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/* rijndael.js      Rijndael Reference Implementation\r
\r
    This is a modified version of the software described below,\r
    produced in September 2003 by John Walker for use in the\r
    JavsScrypt browser-based encryption package.  The principal\r
    changes are replacing the original getRandomBytes function with\r
    one which calls our pseudorandom generator (which must\r
    be instantiated and seeded before the first call on getRandomBytes),\r
    and changing keySizeInBits to 256.  Some code not required by the\r
    JavsScrypt application has been commented out.  Please see\r
    http://www.fourmilab.ch/javascrypt/ for further information on\r
    JavaScrypt.\r
    \r
    The following is the original copyright and application\r
    information.\r
\r
   Copyright (c) 2001 Fritz Schneider\r
 \r
 This software is provided as-is, without express or implied warranty.  \r
 Permission to use, copy, modify, distribute or sell this software, with or\r
 without fee, for any purpose and by any individual or organization, is hereby\r
 granted, provided that the above copyright notice and this paragraph appear \r
 in all copies. Distribution as a part of an application or binary must\r
 include the above copyright notice in the documentation and/or other materials\r
 provided with the application or distribution.\r
\r
   As the above disclaimer notes, you are free to use this code however you\r
   want. However, I would request that you send me an email \r
   (fritz /at/ cs /dot/ ucsd /dot/ edu) to say hi if you find this code useful\r
   or instructional. Seeing that people are using the code acts as \r
   encouragement for me to continue development. If you *really* want to thank\r
   me you can buy the book I wrote with Thomas Powell, _JavaScript:\r
   _The_Complete_Reference_ :)\r
\r
   This code is an UNOPTIMIZED REFERENCE implementation of Rijndael. \r
   If there is sufficient interest I can write an optimized (word-based, \r
   table-driven) version, although you might want to consider using a \r
   compiled language if speed is critical to your application. As it stands,\r
   one run of the monte carlo test (10,000 encryptions) can take up to \r
   several minutes, depending upon your processor. You shouldn't expect more\r
   than a few kilobytes per second in throughput.\r
\r
   Also note that there is very little error checking in these functions. \r
   Doing proper error checking is always a good idea, but the ideal \r
   implementation (using the instanceof operator and exceptions) requires\r
   IE5+/NS6+, and I've chosen to implement this code so that it is compatible\r
   with IE4/NS4. \r
\r
   And finally, because JavaScript doesn't have an explicit byte/char data \r
   type (although JavaScript 2.0 most likely will), when I refer to "byte" \r
   in this code I generally mean "32 bit integer with value in the interval \r
   [0,255]" which I treat as a byte.\r
\r
   See http://www-cse.ucsd.edu/~fritz/rijndael.html for more documentation\r
   of the (very simple) API provided by this code.\r
\r
                                               Fritz Schneider\r
                                               fritz at cs.ucsd.edu\r
 \r
*/\r
\r
\r
// Rijndael parameters --  Valid values are 128, 192, or 256\r
\r
var keySizeInBits = 256;\r
var blockSizeInBits = 128;\r
\r
//\r
// Note: in the following code the two dimensional arrays are indexed as\r
//       you would probably expect, as array[row][column]. The state arrays\r
//       are 2d arrays of the form state[4][Nb].\r
\r
\r
// The number of rounds for the cipher, indexed by [Nk][Nb]\r
var roundsArray = [ ,,,,[,,,,10,, 12,, 14],, \r
                        [,,,,12,, 12,, 14],, \r
