Update tutorial based on suggestions

Crypto/Tutorial.hs

@@ -1,12 +1,12 @@
 
-{- How to use @cryptonite@ with symmetric block ciphers
+{- How to use @cryptonite@ with symmetric block ciphers 
 
 > {-# LANGUAGE OverloadedStrings #-}
 > {-# LANGUAGE ScopedTypeVariables #-}
 > {-# LANGUAGE GADTs #-}
 > 
 > import           Crypto.Cipher.AES (AES256)
-> import           Crypto.Cipher.Types (BlockCipher(..), Cipher(..), nullIV, KeySizeSpecifier(..))
+> import           Crypto.Cipher.Types (BlockCipher(..), Cipher(..), nullIV, KeySizeSpecifier(..), IV, makeIV)
 > import           Crypto.Error (CryptoFailable(..), CryptoError(..))
 > 
 > import qualified Crypto.Random.Types as CRT
@@ -18,40 +18,47 @@
 > data Key c a where
 >   Key :: (BlockCipher c, ByteArray a) => a -> Key c a 
 > 
-> genPrivateKey :: forall m c a. (CRT.MonadRandom m, BlockCipher c, ByteArray a) 
+> -- | Generates a string of bytes (key) of a specific length for a given block cipher 
->               => c -> m (Key c a) 
+> genSecretKey :: forall m c a. (CRT.MonadRandom m, BlockCipher c, ByteArray a) => c -> Int -> m (Key c a) 
-> genPrivateKey _ = fmap Key $ CRT.getRandomBytes $
+> genSecretKey _ = fmap Key . CRT.getRandomBytes 
->   case cipherKeySize (undefined :: c) of
+>   
->     KeySizeRange _ maxSize -> maxSize 
+> -- | Generate a random initialization vector for a given block cipher
->     KeySizeFixed ks -> ks 
+> genRandomIV :: forall m c. (CRT.MonadRandom m, BlockCipher c) => c -> m (Maybe (IV c)) 
->     KeySizeEnum [] -> error "No key size specified"
+> genRandomIV _ = do
->     KeySizeEnum kss -> last kss -- largest key size
+>   bytes :: ByteString <- CRT.getRandomBytes $ blockSize (undefined :: c) 
->     
+>   return $ makeIV bytes 
+> 
+> -- | Initialize a block cipher
 > initCipher :: (BlockCipher c, ByteArray a) => Key c a -> Either CryptoError c
 > initCipher (Key k) = case cipherInit k of
 >   CryptoFailed e -> Left e
 >   CryptoPassed a -> Right a
 > 
-> encrypt :: (BlockCipher c, ByteArray a) => Key c a -> a -> Either CryptoError a
+> encrypt :: (BlockCipher c, ByteArray a) => Key c a -> IV c -> a -> Either CryptoError a
-> encrypt privKey msg = 
+> encrypt secretKey initIV msg = 
->   case initCipher privKey of
+>   case initCipher secretKey of
 >     Left e -> Left e
->     Right c -> Right $ ctrCombine c nullIV msg
+>     Right c -> Right $ ctrCombine c initIV msg
 >     
-> decrypt :: (BlockCipher c, ByteArray a) => Key c a -> a -> Either CryptoError a 
+> decrypt :: (BlockCipher c, ByteArray a) => Key c a -> IV c -> a -> Either CryptoError a 
 > decrypt = encrypt
 > 
 > exampleAES256 :: ByteString -> IO ()
 > exampleAES256 msg = do
->   privKey <- genPrivateKey (undefined :: AES256)
+>   -- secret key needs 256 bits (32 * 8) 
->   let eMsg = encrypt privKey msg >>= decrypt privKey
+>   secretKey <- genSecretKey (undefined :: AES256) 32
->   case eMsg of
+>   mInitIV <- genRandomIV (undefined :: AES256) 
->     Left err -> error $ show err
+>   case mInitIV of
->     Right msg' -> do
+>     Nothing -> error "Failed to generate and initialization vector."
->       putStrLn $ "Original Message: " ++ show msg
+>     Just initIV -> do
->       putStrLn $ "Message after encryption & decryption: " ++ show msg'
+>       let encryptedMsg = encrypt secretKey initIV msg
->
+>           decryptedMsg = decrypt secretKey initIV =<< encryptedMsg
-> -- | More Examples... ?
+>       case (,) <$> encryptedMsg <*> decryptedMsg of
+>         Left err -> error $ show err
+>         Right (eMsg, dMsg) -> do
+>           putStrLn $ "Original Message: " ++ show msg
+>           putStrLn $ "Message after encryption: " ++ show eMsg 
+>           putStrLn $ "Message after decryption: " ++ show dMsg
 
 |-}