AES.class.php

<?php
/*
*  Author: Cody Phillips
*  Company: Phillips Data
*  Website: www.phpaes.com, www.phillipsdata.com
*  File: AES.class.php
*  October 1, 2007
*
*  This software is sold as-is without any warranties, expressed or implied,
*  including but not limited to performance and/or merchantability. No
*  warranty of fitness for a particular purpose is offered. This script can
*  be used on as many servers as needed, as long as the servers are owned
*  by the purchaser. (Contact us if you want to distribute it as part of
*  another project) The purchaser cannot modify, rewrite, edit, or change any
*  of this code and then resell it, which would be copyright infringement.
*  This code can be modified for personal use only.
*
*  Comments, Questions? Contact the author at cody [at] wshost [dot] net
*/

class AES {
        // The number of 32-bit words comprising the plaintext and columns comrising the state matrix of an AES cipher.
        private static $Nb = 4;
        // The number of 32-bit words comprising the cipher key in this AES cipher.
        private $Nk;
        // The number of rounds in this AES cipher.
        private $Nr;

        // The S-Box substitution table.
        private 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
        );

        // The inverse S-Box substitution table.
        private static $invSBox = array(
                0x52, 0x09, 0x6a, 0xd5, 0x30, 0x36, 0xa5, 0x38,
                0xbf, 0x40, 0xa3, 0x9e, 0x81, 0xf3, 0xd7, 0xfb,
                0x7c, 0xe3, 0x39, 0x82, 0x9b, 0x2f, 0xff, 0x87,
                0x34, 0x8e, 0x43, 0x44, 0xc4, 0xde, 0xe9, 0xcb,
                0x54, 0x7b, 0x94, 0x32, 0xa6, 0xc2, 0x23, 0x3d,
                0xee, 0x4c, 0x95, 0x0b, 0x42, 0xfa, 0xc3, 0x4e,
                0x08, 0x2e, 0xa1, 0x66, 0x28, 0xd9, 0x24, 0xb2,
                0x76, 0x5b, 0xa2, 0x49, 0x6d, 0x8b, 0xd1, 0x25,
                0x72, 0xf8, 0xf6, 0x64, 0x86, 0x68, 0x98, 0x16,
                0xd4, 0xa4, 0x5c, 0xcc, 0x5d, 0x65, 0xb6, 0x92,
                0x6c, 0x70, 0x48, 0x50, 0xfd, 0xed, 0xb9, 0xda,
                0x5e, 0x15, 0x46, 0x57, 0xa7, 0x8d, 0x9d, 0x84,
                0x90, 0xd8, 0xab, 0x00, 0x8c, 0xbc, 0xd3, 0x0a,
                0xf7, 0xe4, 0x58, 0x05, 0xb8, 0xb3, 0x45, 0x06,
                0xd0, 0x2c, 0x1e, 0x8f, 0xca, 0x3f, 0x0f, 0x02,
                0xc1, 0xaf, 0xbd, 0x03, 0x01, 0x13, 0x8a, 0x6b,
                0x3a, 0x91, 0x11, 0x41, 0x4f, 0x67, 0xdc, 0xea,
                0x97, 0xf2, 0xcf, 0xce, 0xf0, 0xb4, 0xe6, 0x73,
                0x96, 0xac, 0x74, 0x22, 0xe7, 0xad, 0x35, 0x85,
                0xe2, 0xf9, 0x37, 0xe8, 0x1c, 0x75, 0xdf, 0x6e,
                0x47, 0xf1, 0x1a, 0x71, 0x1d, 0x29, 0xc5, 0x89,
                0x6f, 0xb7, 0x62, 0x0e, 0xaa, 0x18, 0xbe, 0x1b,
                0xfc, 0x56, 0x3e, 0x4b, 0xc6, 0xd2, 0x79, 0x20,
                0x9a, 0xdb, 0xc0, 0xfe, 0x78, 0xcd, 0x5a, 0xf4,
                0x1f, 0xdd, 0xa8, 0x33, 0x88, 0x07, 0xc7, 0x31,
                0xb1, 0x12, 0x10, 0x59, 0x27, 0x80, 0xec, 0x5f,
                0x60, 0x51, 0x7f, 0xa9, 0x19, 0xb5, 0x4a, 0x0d,
                0x2d, 0xe5, 0x7a, 0x9f, 0x93, 0xc9, 0x9c, 0xef,
                0xa0, 0xe0, 0x3b, 0x4d, 0xae, 0x2a, 0xf5, 0xb0,
                0xc8, 0xeb, 0xbb, 0x3c, 0x83, 0x53, 0x99, 0x61,
                0x17, 0x2b, 0x04, 0x7e, 0xba, 0x77, 0xd6, 0x26,
                0xe1, 0x69, 0x14, 0x63, 0x55, 0x21, 0x0c, 0x7d
        );

