authCipher.js

var aes = require('./aes')
var Transform = require('./cipherBase')
var inherits = require('inherits')
var GHASH = require('./ghash')
var xor = require('./xor')
inherits(StreamCipher, Transform)
module.exports = StreamCipher

function StreamCipher (mode, key, iv, decrypt) {
  if (!(this instanceof StreamCipher)) {
    return new StreamCipher(mode, key, iv)
  }
  Transform.call(this)
  this._finID = Buffer.concat([iv, new Buffer([0, 0, 0, 1])])
  iv = Buffer.concat([iv, new Buffer([0, 0, 0, 2])])
  this._cipher = new aes.AES(key)
  this._prev = new Buffer(iv.length)
  this._cache = new Buffer('')
  this._secCache = new Buffer('')
  this._decrypt = decrypt
  this._alen = 0
  this._len = 0
  iv.copy(this._prev)
  this._mode = mode
  var h = new Buffer(4)
  h.fill(0)
  this._ghash = new GHASH(this._cipher.encryptBlock(h))
  this._authTag = null
  this._called = false
}
StreamCipher.prototype._update = function (chunk) {
  if (!this._called && this._alen) {
    var rump = 16 - (this._alen % 16)
    if (rump < 16) {
      rump = new Buffer(rump)
      rump.fill(0)
      this._ghash.update(rump)
    }
  }
  this._called = true
  var out = this._mode.encrypt(this, chunk)
  if (this._decrypt) {
    this._ghash.update(chunk)
  } else {
    this._ghash.update(out)
  }
  this._len += chunk.length
  return out
}
StreamCipher.prototype._final = function () {
  if (this._decrypt && !this._authTag) {
    throw new Error('Unsupported state or unable to authenticate data')
  }
  var tag = xor(this._ghash.final(this._alen * 8, this._len * 8), this._cipher.encryptBlock(this._finID))
  if (this._decrypt) {
    if (xorTest(tag, this._authTag)) {
      throw new Error('Unsupported state or unable to authenticate data')
    }
  } else {
    this._authTag = tag
  }
  this._cipher.scrub()
}
StreamCipher.prototype.getAuthTag = function getAuthTag () {
  if (!this._decrypt && Buffer.isBuffer(this._authTag)) {
    return this._authTag
  } else {
    throw new Error('Attempting to get auth tag in unsupported state')
  }
}
StreamCipher.prototype.setAuthTag = function setAuthTag (tag) {
  if (this._decrypt) {
    this._authTag = tag
  } else {
    throw new Error('Attempting to set auth tag in unsupported state')
  }
}
StreamCipher.prototype.setAAD = function setAAD (buf) {
  if (!this._called) {
    this._ghash.update(buf)
    this._alen += buf.length
  } else {
    throw new Error('Attempting to set AAD in unsupported state')
  }
}
function xorTest (a, b) {
  var out = 0
  if (a.length !== b.length) {
    out++
  }
  var len = Math.min(a.length, b.length)
  var i = -1
  while (++i < len) {
    out += (a[i] ^ b[i])
  }
  return out
}