From 2e7bd84469eba730f24dd3e448cca22f5aed16f4 Mon Sep 17 00:00:00 2001
From: Benjamin Barenblat <bbaren@google.com>
Date: Tue, 4 Sep 2018 18:29:34 -0400
Subject: Enable error checking for HKDF computations

---
 src/Codec/Crypto/HKDF.hs | 33 ++++++++++++++++++++-------------
 1 file changed, 20 insertions(+), 13 deletions(-)

(limited to 'src/Codec')

diff --git a/src/Codec/Crypto/HKDF.hs b/src/Codec/Crypto/HKDF.hs
index bc1ea61..31d0be3 100644
--- a/src/Codec/Crypto/HKDF.hs
+++ b/src/Codec/Crypto/HKDF.hs
@@ -48,16 +48,23 @@ module Codec.Crypto.HKDF
     -- to do so, specify the empty string as the associated data.
   , AssociatedData(AssociatedData)
 
+    -- * Error handling
+  , Error
+
     -- * Legacy functions
   , md5
   ) where
 
+import Control.Monad ((>=>))
+import Control.Monad.Trans.Class (lift)
+import Control.Monad.Trans.Except (runExceptT)
 import Foreign (allocaArray)
 import Foreign.Marshal.Unsafe (unsafeLocalState)
 
 import BTLS.BoringSSL.Digest (evpMaxMDSize)
 import BTLS.BoringSSL.HKDF
-import BTLS.Buffer (onBufferOfMaxSize, packCUStringLen)
+import BTLS.Buffer (onBufferOfMaxSize', packCUStringLen)
+import BTLS.Result (Error, check)
 import BTLS.Types
   ( Algorithm(Algorithm), AssociatedData(AssociatedData), Salt(Salt)
   , SecretKey(SecretKey), noSalt
@@ -66,7 +73,7 @@ import Data.Digest (md5, sha1, sha224, sha256, sha384, sha512)
 
 -- | Computes an HKDF. It is defined by
 --
--- prop> hkdf md salt info len = expand md info len . extract md salt
+-- prop> hkdf md salt info len = extract md salt >=> expand md info len
 --
 -- but may be faster than calling the two functions individually.
 hkdf ::
@@ -75,16 +82,16 @@ hkdf ::
   -> AssociatedData
   -> Int -- ^ The length of the derived key, in bytes.
   -> SecretKey
-  -> SecretKey
-hkdf md salt info outLen = expand md info outLen . extract md salt
+  -> Either [Error] SecretKey
+hkdf md salt info outLen = extract md salt >=> expand md info outLen
 
 -- | Computes an HKDF pseudorandom key (PRK).
-extract :: Algorithm -> Salt -> SecretKey -> SecretKey
+extract :: Algorithm -> Salt -> SecretKey -> Either [Error] SecretKey
 extract (Algorithm md) (Salt salt) (SecretKey secret) =
-  SecretKey $
+  fmap SecretKey $
     unsafeLocalState $
-      onBufferOfMaxSize evpMaxMDSize $ \pOutKey pOutLen -> do
-        hkdfExtract pOutKey pOutLen md secret salt
+      onBufferOfMaxSize' evpMaxMDSize $ \pOutKey pOutLen ->
+        check $ hkdfExtract pOutKey pOutLen md secret salt
 
 -- | Computes HKDF output key material (OKM).
 expand ::
@@ -92,10 +99,10 @@ expand ::
   -> AssociatedData
   -> Int -- ^ The length of the OKM, in bytes.
   -> SecretKey
-  -> SecretKey
+  -> Either [Error] SecretKey
 expand (Algorithm md) (AssociatedData info) outLen (SecretKey secret) =
-  SecretKey $
+  fmap SecretKey $
     unsafeLocalState $
-      allocaArray outLen $ \pOutKey -> do
-        hkdfExpand pOutKey outLen md secret info
-        packCUStringLen (pOutKey, outLen)
+      allocaArray outLen $ \pOutKey -> runExceptT $ do
+        check $ hkdfExpand pOutKey outLen md secret info
+        lift $ packCUStringLen (pOutKey, outLen)
-- 
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