                        [,,,,14,, 14,, 14] ];\r
\r
// The number of bytes to shift by in shiftRow, indexed by [Nb][row]\r
var shiftOffsets = [ ,,,,[,1, 2, 3],,[,1, 2, 3],,[,1, 3, 4] ];\r
\r
// The round constants used in subkey expansion\r
var Rcon = [ \r
0x01, 0x02, 0x04, 0x08, 0x10, 0x20, \r
0x40, 0x80, 0x1b, 0x36, 0x6c, 0xd8, \r
0xab, 0x4d, 0x9a, 0x2f, 0x5e, 0xbc, \r
0x63, 0xc6, 0x97, 0x35, 0x6a, 0xd4, \r
0xb3, 0x7d, 0xfa, 0xef, 0xc5, 0x91 ];\r
\r
// Precomputed lookup table for the SBox\r
var SBox = [\r
 99, 124, 119, 123, 242, 107, 111, 197,  48,   1, 103,  43, 254, 215, 171, \r
118, 202, 130, 201, 125, 250,  89,  71, 240, 173, 212, 162, 175, 156, 164, \r
114, 192, 183, 253, 147,  38,  54,  63, 247, 204,  52, 165, 229, 241, 113, \r
216,  49,  21,   4, 199,  35, 195,  24, 150,   5, 154,   7,  18, 128, 226, \r
235,  39, 178, 117,   9, 131,  44,  26,  27, 110,  90, 160,  82,  59, 214, \r
179,  41, 227,  47, 132,  83, 209,   0, 237,  32, 252, 177,  91, 106, 203, \r
190,  57,  74,  76,  88, 207, 208, 239, 170, 251,  67,  77,  51, 133,  69, \r
249,   2, 127,  80,  60, 159, 168,  81, 163,  64, 143, 146, 157,  56, 245, \r
188, 182, 218,  33,  16, 255, 243, 210, 205,  12,  19, 236,  95, 151,  68,  \r
23,  196, 167, 126,  61, 100,  93,  25, 115,  96, 129,  79, 220,  34,  42, \r
144, 136,  70, 238, 184,  20, 222,  94,  11, 219, 224,  50,  58,  10,  73,\r
  6,  36,  92, 194, 211, 172,  98, 145, 149, 228, 121, 231, 200,  55, 109, \r
141, 213,  78, 169, 108,  86, 244, 234, 101, 122, 174,   8, 186, 120,  37,  \r
 46,  28, 166, 180, 198, 232, 221, 116,  31,  75, 189, 139, 138, 112,  62, \r
181, 102,  72,   3, 246,  14,  97,  53,  87, 185, 134, 193,  29, 158, 225,\r
248, 152,  17, 105, 217, 142, 148, 155,  30, 135, 233, 206,  85,  40, 223,\r
140, 161, 137,  13, 191, 230,  66, 104,  65, 153,  45,  15, 176,  84, 187,  \r
 22 ];\r
\r
// Precomputed lookup table for the inverse SBox\r
var SBoxInverse = [\r
 82,   9, 106, 213,  48,  54, 165,  56, 191,  64, 163, 158, 129, 243, 215, \r
251, 124, 227,  57, 130, 155,  47, 255, 135,  52, 142,  67,  68, 196, 222, \r
233, 203,  84, 123, 148,  50, 166, 194,  35,  61, 238,  76, 149,  11,  66, \r
250, 195,  78,   8,  46, 161, 102,  40, 217,  36, 178, 118,  91, 162,  73, \r
109, 139, 209,  37, 114, 248, 246, 100, 134, 104, 152,  22, 212, 164,  92, \r
204,  93, 101, 182, 146, 108, 112,  72,  80, 253, 237, 185, 218,  94,  21,  \r
 70,  87, 167, 141, 157, 132, 144, 216, 171,   0, 140, 188, 211,  10, 247, \r
228,  88,   5, 184, 179,  69,   6, 208,  44,  30, 143, 202,  63,  15,   2, \r
193, 175, 189,   3,   1,  19, 138, 107,  58, 145,  17,  65,  79, 103, 220, \r
234, 151, 242, 207, 206, 240, 180, 230, 115, 150, 172, 116,  34, 231, 173,\r
 53, 133, 226, 249,  55, 232,  28, 117, 223, 110,  71, 241,  26, 113,  29, \r
 41, 197, 137, 111, 183,  98,  14, 170,  24, 190,  27, 252,  86,  62,  75, \r
198, 210, 121,  32, 154, 219, 192, 254, 120, 205,  90, 244,  31, 221, 168,\r
 51, 136,   7, 199,  49, 177,  18,  16,  89,  39, 128, 236,  95,  96,  81,\r
127, 169,  25, 181,  74,  13,  45, 229, 122, 159, 147, 201, 156, 239, 160,\r
224,  59,  77, 174,  42, 245, 176, 200, 235, 187,  60, 131,  83, 153,  97, \r
 23,  43,   4, 126, 186, 119, 214,  38, 225, 105,  20,  99,  85,  33,  12,\r
125 ];\r
\r
// This method circularly shifts the array left by the number of elements\r
// given in its parameter. It returns the resulting array and is used for \r
// the ShiftRow step. Note that shift() and push() could be used for a more \r
// elegant solution, but they require IE5.5+, so I chose to do it manually. \r
\r
function cyclicShiftLeft(theArray, positions) {\r
  var temp = theArray.slice(0, positions);\r
  theArray = theArray.slice(positions).concat(temp);\r
