[ChaCha] only required byteArrayAccess and add a way to convert from binary

Crypto/Error/Types.hs

@@ -28,6 +28,7 @@ data CryptoError =
     -- symmetric cipher errors
       CryptoError_KeySizeInvalid
     | CryptoError_IvSizeInvalid
+    | CryptoError_SeedSizeInvalid
     | CryptoError_AEADModeNotSupported
     -- public key cryptography error
     | CryptoError_SecretKeySizeInvalid

Crypto/Random.hs

@@ -16,6 +16,7 @@ module Crypto.Random
     , seedNew
     , seedFromInteger
     , seedToInteger
+    , seedFromBinary
     -- * Deterministic Random class
     , getSystemDRG
     , drgNew
@@ -29,10 +30,12 @@ module Crypto.Random
     , MonadPseudoRandom
     ) where
 
+import Crypto.Error
 import Crypto.Random.Types
 import Crypto.Random.ChaChaDRG
 import Crypto.Random.SystemDRG
 import Data.ByteArray (ByteArray, ByteArrayAccess, ScrubbedBytes)
+import qualified Data.ByteArray as B
 import Crypto.Internal.Imports
 
 import qualified Crypto.Number.Serialize as Serialize
@@ -56,6 +59,12 @@ seedToInteger (Seed b) = Serialize.os2ip b
 seedFromInteger :: Integer -> Seed
 seedFromInteger i = Seed $ Serialize.i2ospOf_ seedLength (i `mod` 2^(seedLength * 8))
 
+-- | Convert a binary to a seed
+seedFromBinary :: ByteArrayAccess b => b -> CryptoFailable Seed
+seedFromBinary b
+    | B.length b /= 40 = CryptoFailed (CryptoError_SeedSizeInvalid)
+    | otherwise        = CryptoPassed $ Seed $ B.convert b
+
 -- | Create a new DRG from system entropy
 drgNew :: MonadRandom randomly => randomly ChaChaDRG
 drgNew = drgNewSeed `fmap` seedNew

Crypto/Random/ChaChaDRG.hs

@@ -14,7 +14,7 @@ module Crypto.Random.ChaChaDRG
 
 import           Crypto.Random.Types
 import           Crypto.Internal.Imports
-import           Crypto.Internal.ByteArray (ByteArray, ScrubbedBytes)
+import           Crypto.Internal.ByteArray (ByteArray, ByteArrayAccess, ScrubbedBytes)
 import qualified Crypto.Internal.ByteArray as B
 import           Foreign.Storable (pokeElemOff)
 
@@ -29,7 +29,7 @@ newtype ChaChaDRG = ChaChaDRG C.StateSimple
 
 -- | Initialize a new ChaCha context with the number of rounds,
 -- the key and the nonce associated.
-initialize :: ByteArray seed
+initialize :: B.ByteArrayAccess seed
            => seed        -- ^ 40 bytes of seed
            -> ChaChaDRG   -- ^ the initial ChaCha state
 initialize seed = ChaChaDRG $ C.initializeSimple seed