keysafe-0.20160914: ExpensiveHash.hs

{-# LANGUAGE OverloadedStrings #-}

{- Copyright 2016 Joey Hess <id@joeyh.name>
 -
 - Licensed under the GNU AGPL version 3 or higher.
 -}

module ExpensiveHash where

import Tunables
import Cost
import Serialization ()
import qualified Data.Text as T
import qualified Data.ByteString as B
import qualified Crypto.Argon2 as Argon2
import Raaz.Core.Encode
import Data.Monoid

-- | A hash that is expensive to calculate.
--
-- This is a lynchpin of keysafe's security, because using this hash
-- as an encryption key forces brute force attackers to generate
-- hashes over and over again, taking a very long time.
data ExpensiveHash = ExpensiveHash (Cost CreationOp) T.Text
	deriving (Show)

instance HasCreationCost ExpensiveHash where
	getCreationCost (ExpensiveHash c _) = c

data Salt t = Salt t

expensiveHash :: Encodable t => ExpensiveHashTunable -> Salt t -> B.ByteString -> ExpensiveHash
expensiveHash (UseArgon2 cost opts) (Salt s) b = ExpensiveHash cost $
	-- Using hashEncoded here and not hash,
	-- because of this bug:
	-- https://github.com/ocharles/argon2/issues/3
	Argon2.hashEncoded opts b argonsalt
  where
	-- argon salt cannot be shorter than 8 bytes, so pad with spaces.
	argonsalt = 
		let sb = toByteString s
		in sb <> B.replicate (8 - B.length sb ) 32