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bundled/Crypto/Random/ChaChaDRG.hs

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+-- |
+-- Module      : Crypto.Random.ChaChaDRG
+-- License     : BSD-style
+-- Maintainer  : Vincent Hanquez <vincent@snarc.org>
+-- Stability   : stable
+-- Portability : good
+--
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+module Crypto.Random.ChaChaDRG
+    ( ChaChaDRG
+    , initialize
+    , initializeWords
+    ) where
+
+import           Crypto.Random.Types
+import           Crypto.Internal.Imports
+import           Crypto.Internal.ByteArray (ByteArray, ByteArrayAccess, ScrubbedBytes)
+import qualified Crypto.Internal.ByteArray as B
+import           Foreign.Storable (pokeElemOff)
+
+import qualified Crypto.Cipher.ChaCha as C
+
+instance DRG ChaChaDRG where
+    randomBytesGenerate = generate
+
+-- | ChaCha Deterministic Random Generator
+newtype ChaChaDRG = ChaChaDRG C.StateSimple
+    deriving (NFData)
+
+-- | Initialize a new ChaCha context with the number of rounds,
+-- the key and the nonce associated.
+initialize :: ByteArrayAccess seed
+           => seed        -- ^ 40 bytes of seed
+           -> ChaChaDRG   -- ^ the initial ChaCha state
+initialize seed = ChaChaDRG $ C.initializeSimple seed
+
+-- | Initialize a new ChaCha context from 5-tuple of words64.
+-- This interface is useful when creating a RNG out of tests generators (e.g. QuickCheck).
+initializeWords :: (Word64, Word64, Word64, Word64, Word64) -> ChaChaDRG
+initializeWords (a,b,c,d,e) = initialize (B.allocAndFreeze 40 fill :: ScrubbedBytes)
+  where fill s = mapM_ (uncurry (pokeElemOff s)) [(0,a), (1,b), (2,c), (3,d), (4,e)]
+
+generate :: ByteArray output => Int -> ChaChaDRG -> (output, ChaChaDRG)
+generate nbBytes st@(ChaChaDRG prevSt)
+    | nbBytes <= 0 = (B.empty, st)
+    | otherwise    = let (output, newSt) = C.generateSimple prevSt nbBytes in (output, ChaChaDRG newSt)