        // Log table based on 0xe5
        private static $ltable = array(
                0x00, 0xff, 0xc8, 0x08, 0x91, 0x10, 0xd0, 0x36,
                0x5a, 0x3e, 0xd8, 0x43, 0x99, 0x77, 0xfe, 0x18,
                0x23, 0x20, 0x07, 0x70, 0xa1, 0x6c, 0x0c, 0x7f,
                0x62, 0x8b, 0x40, 0x46, 0xc7, 0x4b, 0xe0, 0x0e,
                0xeb, 0x16, 0xe8, 0xad, 0xcf, 0xcd, 0x39, 0x53,
                0x6a, 0x27, 0x35, 0x93, 0xd4, 0x4e, 0x48, 0xc3,
                0x2b, 0x79, 0x54, 0x28, 0x09, 0x78, 0x0f, 0x21,
                0x90, 0x87, 0x14, 0x2a, 0xa9, 0x9c, 0xd6, 0x74,
                0xb4, 0x7c, 0xde, 0xed, 0xb1, 0x86, 0x76, 0xa4,
                0x98, 0xe2, 0x96, 0x8f, 0x02, 0x32, 0x1c, 0xc1,
                0x33, 0xee, 0xef, 0x81, 0xfd, 0x30, 0x5c, 0x13,
                0x9d, 0x29, 0x17, 0xc4, 0x11, 0x44, 0x8c, 0x80,
                0xf3, 0x73, 0x42, 0x1e, 0x1d, 0xb5, 0xf0, 0x12,
                0xd1, 0x5b, 0x41, 0xa2, 0xd7, 0x2c, 0xe9, 0xd5,
                0x59, 0xcb, 0x50, 0xa8, 0xdc, 0xfc, 0xf2, 0x56,
                0x72, 0xa6, 0x65, 0x2f, 0x9f, 0x9b, 0x3d, 0xba,
                0x7d, 0xc2, 0x45, 0x82, 0xa7, 0x57, 0xb6, 0xa3,
                0x7a, 0x75, 0x4f, 0xae, 0x3f, 0x37, 0x6d, 0x47,
                0x61, 0xbe, 0xab, 0xd3, 0x5f, 0xb0, 0x58, 0xaf,
                0xca, 0x5e, 0xfa, 0x85, 0xe4, 0x4d, 0x8a, 0x05,
                0xfb, 0x60, 0xb7, 0x7b, 0xb8, 0x26, 0x4a, 0x67,
                0xc6, 0x1a, 0xf8, 0x69, 0x25, 0xb3, 0xdb, 0xbd,
                0x66, 0xdd, 0xf1, 0xd2, 0xdf, 0x03, 0x8d, 0x34,
                0xd9, 0x92, 0x0d, 0x63, 0x55, 0xaa, 0x49, 0xec,
                0xbc, 0x95, 0x3c, 0x84, 0x0b, 0xf5, 0xe6, 0xe7,
                0xe5, 0xac, 0x7e, 0x6e, 0xb9, 0xf9, 0xda, 0x8e,
                0x9a, 0xc9, 0x24, 0xe1, 0x0a, 0x15, 0x6b, 0x3a,
                0xa0, 0x51, 0xf4, 0xea, 0xb2, 0x97, 0x9e, 0x5d,
                0x22, 0x88, 0x94, 0xce, 0x19, 0x01, 0x71, 0x4c,
                0xa5, 0xe3, 0xc5, 0x31, 0xbb, 0xcc, 0x1f, 0x2d,
                0x3b, 0x52, 0x6f, 0xf6, 0x2e, 0x89, 0xf7, 0xc0,
                0x68, 0x1b, 0x64, 0x04, 0x06, 0xbf, 0x83, 0x38
        );