  return theArray;\r
}\r
\r
// Cipher parameters ... do not change these\r
var Nk = keySizeInBits / 32;                   \r
var Nb = blockSizeInBits / 32;\r
var Nr = roundsArray[Nk][Nb];\r
\r
// Multiplies the element "poly" of GF(2^8) by x. See the Rijndael spec.\r
\r
function xtime(poly) {\r
  poly <<= 1;\r
  return ((poly & 0x100) ? (poly ^ 0x11B) : (poly));\r
}\r
\r
// Multiplies the two elements of GF(2^8) together and returns the result.\r
// See the Rijndael spec, but should be straightforward: for each power of\r
// the indeterminant that has a 1 coefficient in x, add y times that power\r
// to the result. x and y should be bytes representing elements of GF(2^8)\r
\r
function mult_GF256(x, y) {\r
  var bit, result = 0;\r
  \r
  for (bit = 1; bit < 256; bit *= 2, y = xtime(y)) {\r
    if (x & bit) \r
      result ^= y;\r
  }\r
  return result;\r
}\r
\r
// Performs the substitution step of the cipher.  State is the 2d array of\r
// state information (see spec) and direction is string indicating whether\r
// we are performing the forward substitution ("encrypt") or inverse \r
// substitution (anything else)\r
\r
function byteSub(state, direction) {\r
  var S;\r
  if (direction == "encrypt")           // Point S to the SBox we're using\r
    S = SBox;\r
  else\r
    S = SBoxInverse;\r
  for (var i = 0; i < 4; i++)           // Substitute for every byte in state\r
    for (var j = 0; j < Nb; j++)\r
       state[i][j] = S[state[i][j]];\r
}\r
\r
// Performs the row shifting step of the cipher.\r
\r
function shiftRow(state, direction) {\r
  for (var i=1; i<4; i++)               // Row 0 never shifts\r
    if (direction == "encrypt")\r
       state[i] = cyclicShiftLeft(state[i], shiftOffsets[Nb][i]);\r
    else\r
       state[i] = cyclicShiftLeft(state[i], Nb - shiftOffsets[Nb][i]);\r
\r
}\r
\r
// Performs the column mixing step of the cipher. Most of these steps can\r
// be combined into table lookups on 32bit values (at least for encryption)\r
// to greatly increase the speed. \r
\r
function mixColumn(state, direction) {\r
  var b = [];                            // Result of matrix multiplications\r
  for (var j = 0; j < Nb; j++) {         // Go through each column...\r
    for (var i = 0; i < 4; i++) {        // and for each row in the column...\r
      if (direction == "encrypt")\r
        b[i] = mult_GF256(state[i][j], 2) ^          // perform mixing\r
               mult_GF256(state[(i+1)%4][j], 3) ^ \r
               state[(i+2)%4][j] ^ \r
               state[(i+3)%4][j];\r
      else \r
        b[i] = mult_GF256(state[i][j], 0xE) ^ \r
               mult_GF256(state[(i+1)%4][j], 0xB) ^\r
               mult_GF256(state[(i+2)%4][j], 0xD) ^\r
               mult_GF256(state[(i+3)%4][j], 9);\r
    }\r
    for (var i = 0; i < 4; i++)          // Place result back into column\r
      state[i][j] = b[i];\r
  }\r
}\r
\r
// Adds the current round key to the state information. Straightforward.\r
\r
function addRoundKey(state, roundKey) {\r
  for (var j = 0; j < Nb; j++) {                 // Step through columns...\r
    state[0][j] ^= (roundKey[j] & 0xFF);         // and XOR\r
    state[1][j] ^= ((roundKey[j]>>8) & 0xFF);\r
    state[2][j] ^= ((roundKey[j]>>16) & 0xFF);\r
    state[3][j] ^= ((roundKey[j]>>24) & 0xFF);\r
  }\r
}\r
\r
// This function creates the expanded key from the input (128/192/256-bit)\r
// key. The parameter key is an array of bytes holding the value of the key.\r
// The returned value is an array whose elements are the 32-bit words that \r
// make up the expanded key.\r
\r
function keyExpansion(key) {\r
  var expandedKey = new Array();\r
  var temp;\r
\r
  // in case the key size or parameters were changed...\r
  Nk = keySizeInBits / 32;                   \r
