Fix padding

cryptoids/changes.md

@@ -1,3 +1,7 @@
+# 0.3.0.0
+    - Better exception type (does no longer leak private information)
+    - 'Data.CryptoID.Poly' now supports padding the plaintext to a certain length before encryption
+
 # 0.2.0.0
     - Rename 'Data.CryptoID.Poly' to 'Data.CryptoID.ByteString'
     - Introduce 'Data.CryptoID.Poly' doing actual serialization
@@ -12,3 +16,4 @@
 # 0.0.0
 
 First published version
+

cryptoids/cryptoids.cabal

@@ -1,5 +1,5 @@
 name:                cryptoids
-version:             0.2.0.0
+version:             0.3.0.0
 synopsis:            Reversable and secure encoding of object ids as a bytestring
 license:             BSD3
 license-file:        LICENSE

cryptoids/src/Data/CryptoID/ByteString.hs

@@ -29,6 +29,7 @@ import Data.Binary.Put
 import Data.Binary.Get
 
 import Data.ByteString (ByteString)
+import qualified Data.ByteString as ByteString
 import qualified Data.ByteString.Char8 as ByteString.Char
 
 import qualified Data.ByteString.Lazy as Lazy (ByteString)
@@ -100,10 +101,19 @@ instance Binary CryptoIDKey where
 
 
 -- | Error cases that can be encountered during 'encrypt' and 'decrypt'
+--
+-- Care has been taken to ensure that presenting values of 'CryptoIDError' to an
+-- attacker leaks no plaintext (it does leak information about the length of the
+-- plaintext).
 data CryptoIDError
   = AlgorithmError CryptoError
     -- ^ One of the underlying cryptographic algorithms
     --   ('CryptoHash' or 'CryptoCipher') failed.
+  | PlaintextIsWrongLength Int
+    -- ^ The length of the plaintext is not a multiple of the block size of
+    --   'CryptoCipher'
+    --
+    -- The length of the offending plaintext is included.
   | NamespaceHashIsWrongLength ByteString
     -- ^ The length of the digest produced by 'CryptoHash' does
     --   not match the block size of 'CryptoCipher'.
@@ -112,10 +122,12 @@ data CryptoIDError
     --
     -- This error should not occur and is included primarily
     -- for sake of totality.
-  | CiphertextConversionFailed
-    -- ^ The produced 'ByteString' is the wrong length for conversion into a
-    --   ciphertext.
-  | DeserializationError (Lazy.ByteString, ByteOffset, String)
+  | CiphertextConversionFailed ByteString
+    -- ^ The produced 'ByteString' is the wrong length for deserialization into
+    --   a ciphertext.
+    --
+    -- The offending 'ByteString' is included.
+  | DeserializationError
     -- ^ The plaintext obtained by decrypting a ciphertext with the given
     --   'CryptoIDKey' in the context of the @namespace@ could not be
     --   deserialized into a value of the expected @payload@-type.
@@ -183,8 +195,8 @@ encrypt :: forall m namespace.
 encrypt (keyMaterial -> key) plaintext = do
   cipher <- cryptoFailable (cipherInit key :: CryptoFailable CryptoCipher)
   namespace <- namespace' (Proxy :: Proxy namespace)
-  when (ByteArray.length plaintext `mod` blockSize cipher /= 0) $
-    throwM CiphertextConversionFailed
+  when (ByteString.length plaintext `mod` blockSize cipher /= 0) $
+    throwM . PlaintextIsWrongLength $ ByteString.length plaintext
   return . CryptoID $ cbcEncrypt cipher namespace plaintext
 
 

cryptoids/src/Data/CryptoID/Poly.hs

@@ -33,11 +33,15 @@ import qualified Data.CryptoID.ByteString as ByteString (encrypt, decrypt)
 
 import Data.Binary
 
+import Data.Monoid
+
 import Data.ByteString (ByteString)
+import qualified Data.ByteString as ByteString
 import qualified Data.ByteString.Lazy as Lazy.ByteString
 
 import GHC.TypeLits
 
+import Control.Monad
 import Control.Monad.Catch (MonadThrow(..))
   