        // Inverse log table
        private static $atable = array(
                0x01, 0xe5, 0x4c, 0xb5, 0xfb, 0x9f, 0xfc, 0x12,
                0x03, 0x34, 0xd4, 0xc4, 0x16, 0xba, 0x1f, 0x36,
                0x05, 0x5c, 0x67, 0x57, 0x3a, 0xd5, 0x21, 0x5a,
                0x0f, 0xe4, 0xa9, 0xf9, 0x4e, 0x64, 0x63, 0xee,
                0x11, 0x37, 0xe0, 0x10, 0xd2, 0xac, 0xa5, 0x29,
                0x33, 0x59, 0x3b, 0x30, 0x6d, 0xef, 0xf4, 0x7b,
                0x55, 0xeb, 0x4d, 0x50, 0xb7, 0x2a, 0x07, 0x8d,
                0xff, 0x26, 0xd7, 0xf0, 0xc2, 0x7e, 0x09, 0x8c,
                0x1a, 0x6a, 0x62, 0x0b, 0x5d, 0x82, 0x1b, 0x8f,
                0x2e, 0xbe, 0xa6, 0x1d, 0xe7, 0x9d, 0x2d, 0x8a,
                0x72, 0xd9, 0xf1, 0x27, 0x32, 0xbc, 0x77, 0x85,
                0x96, 0x70, 0x08, 0x69, 0x56, 0xdf, 0x99, 0x94,
                0xa1, 0x90, 0x18, 0xbb, 0xfa, 0x7a, 0xb0, 0xa7,
                0xf8, 0xab, 0x28, 0xd6, 0x15, 0x8e, 0xcb, 0xf2,
                0x13, 0xe6, 0x78, 0x61, 0x3f, 0x89, 0x46, 0x0d,
                0x35, 0x31, 0x88, 0xa3, 0x41, 0x80, 0xca, 0x17,
                0x5f, 0x53, 0x83, 0xfe, 0xc3, 0x9b, 0x45, 0x39,
                0xe1, 0xf5, 0x9e, 0x19, 0x5e, 0xb6, 0xcf, 0x4b,
                0x38, 0x04, 0xb9, 0x2b, 0xe2, 0xc1, 0x4a, 0xdd,
                0x48, 0x0c, 0xd0, 0x7d, 0x3d, 0x58, 0xde, 0x7c,
                0xd8, 0x14, 0x6b, 0x87, 0x47, 0xe8, 0x79, 0x84,
                0x73, 0x3c, 0xbd, 0x92, 0xc9, 0x23, 0x8b, 0x97,
                0x95, 0x44, 0xdc, 0xad, 0x40, 0x65, 0x86, 0xa2,
                0xa4, 0xcc, 0x7f, 0xec, 0xc0, 0xaf, 0x91, 0xfd,
                0xf7, 0x4f, 0x81, 0x2f, 0x5b, 0xea, 0xa8, 0x1c,
                0x02, 0xd1, 0x98, 0x71, 0xed, 0x25, 0xe3, 0x24,
                0x06, 0x68, 0xb3, 0x93, 0x2c, 0x6f, 0x3e, 0x6c,
                0x0a, 0xb8, 0xce, 0xae, 0x74, 0xb1, 0x42, 0xb4,
                0x1e, 0xd3, 0x49, 0xe9, 0x9c, 0xc8, 0xc6, 0xc7,
                0x22, 0x6e, 0xdb, 0x20, 0xbf, 0x43, 0x51, 0x52,
                0x66, 0xb2, 0x76, 0x60, 0xda, 0xc5, 0xf3, 0xf6,
                0xaa, 0xcd, 0x9a, 0xa0, 0x75, 0x54, 0x0e, 0x01
        );

        // The key schedule in this AES cipher.
        private $w;
        // The state matrix in this AES cipher with Nb columns and 4 rows
        private $s;
        // Determines the lenght of key z
        private $keyLength;


        /** constructs an AES cipher using a specific key.
        */
        public function __construct($z) {
               $this->Nk = strlen($z)/4;
               $this->Nr = $this->Nk + self::$Nb + 2;

               if ($this->Nk != 4 && $this->Nk != 6 && $this->Nk != 8)
                    throw new Exception("Key is " . ($this->Nk*32) . " bits long. *not* 128, 192, or 256.");

