encrypt.php | searchcode

/administrator/components/com_akeeba/akeeba/utils/encrypt.php

https://bitbucket.org/organicdevelopment/joomla-2.5
PHP | 456 lines | 277 code | 59 blank | 120 comment | 64 complexity | ba07cca214260c9474b4cc817a93fdcb MD5 | raw file
Possible License(s): LGPL-3.0, GPL-2.0, MIT, BSD-3-Clause, LGPL-2.1

<?php
/**
 * @package AkeebaBackup
 * @copyright Copyright (c)2009-2012 Nicholas K. Dionysopoulos
 * @license GNU General Public License version 3, or later
 * @version $Id: encrypt.php 422 2011-01-31 09:39:33Z nikosdion $
 * @since 3.0
 */

// Protection against direct access
defined('AKEEBAENGINE') or die('Restricted access');

/**
 * AES implementation in PHP (c) Chris Veness 2005-2011.
 * 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
 */
class AEUtilEncrypt
{
	// 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];
	    } else if ($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;
	}

}