From ac77a20c067a63e3b03488abbc0caaf35495cbcc Mon Sep 17 00:00:00 2001
From: Vincent Hanquez <vincent@snarc.org>
Date: Fri, 3 Apr 2015 07:27:44 +0100
Subject: [PATCH] add simple ChaChaRNG

---
 Crypto/Random/ChaChaDRG.hs | 44 ++++++++++++++++++++++++++++++++++++++
 cryptonite.cabal           |  1 +
 2 files changed, 45 insertions(+)
 create mode 100644 Crypto/Random/ChaChaDRG.hs

diff --git a/Crypto/Random/ChaChaDRG.hs b/Crypto/Random/ChaChaDRG.hs
new file mode 100644
index 0000000..0d1999c
--- /dev/null
+++ b/Crypto/Random/ChaChaDRG.hs
@@ -0,0 +1,44 @@
+-- |
+-- Module      : Crypto.Random.ChaChaDRG
+-- License     : BSD-style
+-- Maintainer  : Vincent Hanquez <vincent@snarc.org>
+-- Stability   : stable
+-- Portability : good
+--
+module Crypto.Random.ChaChaDRG
+    ( ChaChaDRG
+    , initialize
+    , initializeWords
+    ) where
+
+import Crypto.Random.Types
+import Crypto.Internal.ByteArray
+import Data.SecureMem
+import Data.Word
+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
+
+-- | Initialize a new ChaCha context with the number of rounds,
+-- the key and the nonce associated.
+initialize :: ByteArray 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 (byteArrayAllocAndFreeze 40 fill :: SecureMem)
+  where fill s = mapM_ (uncurry (pokeElemOff s)) [(0,a), (1,b), (2,c), (3,d), (4,e)]
+
+generate :: ByteArray byteArray => Int -> ChaChaDRG -> (byteArray, ChaChaDRG)
+generate nbBytes st@(ChaChaDRG prevSt)
+    | nbBytes <= 0 = (empty, st)
+    | otherwise    = let (output, newSt) = C.generateSimple prevSt nbBytes in (output, ChaChaDRG newSt)
diff --git a/cryptonite.cabal b/cryptonite.cabal
index 0b714d0..72bff6a 100644
--- a/cryptonite.cabal
+++ b/cryptonite.cabal
@@ -84,6 +84,7 @@ Library
                      Crypto.Hash.Internal.Whirlpool
                      Crypto.Random.Entropy.Source
                      Crypto.Random.Entropy.Backend
+                     Crypto.Random.ChaChaDRG
                      Crypto.Internal.Compat
                      Crypto.Internal.Bytes
                      Crypto.Internal.ByteArray