<?php
namespace PhpAes;

/**
 *  AES cipher
 *
 */
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 = array(); // Nb*(Nr+1) 32-bit words
    // The state matrix in this AES cipher with Nb columns and 4 rows
    private $s = array(array());
    // The block cipher mode of operation
    private $mode;
    // The initialization vector used in advanced cipher modes
    private $iv;


    /**
     * Constructs an AES cipher using a specific key.
     *
     * @throws LengthException if the initialization vector or key is not the
     *  appropriate length.
     */
    public function __construct($z, $mode = 'ECB', $iv = null)
    {
        $this->mode = strtoupper($mode);
        $this->iv = $iv;
        $this->Nk = strlen($z)/4;
        $this->Nr = $this->Nk + self::$Nb + 2;

        if ($this->mode != 'ECB' && strlen($this->iv) != 16) {
            throw new \LengthException(
                'The initialization vector must be 128 bits (or 16 characters) long.'
            );
        }

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

        $this->Nr = $this->Nk+self::$Nb+2;

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

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

    /**
     * Encrypts an aribtrary length String.
     * @params plaintext string
     * @returns ciphertext string
     */
    public function encrypt($x)
    {
        $t = ''; // 16-byte block to hold the temporary input of the cipher
        $y = ''; // returned cipher text;
        $y_block = $this->iv; // 16-byte block to hold the temporary output of the cipher
        $xsize = strlen($x);

        switch ($this->mode) {
            case 'ECB':
                // put a 16-byte block into t, ecnrypt it and add it to the result
                for ($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_block = $this->encryptBlock($t);
                    $y .= $y_block;
                }
                break;
            case 'CBC':
                // put a 16-byte block into t, ecnrypt it and add it to the result
                for ($i = 0; $i < $xsize; $i += 16) {
                    for ($j=0; $j<16; $j++) {
                        // XOR this block of plaintext with the initialization vector
                        $t[$j] = chr(ord(($i+$j)<$xsize ? $x[$i+$j] : chr(0)) ^ ord($y_block[$j]));
                    }

                    $y_block = $this->encryptBlock($t);
                    $y .= $y_block;
                }
                break;
            case 'CFB':
                for ($i = 0; $i < $xsize; $i += 16) {
                    // Encrypt the initialization vector/cipher output then XOR with the plaintext
                    $y_block = $this->encryptBlock($y_block);

                    for ($j = 0; $j < 16; $j++) {
                        // XOR the cipher output with the plaintext.
                        $y_block[$j] = chr(ord(($i+$j)<$xsize ? $x[$i+$j] : chr(0)) ^ ord($y_block[$j]));
                    }

                    $y .= $y_block;
                }

                break;
            case 'OFB':
                for ($i = 0; $i < $xsize; $i += 16) {
                    // Encrypt the initialization vector/cipher output then XOR with the plaintext
                    $t = $this->encryptBlock($y_block);

                    for ($j = 0; $j < 16; $j++) {
                        // XOR the cipher output with the plaintext.
                        $y_block[$j] = chr(ord(($i+$j)<$xsize ? $x[$i+$j] : chr(0)) ^ ord($t[$j]));
                    }

                    $y .= $y_block;
                    $y_block = $t;
                }
                break;
        }
        return $y;
    }

    /**
     * Decrypts an aribtrary length String.
     * @params ciphertext string
     * @returns plaintext string
     */
    public function decrypt($y)
    {
        $t = array(); // 16-byte block
        $x = ''; // returned plain text;
        $y_block = $this->iv;
        $x_block = '';

        // put a 16-byte block into t
        $ysize = strlen($y);

        switch ($this->mode) {
            case 'ECB':
                for ($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_block = $this->decryptBlock($t);
                    $x .= $x_block;
                }
                break;
            case 'CBC':
                for ($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_block = $this->decryptBlock($t);

                    // XOR the iv/previous cipher block with this decrypted cipher block
                    for ($j = 0; $j < 16; $j++) {
                        $x_block[$j] = chr(ord($x_block[$j]) ^ ord($y_block[$j]));
                    }

                    $y_block = $t;
                    $x .= $x_block;
                }
                break;
            case 'CFB':
                for ($i = 0; $i < $ysize; $i += 16) {
                    // Encrypt the initialization vector/cipher output then XOR with the ciphertext
                    $x_block = $this->encryptBlock($y_block);

                    for ($j = 0; $j < 16; $j++) {
                        // XOR the cipher output with the ciphertext.
                        $x_block[$j] = chr(ord(($i+$j)<$ysize ? $y[$i+$j] : chr(0)) ^ ord($x_block[$j]));
                        $y_block[$j] = $y[$i+$j];
                    }

                    $x .= $x_block;
                }
                break;
            case 'OFB':
                $x = $this->encrypt($y);
                break;
        }
        return rtrim($x, chr(0)); // Remove any buffer residue on return.
    }

    /**
     * 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.
            $x .= chr($this->s[$i%4][($i-$i%self::$Nb)/self::$Nb]);
        }

        return $x;
    }

    /**
     * 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/$this->Nk];
            } elseif ($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()
    {
        $temp = array();
        for ($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()
    {
        $temp = array();
        for ($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 : 0;
        $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 : 0;
            $w <<= 8; // make room for the substituted byte in w;
            self::make32BitWord($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;
    }
}