content: {-| Crypto-related helper functions.
  
  -}
  
  {-
  
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  THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
  IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
  TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
  PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
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  -}
  
  module Ganeti.Hash
    ( computeMac
    , verifyMac
    , HashKey
    ) where
  
  import qualified Data.ByteString as B
  import qualified Data.ByteString.UTF8 as BU
  import Crypto.Hash.Algorithms
  import Crypto.MAC.HMAC
  import Data.Char
  import Data.Word
  
  -- | Type alias for the hash key. This depends on the library being
  -- used.
  type HashKey = [Word8]
  
  -- | Computes the HMAC for a given key/test and salt.
  computeMac :: HashKey -> Maybe String -> String -> String
  computeMac key salt text =
    let hashable = maybe text (++ text) salt
    in show . hmacGetDigest $
      (hmac (B.pack key) (BU.fromString hashable) :: HMAC SHA1)
  
  -- | 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
  