hkdf

commit 5c310fb56f6a605581274343714bb3fd9bf00cee
parent caeb2c6cf101ee2dac766f849f3ea12a5e3f1c4a
Author: Jared Tobin <jared@jtobin.io>
Date:   Fri, 10 Jan 2025 14:54:50 +0400

lib: hkdf indexing/overflow fixes

Diffstat:
M
lib/Crypto/KDF/HMAC.hs
 | 
6
+++---

1 file changed, 3 insertions(+), 3 deletions(-)
diff --git a/lib/Crypto/KDF/HMAC.hs b/lib/Crypto/KDF/HMAC.hs
@@ -65,13 +65,13 @@ expand
   -> 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 0 mempty mempty)
+    | otherwise = BS.take len (go (1 :: Int) mempty mempty)
   where
     n = ceiling ((fi len :: Double) / (fi hashlen :: Double)) :: Int
     go !j t !tl
-      | j == fi n = BS.toStrict (BSB.toLazyByteString t)
+      | j > fi n = BS.toStrict (BSB.toLazyByteString t)
       | otherwise =
-          let nt = hmac prk (tl <> info <> BS.singleton j)
+          let nt = hmac prk (tl <> info <> BS.singleton (fi j))
           in  go (succ j) (t <> BSB.byteString nt) nt
 
 -- | HMAC-based key derivation function.