  Nb = blockSizeInBits / 32;\r
  Nr = roundsArray[Nk][Nb];\r
\r
  for (var j=0; j < Nk; j++)     // Fill in input key first\r
    expandedKey[j] = \r
      (key[4*j]) | (key[4*j+1]<<8) | (key[4*j+2]<<16) | (key[4*j+3]<<24);\r
\r
  // Now walk down the rest of the array filling in expanded key bytes as\r
  // per Rijndael's spec\r
  for (j = Nk; j < Nb * (Nr + 1); j++) {    // For each word of expanded key\r
    temp = expandedKey[j - 1];\r
    if (j % Nk == 0) \r
      temp = ( (SBox[(temp>>8) & 0xFF]) |\r
               (SBox[(temp>>16) & 0xFF]<<8) |\r
               (SBox[(temp>>24) & 0xFF]<<16) |\r
               (SBox[temp & 0xFF]<<24) ) ^ Rcon[Math.floor(j / Nk) - 1];\r
    else if (Nk > 6 && j % Nk == 4)\r
      temp = (SBox[(temp>>24) & 0xFF]<<24) |\r
             (SBox[(temp>>16) & 0xFF]<<16) |\r
             (SBox[(temp>>8) & 0xFF]<<8) |\r
             (SBox[temp & 0xFF]);\r
    expandedKey[j] = expandedKey[j-Nk] ^ temp;\r
  }\r
  return expandedKey;\r
}\r
\r
// Rijndael's round functions... \r
\r
function Round(state, roundKey) {\r
  byteSub(state, "encrypt");\r
  shiftRow(state, "encrypt");\r
  mixColumn(state, "encrypt");\r
  addRoundKey(state, roundKey);\r
}\r
\r
function InverseRound(state, roundKey) {\r
  addRoundKey(state, roundKey);\r
  mixColumn(state, "decrypt");\r
  shiftRow(state, "decrypt");\r
  byteSub(state, "decrypt");\r
}\r
\r
function FinalRound(state, roundKey) {\r
  byteSub(state, "encrypt");\r
  shiftRow(state, "encrypt");\r
  addRoundKey(state, roundKey);\r
}\r
\r
function InverseFinalRound(state, roundKey){\r
  addRoundKey(state, roundKey);\r
  shiftRow(state, "decrypt");\r
  byteSub(state, "decrypt");  \r
}\r
\r
// encrypt is the basic encryption function. It takes parameters\r
// block, an array of bytes representing a plaintext block, and expandedKey,\r
// an array of words representing the expanded key previously returned by\r
// keyExpansion(). The ciphertext block is returned as an array of bytes.\r
\r
function encrypt(block, expandedKey) {\r
  var i;  \r
  if (!block || block.length*8 != blockSizeInBits)\r
     return; \r
  if (!expandedKey)\r
     return;\r
\r
  block = packBytes(block);\r
  addRoundKey(block, expandedKey);\r
  for (i=1; i<Nr; i++) \r
    Round(block, expandedKey.slice(Nb*i, Nb*(i+1)));\r
  FinalRound(block, expandedKey.slice(Nb*Nr)); \r
  return unpackBytes(block);\r
}\r
\r
// decrypt is the basic decryption function. It takes parameters\r
// block, an array of bytes representing a ciphertext block, and expandedKey,\r
// an array of words representing the expanded key previously returned by\r
// keyExpansion(). The decrypted block is returned as an array of bytes.\r
\r
function decrypt(block, expandedKey) {\r
  var i;\r
  if (!block || block.length*8 != blockSizeInBits)\r
     return;\r
  if (!expandedKey)\r
     return;\r
\r
  block = packBytes(block);\r
  InverseFinalRound(block, expandedKey.slice(Nb*Nr)); \r
  for (i = Nr - 1; i>0; i--) \r
    InverseRound(block, expandedKey.slice(Nb*i, Nb*(i+1)));\r
  addRoundKey(block, expandedKey);\r
  return unpackBytes(block);\r
}\r
\r
/* !NEEDED\r
// This method takes a byte array (byteArray) and converts it to a string by\r
// applying String.fromCharCode() to each value and concatenating the result.\r
// The resulting string is returned. Note that this function SKIPS zero bytes\r
// under the assumption that they are padding added in formatPlaintext().\r
// Obviously, do not invoke this method on raw data that can contain zero\r
// bytes. It is really only appropriate for printable ASCII/Latin-1 \r
// values. Roll your own function for more robust functionality :)\r
\r
function byteArrayToString(byteArray) {\r
  var result = "";\r
  for(var i=0; i<byteArray.length; i++)\r
