sha512

commit b7fff78e638b0b09f5c2b02650047641bea91918
parent c454a32a4a39b0e18601b8139a12ae895c9b631e
Author: Jared Tobin <jared@jtobin.io>
Date:   Sun,  6 Oct 2024 20:41:42 +0400

lib: hash long keys in hmac

Diffstat:
M
lib/Crypto/Hash/SHA512.hs
 | 
34
+++++++++++++++++++++++-----------

1 file changed, 23 insertions(+), 11 deletions(-)
diff --git a/lib/Crypto/Hash/SHA512.hs b/lib/Crypto/Hash/SHA512.hs
@@ -500,29 +500,41 @@ hash_lazy bl = cat (go iv (pad_lazy bl)) where
 --
 --   The 512-bit MAC is returned as a strict bytestring.
 --
+--   Per RFC 2104, the key /should/ be a minimum of 64 bytes long. Keys
+--   exceeding 1024 bytes in length will first be hashed (via SHA-512).
+--
 --   >>> hmac "strict bytestring key" "strict bytestring input"
 --   "<strict 512-bit MAC>"
 hmac :: BS.ByteString -> BS.ByteString -> BS.ByteString
 hmac k = hmac_lazy k . BL.fromStrict
 
+data KeyAndLen = KeyAndLen
+  {-# UNPACK #-} !BS.ByteString
+  {-# UNPACK #-} !Int
+
 -- | Produce a message authentication code for a lazy bytestring, based
 --   on the provided (strict, bytestring) key, via SHA-512.
 --
 --   The 512-bit MAC is returned as a strict bytestring.
 --
+--   Per RFC 2104, the key /should/ be a minimum of 64 bytes long. Keys
+--   exceeding 1024 bytes in length will first be hashed (via SHA-512).
+--
 --   >>> hmac_lazy "strict bytestring key" "lazy bytestring input"
 --   "<strict 512-bit MAC>"
 hmac_lazy :: BS.ByteString -> BL.ByteString -> BS.ByteString
-hmac_lazy k text
-    | lk > 128 = error "ppad-sha512: hmac key exceeds 128 bytes"
-    | otherwise =
-        let step1 = k <> BS.replicate (128 - lk) 0x00
-            step2 = BS.map (B.xor 0x36) step1
-            step3 = BL.fromStrict step2 <> text
-            step4 = hash_lazy step3
-            step5 = BS.map (B.xor 0x5C) step1
-            step6 = step5 <> step4
-        in  hash step6
+hmac_lazy mk text =
+    let step1 = k <> BS.replicate (128 - lk) 0x00
+        step2 = BS.map (B.xor 0x36) step1
+        step3 = BL.fromStrict step2 <> text
+        step4 = hash_lazy step3
+        step5 = BS.map (B.xor 0x5C) step1
+        step6 = step5 <> step4
+    in  hash step6
   where
-    lk = fi (BS.length k)
+    !(KeyAndLen k lk) =
+      let l = BS.length mk
+      in  if   l > 128
+          then KeyAndLen (hash mk) 64
+          else KeyAndLen mk l