htools: add a small module for crypto functions

This adds a dependency on the following new libraries:

- Data.HMAC module from the 'crypto' library
- Data.Text from the 'text' library
- Data.ByteString from the 'bytestring' library

In Debian, the bytestring library comes with the ghc compiler, whereas
the other two are available separately in wheezy/unstable.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>

Makefile.am

@@ -397,6 +397,7 @@ HS_LIB_SRCS = \
 	htools/Ganeti/BasicTypes.hs \
 	htools/Ganeti/Confd.hs \
 	htools/Ganeti/Config.hs \
+	htools/Ganeti/Hash.hs \
 	htools/Ganeti/Jobs.hs \
 	htools/Ganeti/Luxi.hs \
 	htools/Ganeti/Objects.hs \

htools/Ganeti/Hash.hs

+{-| Crypto-related helper functions.
+
+-}
+
+{-
+
+Copyright (C) 2011, 2012 Google Inc.
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful, but
+WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program; if not, write to the Free Software
+Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
+02110-1301, USA.
+
+-}
+
+module Ganeti.Hash
+  ( computeMac
+  , verifyMac
+  , HashKey
+  ) where
+
+import qualified Data.ByteString as B
+import Data.Char
+import Data.HMAC (hmac_sha1)
+import qualified Data.Text as T
+import Data.Text.Encoding (encodeUtf8)
+import Data.Word
+import Text.Printf (printf)
+
+-- | Type alias for the hash key. This depends on the library being
+-- used.
+type HashKey = [Word8]
+
+-- | Converts a string to a list of bytes.
+stringToWord8 :: String -> HashKey
+stringToWord8 = B.unpack . encodeUtf8 . T.pack
+
+-- | Converts a list of bytes to a string.
+word8ToString :: HashKey -> String
+word8ToString = concat . map (printf "%02x")
+
+-- | Computes the HMAC for a given key/test and salt.
+computeMac :: HashKey -> Maybe String -> String -> String
+computeMac key salt text =
+  word8ToString . hmac_sha1 key . stringToWord8 $ maybe text (++ text) salt
+
+-- | Verifies the HMAC for a given message.
+verifyMac :: HashKey -> Maybe String -> String -> String -> Bool
+verifyMac key salt text digest =
+  map toLower digest == computeMac key salt text