    if (byteArray[i] != 0) \r
      result += String.fromCharCode(byteArray[i]);\r
  return result;\r
}\r
*/\r
\r
// This function takes an array of bytes (byteArray) and converts them\r
// to a hexadecimal string. Array element 0 is found at the beginning of \r
// the resulting string, high nibble first. Consecutive elements follow\r
// similarly, for example [16, 255] --> "10ff". The function returns a \r
// string.\r
\r
function byteArrayToHex(byteArray) {\r
  var result = "";\r
  if (!byteArray)\r
    return;\r
  for (var i=0; i<byteArray.length; i++)\r
    result += ((byteArray[i]<16) ? "0" : "") + byteArray[i].toString(16);\r
\r
  return result;\r
}\r
\r
// This function converts a string containing hexadecimal digits to an \r
// array of bytes. The resulting byte array is filled in the order the\r
// values occur in the string, for example "10FF" --> [16, 255]. This\r
// function returns an array. \r
\r
function hexToByteArray(hexString) {\r
  var byteArray = [];\r
  if (hexString.length % 2)             // must have even length\r
    return;\r
  if (hexString.indexOf("0x") == 0 || hexString.indexOf("0X") == 0)\r
    hexString = hexString.substring(2);\r
  for (var i = 0; i<hexString.length; i += 2) \r
    byteArray[Math.floor(i/2)] = parseInt(hexString.slice(i, i+2), 16);\r
  return byteArray;\r
}\r
\r
// This function packs an array of bytes into the four row form defined by\r
// Rijndael. It assumes the length of the array of bytes is divisible by\r
// four. Bytes are filled in according to the Rijndael spec (starting with\r
// column 0, row 0 to 3). This function returns a 2d array.\r
\r
function packBytes(octets) {\r
  var state = new Array();\r
  if (!octets || octets.length % 4)\r
    return;\r
\r
  state[0] = new Array();  state[1] = new Array(); \r
  state[2] = new Array();  state[3] = new Array();\r
  for (var j=0; j<octets.length; j+= 4) {\r
     state[0][j/4] = octets[j];\r
     state[1][j/4] = octets[j+1];\r
     state[2][j/4] = octets[j+2];\r
     state[3][j/4] = octets[j+3];\r
  }\r
  return state;  \r
}\r
\r
// This function unpacks an array of bytes from the four row format preferred\r
// by Rijndael into a single 1d array of bytes. It assumes the input "packed"\r
// is a packed array. Bytes are filled in according to the Rijndael spec. \r
// This function returns a 1d array of bytes.\r
\r
function unpackBytes(packed) {\r
  var result = new Array();\r
  for (var j=0; j<packed[0].length; j++) {\r
    result[result.length] = packed[0][j];\r
    result[result.length] = packed[1][j];\r
    result[result.length] = packed[2][j];\r
    result[result.length] = packed[3][j];\r
  }\r
  return result;\r
}\r
\r
// This function takes a prospective plaintext (string or array of bytes)\r
// and pads it with pseudorandom bytes if its length is not a multiple of the block \r
// size. If plaintext is a string, it is converted to an array of bytes\r
// in the process. The type checking can be made much nicer using the \r
// instanceof operator, but this operator is not available until IE5.0 so I \r
// chose to use the heuristic below. \r
\r
function formatPlaintext(plaintext) {\r
  var bpb = blockSizeInBits / 8;               // bytes per block\r
  var i;\r
\r
  // if primitive string or String instance\r
  if ((!((typeof plaintext == "object") &&\r
        ((typeof (plaintext[0])) == "number"))) &&\r
      ((typeof plaintext == "string") || plaintext.indexOf)) {\r
    plaintext = plaintext.split("");\r
    // Unicode issues here (ignoring high byte)\r
    for (i=0; i<plaintext.length; i++)\r
      plaintext[i] = plaintext[i].charCodeAt(0) & 0xFF;\r
  } \r
\r
  i = plaintext.length % bpb;\r
  if (i > 0) {\r
    plaintext = plaintext.concat(getRandomBytes(bpb - i));\r
