shadowsocks/src/encrypt.coffee

a tunnel proxy that help you get through firewalls

###
  Copyright (c) 2014 clowwindy
  
  Permission is hereby granted, free of charge, to any person obtaining a copy
  of this software and associated documentation files (the "Software"), to deal
  in the Software without restriction, including without limitation the rights
  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
  copies of the Software, and to permit persons to whom the Software is
  furnished to do so, subject to the following conditions:
  
  The above copyright notice and this permission notice shall be included in
  all copies or substantial portions of the Software.
  
  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  SOFTWARE.
###

crypto = require("crypto")
util = require("util")
merge_sort = require("./merge_sort").merge_sort
int32Max = Math.pow(2, 32)

cachedTables = {} # password: [encryptTable, decryptTable]

getTable = (key) ->
  if cachedTables[key]
    return cachedTables[key]
  util.log "calculating ciphers"
  table = new Array(256)
  decrypt_table = new Array(256)
  md5sum = crypto.createHash("md5")
  md5sum.update key
  hash = new Buffer(md5sum.digest(), "binary")
  al = hash.readUInt32LE(0)
  ah = hash.readUInt32LE(4)
  i = 0

  while i < 256
    table[i] = i
    i++
  i = 1

  while i < 1024
    table = merge_sort(table, (x, y) ->
      ((ah % (x + i)) * int32Max + al) % (x + i) - ((ah % (y + i)) * int32Max + al) % (y + i)
    )
    i++
  i = 0
  while i < 256
    decrypt_table[table[i]] = i
    ++i
  result = [table, decrypt_table]
  cachedTables[key] = result
  result
  
substitute = (table, buf) ->
  i = 0

  while i < buf.length
    buf[i] = table[buf[i]]
    i++
  buf

bytes_to_key_results = {}

EVP_BytesToKey = (password, key_len, iv_len) ->
  if bytes_to_key_results["#{password}:#{key_len}:#{iv_len}"]
    return bytes_to_key_results["#{password}:#{key_len}:#{iv_len}"]
  m = []
  i = 0
  count = 0
  while count < key_len + iv_len
    md5 = crypto.createHash('md5')
    data = password
    if i > 0
      data = Buffer.concat([m[i - 1], password])
    md5.update(data)
    d = md5.digest()
    m.push(d)
    count += d.length
    i += 1
  ms = Buffer.concat(m)
  key = ms.slice(0, key_len)
  iv = ms.slice(key_len, key_len + iv_len)
  bytes_to_key_results[password] = [key, iv]
  return [key, iv]


method_supported =
  'aes-128-cfb': [16, 16]
  'aes-192-cfb': [24, 16]
  'aes-256-cfb': [32, 16]
  'bf-cfb': [16, 8]
  'camellia-128-cfb': [16, 16]
  'camellia-192-cfb': [24, 16]
  'camellia-256-cfb': [32, 16]
  'cast5-cfb': [16, 8]
  'des-cfb': [8, 8]
  'idea-cfb': [16, 8]
  'rc2-cfb': [16, 8]
  'rc4': [16, 0]
  'rc4-md5': [16, 16]
  'seed-cfb': [16, 16]


create_rc4_md5_cipher = (key, iv, op) ->
  md5 = crypto.createHash('md5')
  md5.update(key)
  md5.update(iv)
  rc4_key = md5.digest()
  if op == 1
    return crypto.createCipheriv('rc4', rc4_key, '')
  else
    return crypto.createDecipheriv('rc4', rc4_key, '')


class Encryptor
  constructor: (@key, @method) ->
    @iv_sent = false
    if @method == 'table'
      @method = null
    if @method?
      @cipher = @get_cipher(@key, @method, 1, crypto.randomBytes(32))
    else
      [@encryptTable, @decryptTable] = getTable(@key)
      
  get_cipher_len: (method) ->
    method = method.toLowerCase()
    m = method_supported[method]
    return m

  get_cipher: (password, method, op, iv) ->
    method = method.toLowerCase()
    password = new Buffer(password, 'binary')
    m = @get_cipher_len(method)
    if m?
      [key, iv_] = EVP_BytesToKey(password, m[0], m[1])
      if not iv?
        iv = iv_
      if op == 1
        @cipher_iv = iv.slice(0, m[1])
      iv = iv.slice(0, m[1])
      if method == 'rc4-md5'
        return create_rc4_md5_cipher(key, iv, op)
      else
        if op == 1
          return crypto.createCipheriv(method, key, iv)
        else
          return crypto.createDecipheriv(method, key, iv)

  encrypt: (buf) ->
    if @method?
      result = @cipher.update buf
      if @iv_sent
        return result
      else
        @iv_sent = true
        return Buffer.concat([@cipher_iv, result])
    else
      substitute @encryptTable, buf
      
  decrypt: (buf) ->
    if @method?
      if not @decipher?
        decipher_iv_len = @get_cipher_len(@method)[1]
        decipher_iv = buf.slice(0, decipher_iv_len) 
        @decipher = @get_cipher(@key, @method, 0, decipher_iv)
        result = @decipher.update(buf.slice(decipher_iv_len))
        return result
      else
        result = @decipher.update(buf)
        return result
    else
      substitute @decryptTable, buf

encryptAll = (password, method, op, data) ->
  if method == 'table'
    method = null
  if not method?
    [encryptTable, decryptTable] = getTable(password)
    if op is 0
      return substitute(decryptTable, data)
    else
      return substitute(encryptTable, data)
  else
    result = []
    method = method.toLowerCase()
    [keyLen, ivLen] = method_supported[method]
    password = Buffer(password, 'binary')
    [key, iv_] = EVP_BytesToKey(password, keyLen, ivLen) 
    if op == 1
      iv = crypto.randomBytes ivLen
      result.push iv
    else
      iv = data.slice 0, ivLen
      data = data.slice ivLen
    if method == 'rc4-md5'
      cipher = create_rc4_md5_cipher(key, iv, op)
    else
      if op == 1
        cipher = crypto.createCipheriv(method, key, iv)
      else
        cipher = crypto.createDecipheriv(method, key, iv)
    result.push cipher.update(data)
    result.push cipher.final()
    return Buffer.concat result


exports.Encryptor = Encryptor
exports.getTable = getTable
exports.encryptAll = encryptAll