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{-# LANGUAGE ScopedTypeVariables #-}
module Foreign.Ptr.ConstantTimeEquals where
import Foreign (Ptr)
import Foreign.C.Types
foreign import ccall "openssl/mem.h CRYPTO_memcmp"
cryptoMemcmp :: Ptr a -> Ptr a -> CSize -> IO CInt
-- | Directly compares two buffers for equality. This operation takes an amount
-- of time dependent on the specified size but independent of either buffer's
-- contents.
constantTimeEquals :: Ptr a -> Ptr a -> Int -> IO Bool
constantTimeEquals a b size =
let size' = fromIntegral size :: CSize
in (== 0) <$> cryptoMemcmp a b size'
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