nonce % 1000;
      // encode nonce with seconds in 1st 4 bytes, and (repeated) ms part filling 2nd 4 bytes
      for ($i = 0; $i < 4; ++$i) {
          $counterBlock[$i] = self::urs($nonceSec, $i * 8) & 0xff;
      }
        for ($i = 0; $i < 4; ++$i) {
            $counterBlock[$i + 4] = $nonceMs & 0xff;
        }
      // and convert it to a string to go on the front of the ciphertext
      $ctrTxt = '';
        for ($i = 0; $i < 8; ++$i) {
            $ctrTxt .= chr($counterBlock[$i]);
        }

      // generate key schedule - an expansion of the key into distinct Key Rounds for each round
      $keySchedule = self::KeyExpansion($key);

        $blockCount = ceil(strlen($plaintext) / $blockSize);
        $ciphertxt = array();  // ciphertext as array of strings

      for ($b = 0; $b < $blockCount; ++$b) {
          // set counter (block #) in last 8 bytes of counter block (leaving nonce in 1st 8 bytes)
        // done in two stages for 32-bit ops: using two words allows us to go past 2^32 blocks (68GB)
        for ($c = 0; $c < 4; ++$c) {
            $counterBlock[15 - $c] = self::urs($b, $c * 8) & 0xff;
        }
          for ($c = 0; $c < 4; ++$c) {
              $counterBlock[15 - $c - 4] = self::urs($b / 0x100000000, $c * 8);
          }

          $cipherCntr = self::Cipher($counterBlock, $keySchedule);  // -- encrypt counter block --

        // block size is reduced on final block
        $blockLength = $b < $blockCount - 1 ? $blockSize : (strlen($plaintext) - 1) % $blockSize + 1;
          $cipherByte = array();

          for ($i = 0; $i < $blockLength; ++$i) {  // -- xor plaintext with ciphered counter byte-by-byte --
          $cipherByte[$i] = $cipherCntr[$i] ^ ord(substr($plaintext, $b * $blockSize + $i, 1));
              $cipherByte[$i] = chr($cipherByte[$i]);
          }
          $ciphertxt[$b] = implode('', $cipherByte);  // escape troublesome characters in ciphertext
      }

      // implode is more efficient than repeated string concatenation
      $ciphertext = $ctrTxt.implode('', $ciphertxt);
        $ciphertext = base64_encode($ciphertext);

        return $ciphertext;
    }

    /**
     * Decrypt a text encrypted by AES in counter mode of operation.
     *
     * @param ciphertext source text to be decrypted
     * @param password   the password to use to generate a key
     * @param nBits      number of bits to be used in the key (128, 192, or 256)
     *
     * @return decrypted text
     */
    public static function AESDecryptCtr($ciphertext, $password, $nBits)
    {
        $blockSize = 16;  // block size fixed at 16 bytes / 128 bits (Nb=4) for AES
      if (!($nBits == 128 || $nBits == 192 || $nBits == 256)) {
          return '';
      }  // standard allows 128/192/256 bit keys
      $ciphertext = base64_decode($ciphertext);

      // use AES to encrypt password (mirroring encrypt routine)
      $nBytes = $nBits / 8;  // no bytes in key
      $pwBytes = array();
        for ($i = 0; $i < $nBytes; ++$i) {
            $pwBytes[$i] = ord(substr($password, $i, 1)) & 0xff;
        }
        $key = self::Cipher($pwBytes, self::KeyExpansion($pwBytes));
        $key = array_merge($key, array_slice($key, 0, $nBytes - 16));  // expand key to 16/24/32 bytes long

      // recover nonce from 1st element of ciphertext
      $counterBlock = array();
        $ctrTxt = substr($ciphertext, 0, 8);
        for ($i = 0; $i < 8; ++$i) {
            $counterBlock[$i] = ord(substr($ctrTxt, $i, 1));
        }

      // generate key schedule
      $keySchedule = self::KeyExpansion($key);