               $this->Nr = $this->Nk+self::$Nb+2;
               $this->w = array(); // Nb*(Nr+1) 32-bit words
               $this->s = array(array());  // 2-D array of Nb colums and 4 rows

               $this->KeyExpansion($z); // places expanded key in w
        }

        /** Encrypts an aribtrary length String.
        *   @params plaintext string
        *   @returns ciphertext string
        *   Whenever possible you should stream your plaintext through the
        *   encryptBlock() function directly, as the amount of time required
        *   to encrypt is linear to the size of the ciphertext.
        **/
        public function encrypt($x) {
                $t = ""; // 16-byte block
                $y = ""; // returned cipher text;

                // put a 16-byte block into t
                $xsize = strlen($x);
                for ($i=0; $i<$xsize; $i+=16) {
                        for ($j=0; $j<16; $j++) {
                                if (($i+$j)<$xsize) {
                                        $t[$j] = $x[$i+$j];
                                }
                                else
                                        $t[$j] = chr(0);
                        }

                        $y .= $this->encryptBlock($t);
                }
                return $y;
        }

        /** Decrypts an aribtrary length String.
        *   @params ciphertext string
        *   @returns plaintext string
        *   Whenever possible you should stream your ciphertext through the
        *   decryptBlock() function directly, as the amount of time required
        *   to decrypt is linear to the size of the ciphertext.
        **/
        public function decrypt($y) {
                $t = ""; // 16-byte block
                $x = ""; // returned plain text;

                // put a 16-byte block into t
                $ysize = strlen($y);
                for ($i=0; $i<$ysize; $i+=16) {
                        for ($j=0; $j<16; $j++) {
                                if (($i+$j)<$ysize)
                                        $t[$j] = $y[$i+$j];
                                else
                                        $t[$j] = chr(0);
                        }
                        $x .= $this->decryptBlock($t);
                }
                return $x;
        }

        /** Encrypts the 16-byte plain text.
        *   @params 16-byte plaintext string
        *   @returns 16-byte ciphertext string
        **/
        public function encryptBlock($x) {
                $y = ""; // 16-byte string

                // place input x into the initial state matrix in column order
                for ($i=0; $i<4*self::$Nb; $i++) {
                        // we want integerger division for the second index
                        $this->s[$i%4][($i-$i%self::$Nb)/self::$Nb] = ord($x[$i]);
                }

                // add round key
                $this->addRoundKey(0);

                for ($i=1; $i<$this->Nr; $i++) {
                        // substitute bytes
                        $this->subBytes();

                        // shift rows
                        $this->shiftRows();

                        // mix columns
                        $this->mixColumns();

                        // add round key
                        $this->addRoundKey($i);
                }

                // substitute bytes
                $this->subBytes();

                // shift rows
                $this->shiftRows();

                // add round key
                $this->addRoundKey($i);

                // place state matrix s into y in column order
                for ($i=0; $i<4*self::$Nb; $i++)
                       $y .= chr($this->s[$i%4][($i-$i%self::$Nb)/self::$Nb]);
                return $y;
        }

        /** Decrypts the 16-byte cipher text.
        *   @params 16-byte ciphertext string
        *   @returns 16-byte plaintext string
        **/
        public function decryptBlock($y) {
                $x = ""; // 16-byte string

                // place input y into the initial state matrix in column order
                for ($i=0; $i<4*self::$Nb; $i++)
                        $this->s[$i%4][($i-$i%self::$Nb)/self::$Nb] = ord($y[$i]);

                // add round key
                $this->addRoundKey($this->Nr);

                for ($i=$this->Nr-1; $i>0; $i--) {
                        // inverse shift rows
                        $this->invShiftRows();

                        // inverse sub bytes
                        $this->invSubBytes();

                        // add round key
                        $this->addRoundKey($i);

                        // inverse mix columns
                        $this->invMixColumns();
                }

                // inverse shift rows
                $this->invShiftRows();

                // inverse sub bytes
                $this->invSubBytes();

                // add round key
                $this->addRoundKey($i);

                // place state matrix s into x in column order
                for ($i=0; $i<4*self::$Nb; $i++) {
                       // Used to remove filled null characters.
                       $x .= ($this->s[$i%4][($i-$i%self::$Nb)/self::$Nb] == chr(0) ? "" : chr($this->s[$i%4][($i-$i%self::$Nb)/self::$Nb]));
                }

                return $x;
        }

        public function __destruct() {
                unset($this->w);
                unset($this->s);
        }

