It's short, so I'll post it here. Any comments? Thanks, -Yitz module DevRandom where import System.IO import System.IO.Error import Foreign.Marshal.Alloc import Foreign.Storable import Foreign.Ptr data BlockingMode = Blocking | NonBlocking deriving (Eq, Show) -- Read data from the system random device. -- Return Nothing if there is currently not -- enough entropy in the system random device. devRandom :: Storable a => IO (Maybe a) devRandom = readDev "/dev/random" NonBlocking -- Read data from the system random device. -- If necessary, wait until there is -- enough entropy in the system random device. devRandomWait :: Storable a => IO a devRandomWait = readDev dev Blocking >>= maybe (devRandomError dev) return where dev = "/dev/random" -- Read data from the system random device. -- If there is currently not enough entropy -- in the system random device, use a lower -- quality source of randomness instead. devURandom :: Storable a => IO a devURandom = readDev dev NonBlocking >>= maybe (devRandomError dev) return where dev = "/dev/urandom" readDev :: Storable a => FilePath -> BlockingMode -> IO (Maybe a) readDev dev mode = do h <- openFile dev ReadMode hSetBuffering h NoBuffering alloca $ getMaybe h undefined where getMaybe :: Storable a => Handle -> a -> Ptr a -> IO (Maybe a) getMaybe h undef ptr = do let size = sizeOf undef n <- case mode of Blocking -> hGetBuf h ptr size NonBlocking -> hGetBufNonBlocking h ptr size if n < size then return Nothing else peek ptr >>= return . Just devRandomError :: FilePath -> IO a devRandomError p = ioError $ mkIOError illegalOperationErrorType "Unable to read from the system random device" Nothing (Just p)