@hchuanz/aes-forge/lib/cipherModes.js

JavaScript AES node-forge.

/**
 * Supported cipher modes.
 *
 * @author Dave Longley
 *
 * Copyright (c) 2010-2014 Digital Bazaar, Inc.
 */
var forge = require('./forge');
require('./util');

forge.cipher = forge.cipher || {};

// supported cipher modes
var modes = module.exports = forge.cipher.modes = forge.cipher.modes || {};

/** Electronic codebook (ECB) (Don't use this; it's not secure) **/

/** Cipher-block Chaining (CBC) **/

modes.cbc = function(options) {
  options = options || {};
  this.name = 'CBC';
  this.cipher = options.cipher;
  this.blockSize = options.blockSize || 16;
  this._ints = this.blockSize / 4;
  this._inBlock = new Array(this._ints);
  this._outBlock = new Array(this._ints);
};

modes.cbc.prototype.start = function(options) {
  // Note: legacy support for using IV residue (has security flaws)
  // if IV is null, reuse block from previous processing
  if(options.iv === null) {
    // must have a previous block
    if(!this._prev) {
      throw new Error('Invalid IV parameter.');
    }
    this._iv = this._prev.slice(0);
  } else if(!('iv' in options)) {
    throw new Error('Invalid IV parameter.');
  } else {
    // save IV as "previous" block
    this._iv = transformIV(options.iv, this.blockSize);
    this._prev = this._iv.slice(0);
  }
};

modes.cbc.prototype.encrypt = function(input, output, finish) {
  // not enough input to encrypt
  if(input.length() < this.blockSize && !(finish && input.length() > 0)) {
    return true;
  }

  // get next block
  // CBC XOR's IV (or previous block) with plaintext
  for(var i = 0; i < this._ints; ++i) {
    this._inBlock[i] = this._prev[i] ^ input.getInt32();
  }

  // encrypt block
  this.cipher.encrypt(this._inBlock, this._outBlock);

  // write output, save previous block
  for(var i = 0; i < this._ints; ++i) {
    output.putInt32(this._outBlock[i]);
  }
  this._prev = this._outBlock;
};

modes.cbc.prototype.decrypt = function(input, output, finish) {
  // not enough input to decrypt
  if(input.length() < this.blockSize && !(finish && input.length() > 0)) {
    return true;
  }

  // get next block
  for(var i = 0; i < this._ints; ++i) {
    this._inBlock[i] = input.getInt32();
  }

  // decrypt block
  this.cipher.decrypt(this._inBlock, this._outBlock);

  // write output, save previous ciphered block
  // CBC XOR's IV (or previous block) with ciphertext
  for(var i = 0; i < this._ints; ++i) {
    output.putInt32(this._prev[i] ^ this._outBlock[i]);
  }
  this._prev = this._inBlock.slice(0);
};

modes.cbc.prototype.pad = function(input, options) {
  // add PKCS#7 padding to block (each pad byte is the
  // value of the number of pad bytes)
  var padding = (input.length() === this.blockSize ?
    this.blockSize : (this.blockSize - input.length()));
  input.fillWithByte(padding, padding);
  return true;
};

modes.cbc.prototype.unpad = function(output, options) {
  // check for error: input data not a multiple of blockSize
  if(options.overflow > 0) {
    return false;
  }

  // ensure padding byte count is valid
  var len = output.length();
  var count = output.at(len - 1);
  if(count > (this.blockSize << 2)) {
    return false;
  }

  // trim off padding bytes
  output.truncate(count);
  return true;
};


/** Utility functions */

function transformIV(iv, blockSize) {
  if(typeof iv === 'string') {
    // convert iv string into byte buffer
    iv = forge.util.createBuffer(iv);
  }

  if(forge.util.isArray(iv) && iv.length > 4) {
    // convert iv byte array into byte buffer
    var tmp = iv;
    iv = forge.util.createBuffer();
    for(var i = 0; i < tmp.length; ++i) {
      iv.putByte(tmp[i]);
    }
  }

  if(iv.length() < blockSize) {
    throw new Error(
      'Invalid IV length; got ' + iv.length() +
      ' bytes and expected ' + blockSize + ' bytes.');
  }

  if(!forge.util.isArray(iv)) {
    // convert iv byte buffer into 32-bit integer array
    var ints = [];
    var blocks = blockSize / 4;
    for(var i = 0; i < blocks; ++i) {
      ints.push(iv.getInt32());
    }
    iv = ints;
  }

  return iv;
}

function inc32(block) {
  // increment last 32 bits of block only
  block[block.length - 1] = (block[block.length - 1] + 1) & 0xFFFFFFFF;
}

function from64To32(num) {
  // convert 64-bit number to two BE Int32s
  return [(num / 0x100000000) | 0, num & 0xFFFFFFFF];
}