clean up read/show abuse

Avoid ever using read to parse a non-haskell formatted input string.

show :: Key is arguably still show abuse, but displaying Keys as filenames
is just too useful to give up.

Types/Crypto.hs

@@ -7,17 +7,9 @@
 
 module Types.Crypto where
 
-import Data.String.Utils
-
 -- XXX ideally, this would be a locked memory region
 newtype Cipher = Cipher String
 
 data EncryptedCipher = EncryptedCipher String KeyIds
 
 newtype KeyIds = KeyIds [String]
-
-instance Show KeyIds where
-	show (KeyIds ks) = join "," ks
-
-instance Read KeyIds where
-	readsPrec _ s = [(KeyIds (split "," s), "")]