      // separate ciphertext into blocks (skipping past initial 8 bytes)
      $nBlocks = ceil((strlen($ciphertext) - 8) / $blockSize);
        $ct = array();
        for ($b = 0; $b < $nBlocks; ++$b) {
            $ct[$b] = substr($ciphertext, 8 + $b * $blockSize, 16);
        }
        $ciphertext = $ct;  // ciphertext is now array of block-length strings

      // plaintext will get generated block-by-block into array of block-length strings
      $plaintxt = array();

        for ($b = 0; $b < $nBlocks; ++$b) {
            // set counter (block #) in last 8 bytes of counter block (leaving nonce in 1st 8 bytes)
        for ($c = 0; $c < 4; ++$c) {
            $counterBlock[15 - $c] = self::urs($b, $c * 8) & 0xff;
        }
            for ($c = 0; $c < 4; ++$c) {
                $counterBlock[15 - $c - 4] = self::urs(($b + 1) / 0x100000000 - 1, $c * 8) & 0xff;
            }

            $cipherCntr = self::Cipher($counterBlock, $keySchedule);  // encrypt counter block

        $plaintxtByte = array();
            for ($i = 0; $i < strlen($ciphertext[$b]); ++$i) {
                // -- xor plaintext with ciphered counter byte-by-byte --
          $plaintxtByte[$i] = $cipherCntr[$i] ^ ord(substr($ciphertext[$b], $i, 1));
                $plaintxtByte[$i] = chr($plaintxtByte[$i]);
            }
            $plaintxt[$b] = implode('', $plaintxtByte);
        }

      // join array of blocks into single plaintext string
      $plaintext = implode('', $plaintxt);

        return $plaintext;
    }

    /**
     * AES encryption in CBC mode. This is the standard mode (the CTR methods
     * actually use Rijndael-128 in CTR mode, which - technically - isn't AES).
     * The data length is tucked as a 32-bit unsigned integer (little endian)
     * after the ciphertext. It supports AES-128, AES-192 and AES-256.
     *
     * @since 3.0.1
     *
     * @author Nicholas K. Dionysopoulos
     *
     * @param string $plaintext The data to encrypt
     * @param string $password  Encryption password
     * @param int    $nBits     Encryption key size. Can be 128, 192 or 256
     *
     * @return string The ciphertext
     */
    public static function AESEncryptCBC($plaintext, $password, $nBits = 128)
    {
        if (!($nBits == 128 || $nBits == 192 || $nBits == 256)) {
            return false;
        }  // standard allows 128/192/256 bit keys
        if (!function_exists('mcrypt_module_open')) {
            return false;
        }

            // Try to fetch cached key/iv or create them if they do not exist
        $lookupKey = $password.'-'.$nBits;
        if (array_key_exists($lookupKey, self::$passwords)) {
            $key = self::$passwords[$lookupKey]['key'];
            $iv = self::$passwords[$lookupKey]['iv'];
        } else {
            // use AES itself to encrypt password to get cipher key (using plain password as source for
            // key expansion) - gives us well encrypted key
            $nBytes = $nBits / 8;  // no bytes in key
            $pwBytes = array();
            for ($i = 0; $i < $nBytes; ++$i) {
                $pwBytes[$i] = ord(substr($password, $i, 1)) & 0xff;
            }
            $key = self::Cipher($pwBytes, self::KeyExpansion($pwBytes));
            $key = array_merge($key, array_slice($key, 0, $nBytes - 16));  // expand key to 16/24/32 bytes long
            $newKey = '';
            foreach ($key as $int) {
                $newKey .= chr($int);
            }
            $key = $newKey;

