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diff --git a/Types/Crypto.hs b/Types/Crypto.hs
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+{- git-annex crypto types
+ -
+ - Copyright 2011-2012 Joey Hess <joey@kitenet.net>
+ -
+ - Licensed under the GNU GPL version 3 or higher.
+ -}
+
+module Types.Crypto (
+	Cipher(..),
+	StorableCipher(..),
+	EncryptedCipherVariant(..),
+	KeyIds(..),
+	Mac(..),
+	readMac,
+	showMac,
+	defaultMac,
+	calcMac,
+) where
+
+import qualified Data.ByteString.Lazy as L
+import Data.Digest.Pure.SHA
+
+import Utility.Gpg (KeyIds(..))
+
+-- XXX ideally, this would be a locked memory region
+data Cipher = Cipher String | MacOnlyCipher String
+
+data StorableCipher = EncryptedCipher String EncryptedCipherVariant KeyIds
+		| SharedCipher String
+	deriving (Ord, Eq)
+data EncryptedCipherVariant = Hybrid | PubKey
+	deriving (Ord, Eq)
+
+{- File names are (client-side) MAC'ed on special remotes.
+ - The chosen MAC algorithm needs to be same for all files stored on the
+ - remote.
+ -}
+data Mac = HmacSha1 | HmacSha224 | HmacSha256 | HmacSha384 | HmacSha512
+	deriving (Eq)
+
+defaultMac :: Mac
+defaultMac = HmacSha1
+
+-- MAC algorithms are shown as follows in the file names.
+showMac :: Mac -> String
+showMac HmacSha1   = "HMACSHA1"
+showMac HmacSha224 = "HMACSHA224"
+showMac HmacSha256 = "HMACSHA256"
+showMac HmacSha384 = "HMACSHA384"
+showMac HmacSha512 = "HMACSHA512"
+
+-- Read the MAC algorithm from the remote config.
+readMac :: String -> Maybe Mac
+readMac "HMACSHA1"   = Just HmacSha1
+readMac "HMACSHA224" = Just HmacSha224
+readMac "HMACSHA256" = Just HmacSha256
+readMac "HMACSHA384" = Just HmacSha384
+readMac "HMACSHA512" = Just HmacSha512
+readMac _ = Nothing
+
+calcMac
+  :: Mac	  -- ^ MAC
+  -> L.ByteString -- ^ secret key
+  -> L.ByteString -- ^ message
+  -> String	  -- ^ MAC'ed message, in hexadecimals
+calcMac mac = case mac of
+	HmacSha1   -> showDigest $* hmacSha1
+	HmacSha224 -> showDigest $* hmacSha224
+	HmacSha256 -> showDigest $* hmacSha256
+	HmacSha384 -> showDigest $* hmacSha384
+	HmacSha512 -> showDigest $* hmacSha512
+  where
+	($*) g f x y = g $ f x y