Warn about instances exposing internals

Crypto/Cipher/RC4.hs

@@ -30,6 +30,11 @@ import           Crypto.Internal.Compat
 import           Crypto.Internal.Imports
 
 -- | The encryption state for RC4
+--
+-- This type is an instance of 'ByteArrayAccess' for debugging purpose. Internal
+-- layout is architecture dependent, may contain uninitialized data fragments,
+-- and change in future versions.  The bytearray should not be used as input to
+-- cryptographic algorithms.
 newtype State = State ScrubbedBytes
     deriving (ByteArrayAccess,NFData)
 

Crypto/Hash/IO.hs

@@ -24,6 +24,11 @@ import qualified Crypto.Internal.ByteArray as B
 import           Foreign.Ptr
 
 -- | A Mutable hash context
+--
+-- This type is an instance of 'B.ByteArrayAccess' for debugging purpose.
+-- Internal layout is architecture dependent, may contain uninitialized data
+-- fragments, and change in future versions.  The bytearray should not be used
+-- as input to cryptographic algorithms.
 newtype MutableContext a = MutableContext B.Bytes
     deriving (B.ByteArrayAccess)
 

Crypto/Hash/Types.hs

@@ -77,6 +77,11 @@ hashContextGetAlgorithm = undefined
 -}
 
 -- | Represent a context for a given hash algorithm.
+--
+-- This type is an instance of 'ByteArrayAccess' for debugging purpose. Internal
+-- layout is architecture dependent, may contain uninitialized data fragments,
+-- and change in future versions.  The bytearray should not be used as input to
+-- cryptographic algorithms.
 newtype Context a = Context Bytes
     deriving (ByteArrayAccess,NFData)
 

Crypto/MAC/Poly1305.hs

@@ -33,6 +33,11 @@ import           Crypto.Internal.DeepSeq
 import           Crypto.Error
 
 -- | Poly1305 State
+--
+-- This type is an instance of 'ByteArrayAccess' for debugging purpose. Internal
+-- layout is architecture dependent, may contain uninitialized data fragments,
+-- and change in future versions.  The bytearray should not be used as input to
+-- cryptographic algorithms.
 newtype State = State ScrubbedBytes
     deriving (ByteArrayAccess)