<?php
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
/*  AES implementation in PHP                                                                     */
/*    (c) Chris Veness 2005-2011 www.movable-type.co.uk/scripts                                   */
/*    Right of free use is granted for all commercial or non-commercial use providing this        */
/*    copyright notice is retainded. No warranty of any form is offered.                          */
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
  
class Aes {
  
  /**
   * 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;
  }
  
  
  private 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;
  }
  
  private 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;
  }
  
  private 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 
  }
  
  private 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;
  }
  
  private 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;
  }
  
  private 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;
  }
  
  // sBox is pre-computed multiplicative inverse in GF(2^8) used in subBytes and keyExpansion [§5.1.1]
  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);
  
  // rCon is Round Constant used for the Key Expansion [1st col is 2^(r-1) in GF(2^8)] [§5.2]
  private 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) ); 

} 
 
/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */
?>