aes.js

/*
 *
 * This file contains an adaptation of the AES decryption algorithm
 * from the Standford Javascript Cryptography Library. That work is
 * covered by the following copyright and permissions notice:
 *
 * Copyright 2009-2010 Emily Stark, Mike Hamburg, Dan Boneh.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 *
 * 2. Redistributions in binary form must reproduce the above
 *    copyright notice, this list of conditions and the following
 *    disclaimer in the documentation and/or other materials provided
 *    with the distribution.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
 * IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 * The views and conclusions contained in the software and documentation
 * are those of the authors and should not be interpreted as representing
 * official policies, either expressed or implied, of the authors.
 */
class AES {

  /**
   * Schedule out an AES key for both encryption and decryption. This
   * is a low-level class. Use a cipher mode to do bulk encryption.
   *
   * @constructor
   * @param key {Array} The key as an array of 4, 6 or 8 words.
   */
  constructor(key) {
    /**
     * The expanded S-box and inverse S-box tables. These will be computed
     * on the client so that we don't have to send them down the wire.
     *
     * There are two tables, _tables[0] is for encryption and
     * _tables[1] is for decryption.
     *
     * The first 4 sub-tables are the expanded S-box with MixColumns. The
     * last (_tables[01][4]) is the S-box itself.
     *
     * @private
     */
    this._tables = [[[],[],[],[],[]],[[],[],[],[],[]]];

    this._precompute();

    var i, j, tmp,
    encKey, decKey,
    sbox = this._tables[0][4], decTable = this._tables[1],
    keyLen = key.length, rcon = 1;

    if (keyLen !== 4 && keyLen !== 6 && keyLen !== 8) {
      throw new Error('Invalid aes key size=' + keyLen);
    }

    encKey = key.slice(0);
    decKey = [];
    this._key = [encKey, decKey];

    // schedule encryption keys
    for (i = keyLen; i < 4 * keyLen + 28; i++) {
      tmp = encKey[i-1];

      // apply sbox
      if (i%keyLen === 0 || (keyLen === 8 && i%keyLen === 4)) {
        tmp = sbox[tmp>>>24]<<24 ^ sbox[tmp>>16&255]<<16 ^ sbox[tmp>>8&255]<<8 ^ sbox[tmp&255];

        // shift rows and add rcon
        if (i%keyLen === 0) {
          tmp = tmp<<8 ^ tmp>>>24 ^ rcon<<24;
          rcon = rcon<<1 ^ (rcon>>7)*283;
        }
      }

      encKey[i] = encKey[i-keyLen] ^ tmp;
    }

    // schedule decryption keys
    for (j = 0; i; j++, i--) {
      tmp = encKey[j&3 ? i : i - 4];
      if (i<=4 || j<4) {
        decKey[j] = tmp;
      } else {
        decKey[j] = decTable[0][sbox[tmp>>>24      ]] ^
          decTable[1][sbox[tmp>>16  & 255]] ^
          decTable[2][sbox[tmp>>8   & 255]] ^
          decTable[3][sbox[tmp      & 255]];
      }
    }
  }

  /**
   * Expand the S-box tables.
   *
   * @private
   */
  _precompute() {
    var encTable = this._tables[0], decTable = this._tables[1],
    sbox = encTable[4], sboxInv = decTable[4],
    i, x, xInv, d=[], th=[], x2, x4, x8, s, tEnc, tDec;

    // Compute double and third tables
    for (i = 0; i < 256; i++) {
      th[( d[i] = i<<1 ^ (i>>7)*283 )^i]=i;
    }

    for (x = xInv = 0; !sbox[x]; x ^= x2 || 1, xInv = th[xInv] || 1) {
      // Compute sbox
      s = xInv ^ xInv<<1 ^ xInv<<2 ^ xInv<<3 ^ xInv<<4;
      s = s>>8 ^ s&255 ^ 99;
      sbox[x] = s;
      sboxInv[s] = x;

      // Compute MixColumns
      x8 = d[x4 = d[x2 = d[x]]];
      tDec = x8*0x1010101 ^ x4*0x10001 ^ x2*0x101 ^ x*0x1010100;
      tEnc = d[s]*0x101 ^ s*0x1010100;

      for (i = 0; i < 4; i++) {
        encTable[i][x] = tEnc = tEnc<<24 ^ tEnc>>>8;
        decTable[i][s] = tDec = tDec<<24 ^ tDec>>>8;
      }
    }

    // Compactify. Considerable speedup on Firefox.
    for (i = 0; i < 5; i++) {
      encTable[i] = encTable[i].slice(0);
      decTable[i] = decTable[i].slice(0);
    }
  }

  /**
   * Decrypt 16 bytes, specified as four 32-bit words.
   * @param encrypted0 {number} the first word to decrypt
   * @param encrypted1 {number} the second word to decrypt
   * @param encrypted2 {number} the third word to decrypt
   * @param encrypted3 {number} the fourth word to decrypt
   * @param out {Int32Array} the array to write the decrypted words
   * into
   * @param offset {number} the offset into the output array to start
   * writing results
   * @return {Array} The plaintext.
   */
  decrypt(encrypted0, encrypted1, encrypted2, encrypted3, out, offset) {
    var key = this._key[1],
    // state variables a,b,c,d are loaded with pre-whitened data
    a = encrypted0 ^ key[0],
    b = encrypted3 ^ key[1],
    c = encrypted2 ^ key[2],
    d = encrypted1 ^ key[3],
    a2, b2, c2,

    nInnerRounds = key.length / 4 - 2, // key.length === 2 ?
    i,
    kIndex = 4,
    table = this._tables[1],

    // load up the tables
    table0    = table[0],
    table1    = table[1],
    table2    = table[2],
    table3    = table[3],
    sbox  = table[4];

    // Inner rounds. Cribbed from OpenSSL.
    for (i = 0; i < nInnerRounds; i++) {
      a2 = table0[a>>>24] ^ table1[b>>16 & 255] ^ table2[c>>8 & 255] ^ table3[d & 255] ^ key[kIndex];
      b2 = table0[b>>>24] ^ table1[c>>16 & 255] ^ table2[d>>8 & 255] ^ table3[a & 255] ^ key[kIndex + 1];
      c2 = table0[c>>>24] ^ table1[d>>16 & 255] ^ table2[a>>8 & 255] ^ table3[b & 255] ^ key[kIndex + 2];
      d  = table0[d>>>24] ^ table1[a>>16 & 255] ^ table2[b>>8 & 255] ^ table3[c & 255] ^ key[kIndex + 3];
      kIndex += 4;
      a=a2; b=b2; c=c2;
    }

    // Last round.
    for (i = 0; i < 4; i++) {
      out[(3 & -i) + offset] =
        sbox[a>>>24      ]<<24 ^
        sbox[b>>16  & 255]<<16 ^
        sbox[c>>8   & 255]<<8  ^
        sbox[d      & 255]     ^
        key[kIndex++];
      a2=a; a=b; b=c; c=d; d=a2;
    }
  }
}

export default AES;