pbkdf

commit 93af1a1af0ed7731c953ef4c415f05c1401bc094
parent 503902b710af487d85b6bae2792f6c240b85abe3
Author: Jared Tobin <jared@jtobin.io>
Date:   Wed, 11 Jun 2025 11:49:26 +0400

lib: total functions

Diffstat:
M
README.md
 | 
2
+-
M
lib/Crypto/KDF/PBKDF.hs
 | 
14
+++++++-------
M
test/Main.hs
 | 
19
+++++++------------

3 files changed, 15 insertions(+), 20 deletions(-)
diff --git a/README.md b/README.md
@@ -21,7 +21,7 @@ A sample GHCi session:
   >
   > -- derive a 32-byte key from a secret
   > KDF.derive SHA256.hmac "my password" "my salt" 100 32
-  "\"\NAKqxp\165S\t\212i\139\SUB(\132\176\204\224<\164\177\144\&1D\209\175\145\139[K\159h\205"
+  Just "\"\NAKqxp\165S\t\212i\139\SUB(\132\176\204\224<\164\177\144\&1D\209\175\145\139[K\159h\205"
 ```
 
 ## Documentation
diff --git a/lib/Crypto/KDF/PBKDF.hs b/lib/Crypto/KDF/PBKDF.hs
@@ -21,6 +21,7 @@ module Crypto.KDF.PBKDF (
   , derive
   )where
 
+import Control.Monad (guard)
 import Data.Bits ((.>>.), (.&.))
 import qualified Data.Bits as B
 import qualified Data.ByteString as BS
@@ -70,7 +71,8 @@ xor = BS.packZipWith B.xor
 --   >>> import qualified Crypto.Hash.SHA256 as SHA256
 --   >>> import qualified Data.ByteString as BS
 --   >>> import qualified Data.ByteString.Base16 as B16
---   >>> BS.take 16 (B16.encode (derive SHA256.hmac "passwd" "salt" 1 64))
+--   >>> let Just key = derive SHA256.hmac "passwd" "salt" 1 64
+--   >>> BS.take 16 (B16.encode key)
 --   "55ac046e56e3089f"
 derive
   :: HMAC          -- ^ pseudo-random function (HMAC)
@@ -78,12 +80,10 @@ derive
   -> BS.ByteString -- ^ salt
   -> Word64        -- ^ iteration count
   -> Word32        -- ^ bytelength of derived key (max 0xffff_ffff * hlen)
-  -> BS.ByteString -- ^ derived key
-derive prf p s c dklen
-    | dklen > 0xffff_ffff * fi hlen =      -- 2 ^ 32 - 1
-        error "ppad-pbkdf (derive): derived key too long"
-    | otherwise =
-        loop mempty 1
+  -> Maybe BS.ByteString -- ^ derived key
+derive prf p s c dklen = do
+    guard (dklen <= 0xffff_ffff * fi hlen)
+    pure (loop mempty 1)
   where
     !hlen = BS.length (prf mempty mempty)
     !l = ceiling (fi dklen / fi hlen :: Double) :: Word32
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.PBKDF as KDF
-import qualified Data.ByteString as BS
 import qualified Data.Aeson as A
 import qualified Data.Text.IO as TIO
 import Test.Tasty
@@ -48,16 +46,13 @@ execute h W.PbkdfTest {..} = testCase t_msg $ do
         cow = pt_iterationCount
         siz = pt_dkLen
         pec = pt_dk
-    if   pt_result == "invalid"
-    then do
-      out <- try (pure $! KDF.derive hmac pas sal cow siz)
-               :: 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 pas sal cow siz
-      assertEqual mempty pec out
+    case KDF.derive hmac pas sal cow siz of
+      Nothing
+        | pt_result == "invalid" -> assertBool "invalid" True
+        | otherwise -> assertFailure mempty
+      Just out
+        | pt_result == "invalid" -> assertBool "invalid" (pec /= out)
+        | otherwise -> assertEqual mempty pec out
   where
     hmac = case h of
       SHA256 -> SHA256.hmac