hkdf

commit 93aaf3eafad677087ffbea6fc5c24a63cb9651ea
parent 3da63a199d294c6e7c4306786ea071c7f969f21d
Author: Jared Tobin <jared@jtobin.io>
Date:   Wed, 11 Jun 2025 11:41:35 +0400

lib: total functions

Diffstat:
M
README.md
 | 
2
+-
M
lib/Crypto/KDF/HMAC.hs
 | 
8
++++----
M
test/Main.hs
 | 
19
+++++++------------

3 files changed, 12 insertions(+), 17 deletions(-)
diff --git a/README.md b/README.md
@@ -20,7 +20,7 @@ A sample GHCi session:
   > import qualified Crypto.Hash.SHA256 as SHA256
   >
   > -- derive a 32-byte key from a secret
-  > KDF.derive SHA256.hmac "my salt" "my optional info" 32 "my secret input"
+  > Just (KDF.derive SHA256.hmac "my salt" "my optional info" 32 "my secret input")
   "\EM\232\v\140\202\230\f2:\221n\221\209\233\US\209>\174_!\138\255\\C\150\237^X\226\tt\252"
 ```
 
diff --git a/lib/Crypto/KDF/HMAC.hs b/lib/Crypto/KDF/HMAC.hs
@@ -66,10 +66,10 @@ expand
   -> BS.ByteString  -- ^ optional context and application-specific info
   -> Word64         -- ^ bytelength of output keying material
   -> BS.ByteString  -- ^ pseudorandom key
-  -> BS.ByteString  -- ^ output keying material
+  -> Maybe BS.ByteString  -- ^ output keying material
 expand (HMACEnv hmac hashlen) info (fi -> len) prk
-    | len > 255 * hashlen = error "ppad-hkdf (expand): invalid outlength"
-    | otherwise = BS.take len (go (1 :: Int) mempty mempty)
+    | len > 255 * hashlen = Nothing
+    | otherwise = pure (BS.take len (go (1 :: Int) mempty mempty))
   where
     n = ceiling ((fi len :: Double) / (fi hashlen :: Double)) :: Int
     go !j t !tl
@@ -95,7 +95,7 @@ derive
   -> BS.ByteString -- ^ optional context and application-specific info
   -> Word64        -- ^ bytelength of output keying material (<= 255 * hashlen)
   -> BS.ByteString -- ^ input keying material
-  -> BS.ByteString -- ^ output keying material
+  -> Maybe BS.ByteString -- ^ output keying material
 derive hmac salt info len = expand env info len . extract env salt where
   env = HMACEnv hmac (fi (BS.length (hmac mempty mempty)))
 
diff --git a/test/Main.hs b/test/Main.hs
@@ -3,11 +3,9 @@
 
 module Main where
 
-import Control.Exception
 import qualified Crypto.Hash.SHA256 as SHA256
 import qualified Crypto.Hash.SHA512 as SHA512
 import qualified Crypto.KDF.HMAC as KDF
-import qualified Data.ByteString as BS
 import qualified Data.Aeson as A
 import qualified Data.Text.IO as TIO
 import Test.Tasty
@@ -50,16 +48,13 @@ execute h W.HkdfTest {..} = testCase t_msg $ do
         inf = ht_info
         siz = ht_size
         pec = ht_okm
-    if   ht_result == "invalid"
-    then do
-      out <- try (pure $! KDF.derive hmac sal inf siz ikm)
-               :: IO (Either ErrorCall BS.ByteString)
-      case out of
-        Left _  -> assertBool "invalid" True
-        Right o -> assertBool "invalid" (pec /= o)
-    else do
-      let out = KDF.derive hmac sal inf siz ikm
-      assertEqual mempty pec out
+    case KDF.derive hmac sal inf siz ikm of
+      Nothing
+        | ht_result == "invalid" -> assertBool "invalid" True
+        | otherwise -> assertFailure "failed"
+      Just out
+        | ht_result == "invalid" -> assertBool "invalid" (pec /= out)
+        | otherwise -> assertEqual mempty pec out
   where
     hmac = case h of
       SHA256 -> SHA256.hmac