{-# LANGUAGE LambdaCase, ScopedTypeVariables #-}
{-

    Example of using PBKDF2 to seed the Multiply with Carry (MWC)
    random number generator with a string.

    Copyright 2015 Ken Takusagawa

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <http://www.gnu.org/licenses/>.

-}

module Main(main) where {
import qualified System.Random.MWC as MWC;
import Data.ByteString (ByteString);
import qualified Data.Binary as Binary;
import Data.Binary(Binary);
import Data.Binary.Get(runGet);
import qualified Data.Binary.Get as Binary.Get;
import Crypto.PBKDF.ByteString(sha512PBKDF2);
import Data.Text.Encoding(encodeUtf8);
import qualified Data.Text as Text;
import qualified Data.ByteString.Lazy as Lazy;
import qualified Data.Vector as Vector;
import Data.Word;

main :: IO ();
main = do {
gen <- MWC.initialize $ Vector.fromList $ runGet getManyUntilEmpty $ Lazy.fromStrict $ sha512PBKDF2 (string2bs mypassphrase) (string2bs salt) (fromIntegral iterations_pbkdf2) (fromIntegral keylength_bytes);
sequence_ $ repeat $ (MWC.uniform gen :: IO Word8) >>= print;
};

string2bs :: String -> ByteString;
string2bs = encodeUtf8 . Text.pack;

-- world's most famous password
mypassphrase :: String;
mypassphrase = "ACollectionOfDiplomaticHistorySince_1966_ToThe_PresentDay#";

salt::String;
salt = "mysalt98754321";

-- magic number for mwc
mwc_statesize :: Integer;
mwc_statesize = 258;

keylength_bytes :: Integer;
keylength_bytes = mwc_statesize * 4;

-- MWC is not a cryptographically secure generator, so it would be
-- pointless to harden against brute-force key-recovery attacks by
-- having a high number of iterations.
iterations_pbkdf2 :: Integer;
iterations_pbkdf2 = 1;

-- A seemingly useful function for Binary.Get but unfortunately of
-- limited use, because it does not parse lazily, i.e. does not return
-- a lazy list; it must consume the entire input before returning the
-- first item.
getManyUntilEmpty :: forall a. Binary a => Binary.Get [a];
getManyUntilEmpty = Binary.Get.isEmpty >>= \case {
True -> return [];
False -> do {
x <- Binary.get;
rest :: [a] <- getManyUntilEmpty;
return $ x:rest;
}};


} -- end