            // Create an Initialization Vector (IV) based on the password, using the same technique as for the key
            $nBytes = 16;  // AES uses a 128 -bit (16 byte) block size, hence the IV size is always 16 bytes
            $pwBytes = array();
            for ($i = 0; $i < $nBytes; ++$i) {
                $pwBytes[$i] = ord(substr($password, $i, 1)) & 0xff;
            }
            $iv = self::Cipher($pwBytes, self::KeyExpansion($pwBytes));
            $newIV = '';
            foreach ($iv as $int) {
                $newIV .= chr($int);
            }
            $iv = $newIV;

            self::$passwords[$lookupKey]['key'] = $key;
            self::$passwords[$lookupKey]['iv'] = $iv;
        }

        $td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
        mcrypt_generic_init($td, $key, $iv);
        $ciphertext = mcrypt_generic($td, $plaintext);
        mcrypt_generic_deinit($td);

        $ciphertext .= pack('V', strlen($plaintext));

        return $ciphertext;
    }

    /**
     * AES decryption in CBC mode. This is the standard mode (the CTR methods
     * actually use Rijndael-128 in CTR mode, which - technically - isn't AES).
     *
     * Supports AES-128, AES-192 and AES-256. It supposes that the last 4 bytes
     * contained a little-endian unsigned long integer representing the unpadded
     * data length.
     *
     * @since 3.0.1
     *
     * @author Nicholas K. Dionysopoulos
     *
     * @param string $ciphertext The data to encrypt
     * @param string $password   Encryption password
     * @param int    $nBits      Encryption key size. Can be 128, 192 or 256
     *
     * @return string The plaintext
     */
    public static function AESDecryptCBC($ciphertext, $password, $nBits = 128)
    {
        if (!($nBits == 128 || $nBits == 192 || $nBits == 256)) {
            return false;
        }  // standard allows 128/192/256 bit keys
        if (!function_exists('mcrypt_module_open')) {
            return false;
        }

        // Try to fetch cached key/iv or create them if they do not exist
        $lookupKey = $password.'-'.$nBits;
        if (array_key_exists($lookupKey, self::$passwords)) {
            $key = self::$passwords[$lookupKey]['key'];
            $iv = self::$passwords[$lookupKey]['iv'];
        } else {
            // use AES itself to encrypt password to get cipher key (using plain password as source for
            // key expansion) - gives us well encrypted key
            $nBytes = $nBits / 8;  // no bytes in key
            $pwBytes = array();
            for ($i = 0; $i < $nBytes; ++$i) {
                $pwBytes[$i] = ord(substr($password, $i, 1)) & 0xff;
            }
            $key = self::Cipher($pwBytes, self::KeyExpansion($pwBytes));
            $key = array_merge($key, array_slice($key, 0, $nBytes - 16));  // expand key to 16/24/32 bytes long
            $newKey = '';
            foreach ($key as $int) {
                $newKey .= chr($int);
            }
            $key = $newKey;

            // Create an Initialization Vector (IV) based on the password, using the same technique as for the key
            $nBytes = 16;  // AES uses a 128 -bit (16 byte) block size, hence the IV size is always 16 bytes
            $pwBytes = array();
            for ($i = 0; $i < $nBytes; ++$i) {
                $pwBytes[$i] = ord(substr($password, $i, 1)) & 0xff;
            }
            $iv = self::Cipher($pwBytes, self::KeyExpansion($pwBytes));
            $newIV = '';
            foreach ($iv as $int) {
                $newIV .= chr($int);
            }
            $iv = $newIV;

            self::$passwords[$lookupKey]['key'] = $key;
            self::$passwords[$lookupKey]['iv'] = $iv;
        }

        // Read the data size
        $data_size = unpack('V', substr($ciphertext, -4));

        // Decrypt
        $td = mcrypt_module_open(MCRYPT_RIJNDAEL_128, '', MCRYPT_MODE_CBC, '');
        mcrypt_generic_init($td, $key, $iv);
        $plaintext = mdecrypt_generic($td, substr($ciphertext, 0, -4));
        mcrypt_generic_deinit($td);

        // Trim padding, if necessary
        if (strlen($plaintext) > $data_size) {
            $plaintext = substr($plaintext, 0, $data_size);
        }

        return $plaintext;
    }
}
