module Cryptdoh

# File lib/cryptdoh.rb, line 66
def self._check_password_length(password)
  raise UserError, "Crappy password: too short. Must be at least 8 bytes" unless password.size >= MIN_PASSWORD_LENGTH
end

# File lib/cryptdoh.rb, line 61
def self._check_password_strength(password)
  c = CrackLib::Fascist(password)
  raise UserError, "Crappy password: #{c.reason}" unless c.ok?
end

# File lib/cryptdoh.rb, line 86
def self._decode(data)
  Base64.decode64(data)
rescue
  raise EvilError, 'Bad base64 data'
end

# File lib/cryptdoh.rb, line 82
def self._encode(data)
  Base64.encode64(data).chomp
end

# File lib/cryptdoh.rb, line 77
def self._hmac(key, message)
  # Only require 128 bits of security, so cut in half
  OpenSSL::HMAC.digest(DIGEST, key, message)[0..15]
end

# File lib/cryptdoh.rb, line 70
def self._kdf(password, salt = nil)
  salt ||= SecureRandom.random_bytes(SALT_LENGTH)
  raise UserError, "Salt is the wrong size" unless salt.size == SALT_LENGTH
  key = OpenSSL::PKCS5.pbkdf2_hmac(password, salt, ITERATIONS, KEY_LENGTH * 2, DIGEST)
  [salt, key]
end

# File lib/cryptdoh.rb, line 92
def self._verify
  message = 'this is a secret message'
  password = 'dZ]av}a]i4qK2:1Z:t |Ju.'

  decrypt(password, encrypt(password, message)) == message
rescue
  false
end

# File lib/cryptdoh.rb, line 43
def self.decrypt(password, message)
  (version, encoded_iv, encoded_salt, encoded_ciphertext, encoded_hmac) = message.split('.')

  (salt, key) = _kdf(password, _decode(encoded_salt))
  cipher_key = key[0..KEY_LENGTH-1]
  hmac_key = key[KEY_LENGTH..-1]

  hmac = _hmac(hmac_key, [version, encoded_iv, encoded_salt, encoded_ciphertext].join('.'))
  raise EvilError, 'Invalid HMAC' unless _decode(encoded_hmac) == hmac

  decipher = OpenSSL::Cipher::AES.new(KEY_LENGTH * 8, :CBC)
  decipher.decrypt
  decipher.iv = _decode(encoded_iv)
  decipher.key = cipher_key

  decipher.update(_decode(encoded_ciphertext)) + decipher.final
end

# File lib/cryptdoh.rb, line 22
def self.encrypt(password, message, args = {})
  _check_password_length(password)
  _check_password_strength(password) unless args[:skip_strength_check]

  (salt, key) = _kdf(password)
  cipher_key = key[0..KEY_LENGTH-1]
  hmac_key = key[KEY_LENGTH..-1]

  cipher = OpenSSL::Cipher::AES.new(KEY_LENGTH * 8, :CBC)
  cipher.encrypt
  iv = cipher.random_iv
  cipher.key = cipher_key

  ciphertext = cipher.update(message) + cipher.final

  cipher_message = [VERSION, _encode(iv), _encode(salt), _encode(ciphertext)].join('.')
  hmac = _hmac(hmac_key, cipher_message)

  [cipher_message, _encode(hmac)].join('.')
end