/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */

/*
 * AES Cipher function: use 'key' to encrypt 'input' with Rijndael algorithm
 *
 *   takes   byte-array 'input' (16 bytes)
 *           byte-array 'key' (16/24/32 bytes)
             2D byte-array key schedule 'w' (Nr+1 x Nb bytes)
 *   returns byte-array encrypted value (16 bytes)
 *
 *  Chris Veness, http://www.movable-type.co.uk/scripts/AES.html
 */
function Cipher(input, key, w) {
  var Nk = key.length/4  // key length (in words)
  var Nr = Nk + 6;       // no of rounds
  var Nb = 4;            // block size: no of columns in state (fixed at 4 for AES)

  var state = [[],[],[],[]];  // initialise 4xNb byte-array 'state' with input
  for (var i=0; i<4*Nb; i++) state[i%4][Math.floor(i/4)] = input[i];

  state = AddRoundKey(state, w, 0, Nb);

  for (var round=1; round<Nr; round++) {
    state = SubBytes(state, Nb);
    state = ShiftRows(state, Nb);
    state = MixColumns(state, Nb);
    state = AddRoundKey(state, w, round, Nb);
  }

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

  var output = new Array(4*Nb);  // convert to 1-d array before returning
  for (var i=0; i<4*Nb; i++) output[i] = state[i%4][Math.floor(i/4)];
  return output;
}


function SubBytes(s, Nb) {    // apply SBox to state S [§5.1.1]
  for (var r=0; r<4; r++) {
    for (var c=0; c<Nb; c++) s[r][c] = Sbox[s[r][c]];
  }
  return s;
}


function ShiftRows(s, Nb) {    // shift row r of state S left by r bytes [§5.1.2]
  var t = new Array(4);
  for (var r=1; r<4; r++) {
    for (var c=0; c<4; c++) t[c] = s[r][(c+r)%Nb];  // shift into temp copy
    for (var 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: see
  return s;  // fp.gladman.plus.com/cryptography_technology/rijndael/aes.spec.311.pdf 
}


function MixColumns(s, Nb) {   // combine bytes of each col of state S [§5.1.3]
  for (var c=0; c<4; c++) {
    var a = new Array(4);  // 'a' is a copy of the current column from 's'
    var b = new Array(4);  // 'b' is a{02} in GF(2^8)
    for (var 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;
}


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


function KeyExpansion(key) {  // generate Key Schedule (byte-array Nr+1 x Nb) from Key [§5.2]
  var Nk = key.length/4  // key length (in words)
  var Nr = Nk + 6;       // no of rounds
  var Nb = 4;            // block size: no of columns in state (fixed at 4 for AES)

  var w = new Array(Nb*(Nr+1));
  var temp = new Array(4);

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

  for (var i=Nk; i<(Nb*(Nr+1)); i++) {
    w[i] = new Array(4);
    for (var t=0; t<4; t++) temp[t] = w[i-1][t];
    if (i % Nk == 0) {
      temp = SubWord(RotWord(temp));
      for (var t=0; t<4; t++) temp[t] ^= Rcon[i/Nk][t];
    } else if (Nk > 6 && i%Nk == 4) {
      temp = SubWord(temp);
    }
    for (var t=0; t<4; t++) w[i][t] = w[i-Nk][t] ^ temp[t];
  }

  return w;
}

function SubWord(w) {    // apply SBox to 4-byte word w
  for (var i=0; i<4; i++) w[i] = Sbox[w[i]];
  return w;
}

function RotWord(w) {    // rotate 4-byte word w left by one byte
  w[4] = w[0];
  for (var i=0; i<4; i++) w[i] = w[i+1];
  return w;
}


// Sbox is pre-computed multiplicative inverse in GF(2^8) used in SubBytes and KeyExpansion
var Sbox =  [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)]
var Rcon = [ [0x00, 0x00, 0x00, 0x00],
             [0x01, 0x00, 0x00, 0x00],
             [0x02, 0x00, 0x00, 0x00],
             [0x04, 0x00, 0x00, 0x00],
             [0x08, 0x00, 0x00, 0x00],
             [0x10, 0x00, 0x00, 0x00],
             [0x20, 0x00, 0x00, 0x00],
             [0x40, 0x00, 0x00, 0x00],
             [0x80, 0x00, 0x00, 0x00],
             [0x1b, 0x00, 0x00, 0x00],
             [0x36, 0x00, 0x00, 0x00] ]; 


/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */

/* 
 * Use AES to encrypt 'plaintext' with 'password' using 128-bit key, in 'Counter' mode of operation
 *                           - see http://csrc.nist.gov/publications/nistpubs/800-38a/sp800-38a.pdf
 *   for each block
 *   - outputblock = cipher(counter, key)
 *   - cipherblock = plaintext xor outputblock
 */
function AESEncryptCtr128(plaintext, password) {
  // ensure plaintext only contains 8-bit characters: use 'escape' to convert anything outside 
  // ISO-8859-1, but keep spaces as spaces not '%20' to restrict bloat
  plaintext = escape(plaintext).replace(/%20/g,' ');