  }\r
  \r
  return plaintext;\r
}\r
\r
// Returns an array containing "howMany" random bytes.\r
\r
function getRandomBytes(howMany) {\r
    var i, bytes = new Array();\r
    \r
    for (i = 0; i < howMany; i++) {\r
        bytes[i] = prng.nextInt(255);\r
    }\r
    return bytes;\r
}\r
\r
// rijndaelEncrypt(plaintext, key, mode)\r
// Encrypts the plaintext using the given key and in the given mode. \r
// The parameter "plaintext" can either be a string or an array of bytes. \r
// The parameter "key" must be an array of key bytes. If you have a hex \r
// string representing the key, invoke hexToByteArray() on it to convert it \r
// to an array of bytes. The third parameter "mode" is a string indicating\r
// the encryption mode to use, either "ECB" or "CBC". If the parameter is\r
// omitted, ECB is assumed.\r
// \r
// An array of bytes representing the cihpertext is returned. To convert \r
// this array to hex, invoke byteArrayToHex() on it.\r
\r
function rijndaelEncrypt(plaintext, key, mode) {\r
  var expandedKey, i, aBlock;\r
  var bpb = blockSizeInBits / 8;          // bytes per block\r
  var ct;                                 // ciphertext\r
\r
  if (!plaintext || !key)\r
    return;\r
  if (key.length*8 != keySizeInBits)\r
    return; \r
  if (mode == "CBC") {\r
    ct = getRandomBytes(bpb);             // get IV\r
//dump("IV", byteArrayToHex(ct));\r
  } else {\r
    mode = "ECB";\r
    ct = new Array();\r
  }\r
\r
  // convert plaintext to byte array and pad with zeros if necessary. \r
  plaintext = formatPlaintext(plaintext);\r
\r
  expandedKey = keyExpansion(key);\r
  \r
  for (var block = 0; block < plaintext.length / bpb; block++) {\r
    aBlock = plaintext.slice(block * bpb, (block + 1) * bpb);\r
    if (mode == "CBC") {\r
      for (var i = 0; i < bpb; i++) {\r
        aBlock[i] ^= ct[(block * bpb) + i];\r
      }\r
    }\r
    ct = ct.concat(encrypt(aBlock, expandedKey));\r
  }\r
\r
  return ct;\r
}\r
\r
// rijndaelDecrypt(ciphertext, key, mode)\r
// Decrypts the using the given key and mode. The parameter "ciphertext" \r
// must be an array of bytes. The parameter "key" must be an array of key \r
// bytes. If you have a hex string representing the ciphertext or key, \r
// invoke hexToByteArray() on it to convert it to an array of bytes. The\r
// parameter "mode" is a string, either "CBC" or "ECB".\r
// \r
// An array of bytes representing the plaintext is returned. To convert \r
// this array to a hex string, invoke byteArrayToHex() on it. To convert it \r
// to a string of characters, you can use byteArrayToString().\r
\r
function rijndaelDecrypt(ciphertext, key, mode) {\r
  var expandedKey;\r
  var bpb = blockSizeInBits / 8;          // bytes per block\r
  var pt = new Array();                   // plaintext array\r
  var aBlock;                             // a decrypted block\r
  var block;                              // current block number\r
\r
  if (!ciphertext || !key || typeof ciphertext == "string")\r
    return;\r
  if (key.length*8 != keySizeInBits)\r
    return; \r
  if (!mode) {\r
    mode = "ECB";                         // assume ECB if mode omitted\r
  }\r
\r
  expandedKey = keyExpansion(key);\r
 \r
  // work backwards to accomodate CBC mode \r
  for (block=(ciphertext.length / bpb)-1; block>0; block--) {\r
    aBlock = \r
     decrypt(ciphertext.slice(block*bpb,(block+1)*bpb), expandedKey);\r
    if (mode == "CBC") \r
      for (var i=0; i<bpb; i++) \r
        pt[(block-1)*bpb + i] = aBlock[i] ^ ciphertext[(block-1)*bpb + i];\r
    else \r
      pt = aBlock.concat(pt);\r
  }\r
\r
  // do last block if ECB (skips the IV in CBC)\r
  if (mode == "ECB")\r
    pt = decrypt(ciphertext.slice(0, bpb), expandedKey).concat(pt);\r
\r
  return pt;\r
}\r