        /** makes a big key out of a small one
        *   @returns void
        **/
        private function KeyExpansion($z) {
                // Rcon is the round constant
                static $Rcon = array(
                        0x00000000,
                        0x01000000,
                        0x02000000,
                        0x04000000,
                        0x08000000,
                        0x10000000,
                        0x20000000,
                        0x40000000,
                        0x80000000,
                        0x1b000000,
                        0x36000000,
                        0x6c000000,
                        0xd8000000,
                        0xab000000,
                        0x4d000000,
                        0x9a000000,
                        0x2f000000
                );

                $temp = 0; // temporary 32-bit word

                // the first Nk words of w are the cipher key z
                for ($i=0; $i<$this->Nk; $i++) {
                        $this->w[$i] = 0;
                        // fill an entire word of expanded key w
                        // by pushing 4 bytes into the w[i] word
                        $this->w[$i] = ord($z[4*$i]); // add a byte in
                        $this->w[$i] <<= 8; // make room for the next byte
                        $this->w[$i] += ord($z[4*$i+1]);
                        $this->w[$i] <<= 8;
                        $this->w[$i] += ord($z[4*$i+2]);
                        $this->w[$i] <<= 8;
                        $this->w[$i] += ord($z[4*$i+3]);
                }


                for (; $i<self::$Nb*($this->Nr+1); $i++) {
                        $temp = $this->w[$i-1];

                        if ($i%$this->Nk == 0)
                                $temp = $this->subWord($this->rotWord($temp)) ^ $Rcon[$i/$this->Nk];
                        else if ($this->Nk > 6 && $i%$this->Nk == 4)
                                $temp = $this->subWord($temp);

                        $this->w[$i] = $this->w[$i-$this->Nk] ^ $temp;

               	       self::make32BitWord($this->w[$i]);
                }
        }

        /** adds the key schedule for a round to a state matrix.
        *   @returns void
        **/
        private function addRoundKey($round) {
                $temp = "";

                for ($i=0; $i<4; $i++) {
                        for ($j=0; $j<self::$Nb; $j++) {
                                // place the i-th byte of the j-th word from expanded key w into temp
                                $temp = $this->w[$round*self::$Nb+$j] >> (3-$i)*8;
                                // Cast temp from a 32-bit word into an 8-bit byte.
                                $temp %= 256;
                                // Can't do unsigned shifts, so we need to make this temp positive
                                $temp = ($temp < 0 ? (256 + $temp) : $temp);

                                $this->s[$i][$j] ^= $temp; // xor temp with the byte at location (i,j) of the state
                        }
                }
        }

        /** unmixes each column of a state matrix.
        *   @returns void
        **/
        private function invMixColumns() {
                $s0 = $s1 = $s2 = $s3= '';

                // There are Nb columns
                for ($i=0; $i<self::$Nb; $i++) {
                        $s0 = $this->s[0][$i]; $s1 = $this->s[1][$i]; $s2 = $this->s[2][$i]; $s3 = $this->s[3][$i];

                        $this->s[0][$i] = $this->mult(0x0e, $s0) ^ $this->mult(0x0b, $s1) ^ $this->mult(0x0d, $s2) ^ $this->mult(0x09, $s3);
                        $this->s[1][$i] = $this->mult(0x09, $s0) ^ $this->mult(0x0e, $s1) ^ $this->mult(0x0b, $s2) ^ $this->mult(0x0d, $s3);
                        $this->s[2][$i] = $this->mult(0x0d, $s0) ^ $this->mult(0x09, $s1) ^ $this->mult(0x0e, $s2) ^ $this->mult(0x0b, $s3);
                        $this->s[3][$i] = $this->mult(0x0b, $s0) ^ $this->mult(0x0d, $s1) ^ $this->mult(0x09, $s2) ^ $this->mult(0x0e, $s3);

                }
        }

        /** applies an inverse cyclic shift to the last 3 rows of a state matrix.
        *   @returns void
        **/
        private function invShiftRows() {
                $temp = "";
                for ($i=1; $i<4; $i++) {
                        for ($j=0; $j<self::$Nb; $j++)
                                $temp[($i+$j)%self::$Nb] = $this->s[$i][$j];
                        for ($j=0; $j<self::$Nb; $j++)
                                $this->s[$i][$j] = $temp[$j];
                }
        }