  // for this example script, generate the key by applying Cipher to 1st 16 chars of password; for 
  // real-world applications, a more secure approach would be to hash the password e.g. with SHA-1
  var pwBytes = new Array(16);
  for (var i=0; i<16; i++) pwBytes[i] = password.charCodeAt(i);
  var pwKeySchedule = KeyExpansion([0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1]);
  var key = Cipher(pwBytes, pwBytes, pwKeySchedule);

  // initialise counter block (NIST SP800-38A §B.2)
  var counterBlock = new Array(16);
  var nonce = (new Date()).getTime();  // milliseconds since 1-Jan-1970
  for (var i=0; i<8; i++) counterBlock[i] = (nonce >>> i*8) & 0xff;

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

  var blockCount = Math.ceil(plaintext.length/16);
  var ciphertext = new Array(blockCount);  // ciphertext as array of strings
  
  for (var b=0; b<blockCount; b++) {
    for (var c=0; c<8; c++) counterBlock[15-c] = (b >>> c*8) & 0xff;  // set counter in counter block

    var cipherCntr = Cipher(counterBlock, key, keySchedule);  // -- encrypt counter block --
    
    // calculate length of final block:
    var blockLength = b<blockCount-1 ? 16 : (plaintext.length-1)%16+1;

    var ct = '';
    for (var i=0; i<blockLength; i++) {  // -- xor plaintext with ciphered counter byte-by-byte --
      var plaintextByte = plaintext.charCodeAt(b*16+i);
      var cipherByte = plaintextByte ^ cipherCntr[i];
      ct += String.fromCharCode(cipherByte);
    }

    ciphertext[b] = escCtrlChars(ct);  // escape troublesome characters in ciphertext
  }

  // convert the nonce to a string to go on the front of the ciphertext
  var ctrTxt = '';
  for (var i=0; i<8; i++) ctrTxt += String.fromCharCode(counterBlock[i]);
  ctrTxt = escCtrlChars(ctrTxt);

  // use '+' to separate blocks, since encrypted blocks are of variable size after escaping ctrl chars
  // use Array.join to concatenate arrays of strings, as repeated string concatenation would be slow
  return ctrTxt + '+' + ciphertext.join('+');
}


/* 
 * Use AES to decrypt 'ciphertext' with 'password' using 128-bit key, in Counter mode of operation
 *
 *   for each block
 *   - outputblock = cipher(counter, key)
 *   - cipherblock = plaintext xor outputblock
 */
function AESDecryptCtr128(ciphertext, password) {

  var pwBytes = new Array(16);
  for (var i=0; i<16; i++) pwBytes[i] = password.charCodeAt(i);
  var pwKeySchedule = KeyExpansion([0,1,0,1,0,1,0,1,0,1,0,1,0,1,0,1]);
  var key = Cipher(pwBytes, pwBytes, pwKeySchedule);

  var keySchedule = KeyExpansion(key);

  ciphertext = ciphertext.split('+');  // split ciphertext into array of block-length strings 

  // recover nonce from 1st element of ciphertext
  var counterBlock = new Array(16);
  var ctrTxt = unescCtrlChars(ciphertext[0]);
  for (var i=0; i<8; i++) counterBlock[i] = ctrTxt.charCodeAt(i);

  var plaintext = new Array(ciphertext.length-1);

  for (var b=1; b<ciphertext.length; b++) {
    for (var c=0; c<8; c++) counterBlock[15-c] = ((b-1) >>> c*8) & 0xff;  // set counter in counter block

    var cipherCntr = Cipher(counterBlock, key, keySchedule);  // encrypt counter block

    ciphertext[b] = unescCtrlChars(ciphertext[b]);

    var pt = '';
    for (var i=0; i<ciphertext[b].length; i++) {
      var ciphertextByte = ciphertext[b].charCodeAt(i);
      var plaintextByte = ciphertextByte ^ cipherCntr[i];
      pt += String.fromCharCode(plaintextByte);
    }

    plaintext[b] = pt;
  }

  return unescape(plaintext.join(''));
}


function escCtrlChars(str) {  // escape control chars which might cause problems handling ciphertext
  return str.replace(/[\0\n\v\f\r\xa0+!]/g, function(c) { return '!' + c.charCodeAt(0) + '!'; });
}  // \xa0 to cater for bug in Firefox; include '+' to leave it free for use as a block marker

function unescCtrlChars(str) {  // unescape potentially problematic control characters
  return str.replace(/!\d\d?\d?!/g, function(c) { return String.fromCharCode(c.slice(1,-1)); });
}

function byteArrayToHexStr(b) {  // convert byte array to hex string for displaying test vectors
  var s = '';
  for (var i=0; i<b.length; i++) s += b[i].toString(16) + ' ';
  return s;
}

/* - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -  */