 
@@ -50,10 +54,22 @@ encrypt :: forall a m c namespace.
            ( KnownSymbol namespace
            , MonadThrow m
            , Binary a
-           ) => (ByteString -> m c) -> CryptoIDKey -> a -> m (CryptoID namespace c)
-encrypt encode' key plaintext = do
-  cID <- ByteString.encrypt key . Lazy.ByteString.toStrict $ encode plaintext
+           ) => Maybe Int -- ^ Ensure the resulting ciphertext is of this size (needs to be a multiple of the block size of 'CryptoCipher' in bytes, otherwise an exception will be thrown at runtime)
+        -> (ByteString -> m c)
+        -> CryptoIDKey
+        -> a
+        -> m (CryptoID namespace c)
+encrypt pLength encode' key plaintext = do
+  cID <- ByteString.encrypt key <=< pad . Lazy.ByteString.toStrict $ encode plaintext
   _ciphertext encode' cID
+  where
+    pad str
+      | Just l <- pLength
+      , l' <= l           = return $ str <> ByteString.replicate (l - l') 0
+      | Just _ <- pLength = throwM $ CiphertextConversionFailed str
+      | otherwise         = return str
+      where
+        l' = ByteString.length str
 
 
 -- | Decrypt a serialized value
@@ -67,7 +83,7 @@ decrypt decode key cID = do
   plaintext <- Lazy.ByteString.fromStrict <$> ByteString.decrypt key cID'
 
   case decodeOrFail plaintext of
-    Left err -> throwM $ DeserializationError err
+    Left _ -> throwM DeserializationError
     Right (rem, _, res)
       | Lazy.ByteString.all (== 0) rem -> return res
       | otherwise -> throwM InvalidNamespaceDetected

uuid-crypto/changes.md

@@ -1,3 +1,6 @@
+# 1.2.0.0
+    - Pad plaintext before encryption, allowing encryption of payloads shorter than 128 bits
+
 # 1.1.1.0
     - Switch to using the new 'Data.CryptoID.Poly'
 

uuid-crypto/src/Data/UUID/Cryptographic.hs

@@ -53,7 +53,7 @@ encrypt :: forall a m namespace.
            , Binary a
            , MonadThrow m
            ) => CryptoIDKey -> a -> m (CryptoUUID namespace)
-encrypt = Poly.encrypt $ maybe (throwM CiphertextConversionFailed) return . fromByteString . Lazy.ByteString.fromStrict
+encrypt = Poly.encrypt (Just 16) $ \str -> maybe (throwM $ CiphertextConversionFailed str) return . fromByteString $ Lazy.ByteString.fromStrict str
 
 
 -- | Decrypt an arbitrary serializable value
@@ -68,7 +68,7 @@ decrypt :: forall a m namespace.
            ) => CryptoIDKey -> CryptoUUID namespace -> m a
 decrypt = Poly.decrypt $ check . decodeOrFail . toByteString
   where
-    check (Left err) = throwM $ DeserializationError err
+    check (Left _) = throwM DeserializationError
     check (Right (rem, _, res))
       | Lazy.ByteString.all (== 0) rem = return res
       | otherwise = throwM InvalidNamespaceDetected

uuid-crypto/uuid-crypto.cabal

@@ -1,5 +1,5 @@
 name:                uuid-crypto
-version:             1.1.1.0
+version:             1.2.0.0
 synopsis:            Reversable and secure encoding of object ids as uuids
 license:             BSD3
 license-file:        LICENSE
@@ -28,7 +28,7 @@ library
   other-extensions:    ScopedTypeVariables
   build-depends:       base            >=4.9      && <4.11
                      , cryptoids-types ==0.0.0
-                     , cryptoids       ==0.2.0.*
+                     , cryptoids       ==0.3.0.*
                      , uuid            >=1.3.13   && <1.4
                      , binary          >=0.8.3.0  && <0.9
                      , bytestring      >=0.10.8.1 && <0.11