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authorGravatar Benjamin Barenblat <bbaren@google.com>2018-03-24 21:21:20 -0400
committerGravatar Benjamin Barenblat <bbaren@google.com>2018-03-24 21:21:20 -0400
commit7aeeadd0647bfa649b9af859fe5dd7b5cc52afe9 (patch)
tree82802ca134fccaff7a6824dd7d516aeae1b749a2 /src/Foreign/Ptr
parent0ed87caa3481cbb6f8c2e809e5ec7df6f6245406 (diff)
Implement HMAC
Diffstat (limited to 'src/Foreign/Ptr')
-rw-r--r--src/Foreign/Ptr/ConstantTimeEquals.hs17
1 files changed, 17 insertions, 0 deletions
diff --git a/src/Foreign/Ptr/ConstantTimeEquals.hs b/src/Foreign/Ptr/ConstantTimeEquals.hs
new file mode 100644
index 0000000..bb8d2d4
--- /dev/null
+++ b/src/Foreign/Ptr/ConstantTimeEquals.hs
@@ -0,0 +1,17 @@
+{-# 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'