browserify-aes/decrypter.js

var aes = require('./aes');
var Transform = require('./cipherBase');
var inherits = require('inherits');
var modes = require('./modes');
var StreamCipher = require('./streamCipher');
var AuthCipher = require('./authCipher');
var ebtk = require('./EVP_BytesToKey');

inherits(Decipher, Transform);
function Decipher(mode, key, iv) {
  if (!(this instanceof Decipher)) {
    return new Decipher(mode, key, iv);
  }
  Transform.call(this);
  this._cache = new Splitter();
  this._last = void 0;
  this._cipher = new aes.AES(key);
  this._prev = new Buffer(iv.length);
  iv.copy(this._prev);
  this._mode = mode;
  this._autopadding = true;
}
Decipher.prototype._update = function (data) {
  this._cache.add(data);
  var chunk;
  var thing;
  var out = [];
  while ((chunk = this._cache.get(this._autopadding))) {
    thing = this._mode.decrypt(this, chunk);
    out.push(thing);
  }
  return Buffer.concat(out);
};
Decipher.prototype._final = function () {
  var chunk = this._cache.flush();
  if (this._autopadding) {
    return unpad(this._mode.decrypt(this, chunk));
  } else if (chunk) {
    throw new Error('data not multiple of block length');
  }
};
Decipher.prototype.setAutoPadding = function (setTo) {
  this._autopadding = !!setTo;
};
function Splitter() {
   if (!(this instanceof Splitter)) {
    return new Splitter();
  }
  this.cache = new Buffer('');
}
Splitter.prototype.add = function (data) {
  this.cache = Buffer.concat([this.cache, data]);
};

Splitter.prototype.get = function (autoPadding) {
  var out;
  if (autoPadding) {
    if (this.cache.length > 16) {
      out = this.cache.slice(0, 16);
      this.cache = this.cache.slice(16);
      return out;
    }
  } else {
    if (this.cache.length >= 16) {
      out = this.cache.slice(0, 16);
      this.cache = this.cache.slice(16);
      return out;
    }
  }
  return null;
};
Splitter.prototype.flush = function () {
  if (this.cache.length) {
    return this.cache;
  }
};
function unpad(last) {
  var padded = last[15];
  var i = -1;
  while (++i < padded) {
    if (last[(i + (16 - padded))] !== padded) {
      throw new Error('unable to decrypt data');
    }
  }
  if (padded === 16) {
    return;
  }
  return last.slice(0, 16 - padded);
}

var modelist = {
  ECB: require('./modes/ecb'),
  CBC: require('./modes/cbc'),
  CFB: require('./modes/cfb'),
  CFB8: require('./modes/cfb8'),
  CFB1: require('./modes/cfb1'),
  OFB: require('./modes/ofb'),
  CTR: require('./modes/ctr'),
  GCM: require('./modes/ctr')
};

module.exports = function (crypto) {
  function createDecipheriv(suite, password, iv) {
    var config = modes[suite.toLowerCase()];
    if (!config) {
      throw new TypeError('invalid suite type');
    }
    if (typeof iv === 'string') {
      iv = new Buffer(iv);
    }
    if (typeof password === 'string') {
      password = new Buffer(password);
    }
    if (password.length !== config.key/8) {
      throw new TypeError('invalid key length ' + password.length);
    }
    if (iv.length !== config.iv) {
      throw new TypeError('invalid iv length ' + iv.length);
    }
    if (config.type === 'stream') {
      return new StreamCipher(modelist[config.mode], password, iv, true);
    } else if (config.type === 'auth') {
      return new AuthCipher(modelist[config.mode], password, iv, true);
    }
    return new Decipher(modelist[config.mode], password, iv);
  }

  function createDecipher (suite, password) {
    var config = modes[suite.toLowerCase()];
    if (!config) {
      throw new TypeError('invalid suite type');
    }
    var keys = ebtk(crypto, password, config.key, config.iv);
    return createDecipheriv(suite, keys.key, keys.iv);
  }
  return {
    createDecipher: createDecipher,
    createDecipheriv: createDecipheriv
  };
};