aes.js

/**
 * @file 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.
 */

/**
 * Expand the S-box tables.
 *
 * @private
 */
const precompute = function() {
  const tables = [[[], [], [], [], []], [[], [], [], [], []]];
  const encTable = tables[0];
  const decTable = tables[1];
  const sbox = encTable[4];
  const sboxInv = decTable[4];
  let i;
  let x;
  let xInv;
  const d = [];
  const th = [];
  let x2;
  let x4;
  let x8;
  let s;
  let tEnc;
  let 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);
  }
  return tables;
};
let aesTables = null;

/**
 * Schedule out an AES key for both encryption and decryption. This
 * is a low-level class. Use a cipher mode to do bulk encryption.
 *
 * @class AES
 * @param key {Array} The key as an array of 4, 6 or 8 words.
 */
export default class AES {
  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
    */
    // if we have yet to precompute the S-box tables
    // do so now
    if (!aesTables) {
      aesTables = precompute();
    }
    // then make a copy of that object for use
    this._tables = [[aesTables[0][0].slice(),
      aesTables[0][1].slice(),
      aesTables[0][2].slice(),
      aesTables[0][3].slice(),
      aesTables[0][4].slice()],
    [aesTables[1][0].slice(),
      aesTables[1][1].slice(),
      aesTables[1][2].slice(),
      aesTables[1][3].slice(),
      aesTables[1][4].slice()]];
    let i;
    let j;
    let tmp;
    const sbox = this._tables[0][4];
    const decTable = this._tables[1];
    const keyLen = key.length;
    let rcon = 1;

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

    const encKey = key.slice(0);
    const 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]];
      }
    }
  }

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

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

    // load up the tables
    const table0 = table[0];
    const table1 = table[1];
    const table2 = table[2];
    const table3 = table[3];
    const 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;
    }
  }
}