        /** applies inverse S-Box substitution to each byte of a state matrix.
        *   @returns void
        **/
        private function invSubBytes() {
                for ($i=0; $i<4; $i++)
                        for ($j=0; $j<self::$Nb; $j++)
                                $this->s[$i][$j] = self::$invSBox[$this->s[$i][$j]];
        }

        /** mixes each column of a state matrix.
        *   @returns void
        **/
        private function mixColumns() {
                $s0 = $s1 = $s2 = $s3= '';

                // There are Nb columns
                for ($i=0; $i<self::$Nb; $i++) {
                        $s0 = $this->s[0][$i]; $s1 = $this->s[1][$i]; $s2 = $this->s[2][$i]; $s3 = $this->s[3][$i];

                        $this->s[0][$i] = $this->mult(0x02, $s0) ^ $this->mult(0x03, $s1) ^ $this->mult(0x01, $s2) ^ $this->mult(0x01, $s3);
                        $this->s[1][$i] = $this->mult(0x01, $s0) ^ $this->mult(0x02, $s1) ^ $this->mult(0x03, $s2) ^ $this->mult(0x01, $s3);
                        $this->s[2][$i] = $this->mult(0x01, $s0) ^ $this->mult(0x01, $s1) ^ $this->mult(0x02, $s2) ^ $this->mult(0x03, $s3);
                        $this->s[3][$i] = $this->mult(0x03, $s0) ^ $this->mult(0x01, $s1) ^ $this->mult(0x01, $s2) ^ $this->mult(0x02, $s3);
                }
        }

        /** applies a cyclic shift to the last 3 rows of a state matrix.
        *   @returns void
        **/
        private function shiftRows() {
                $temp = "";
                for ($i=1; $i<4; $i++) {
                        for ($j=0; $j<self::$Nb; $j++)
                                $temp[$j] = $this->s[$i][($j+$i)%self::$Nb];
                        for ($j=0; $j<self::$Nb; $j++)
                                $this->s[$i][$j] = $temp[$j];
                }
        }
        /** applies S-Box substitution to each byte of a state matrix.
        *   @returns void
        **/
        private function subBytes() {

                for ($i=0; $i<4; $i++) {
                        for ($j=0; $j<self::$Nb; $j++)
                                $this->s[$i][$j] = self::$sBox[$this->s[$i][$j]];
                }
        }

        /** multiplies two polynomials a(x), b(x) in GF(2^8) modulo the irreducible polynomial m(x) = x^8+x^4+x^3+x+1
        *   @returns 8-bit value
        **/
        private static function mult($a, $b) {
                $sum = self::$ltable[$a] + self::$ltable[$b];
                $sum %= 255;
                // Get the antilog
                $sum = self::$atable[$sum];
                return ($a == 0 ? 0 : ($b == 0 ? 0 : $sum));
        }

        /** applies a cyclic permutation to a 4-byte word.
        *   @returns 32-bit int
        **/
        private static function rotWord($w) {
                $temp = $w >> 24; // put the first 8-bits into temp
                $w <<= 8; // make room for temp to fill the lower end of the word
                self::make32BitWord($w);
                // Can't do unsigned shifts, so we need to make this temp positive
                $temp = ($temp < 0 ? (256 + $temp) : $temp);
                $w += $temp;

                return $w;
        }

        /** applies S-box substitution to each byte of a 4-byte word.
        *   @returns 32-bit int
        **/
        private static function subWord($w) {
                $temp = 0;
                // loop through 4 bytes of a word
                for ($i=0; $i<4; $i++) {
                        $temp = $w >> 24; // put the first 8-bits into temp
                        // Can't do unsigned shifts, so we need to make this temp positive
                        $temp = ($temp < 0 ? (256 + $temp) : $temp);
                        $w <<= 8; // make room for the substituted byte in w;
                        self::make32BitWord($w);
                        $w += self::$sBox[$temp]; // add the substituted byte back
                }

                self::make32BitWord($w);

                return $w;
        }

        /** reduces a 64-bit word to a 32-bit word
        *   @returns void
        **/
        private static function make32BitWord(&$w) {
                // Reduce this 64-bit word to 32-bits on 64-bit machines
	       $w &= 0x00000000FFFFFFFF;
        }
}
?>