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')
}

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(password, config.key, config.iv)
  return createDecipheriv(suite, keys.key, keys.iv)
}
exports.createDecipher = createDecipher
exports.createDecipheriv = createDecipheriv