From 0bb8daa7da52240a971a4ce83d97cfb62971ea78 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Roman=20Smr=C5=BE?= <roman.smrz@seznam.cz>
Date: Sun, 18 Oct 2026 16:52:41 +0200
Subject: Add crypto backend using various reference libraries

---
 src/crypto/reflibs/Crypto/PubKey/Curve25519.hs | 84 ++++++++++++++++++++++++++
 1 file changed, 84 insertions(+)
 create mode 100644 src/crypto/reflibs/Crypto/PubKey/Curve25519.hs

(limited to 'src/crypto/reflibs/Crypto/PubKey/Curve25519.hs')

diff --git a/src/crypto/reflibs/Crypto/PubKey/Curve25519.hs b/src/crypto/reflibs/Crypto/PubKey/Curve25519.hs
new file mode 100644
index 0000000..ea8e035
--- /dev/null
+++ b/src/crypto/reflibs/Crypto/PubKey/Curve25519.hs
@@ -0,0 +1,84 @@
+module Crypto.PubKey.Curve25519 (
+    CxSecretKey,
+    CxPublicKey,
+    DhSecret,
+
+    cxSecretKey,
+    cxPublicKey,
+
+    cxGenerateSecretKey,
+    cxToPublic,
+    diffieHellman,
+) where
+
+import Control.Monad
+
+import Crypto.Error
+import Crypto.Random
+
+import Data.Bits
+import Data.ByteArray
+import Data.ByteString (ByteString)
+import Data.ByteString qualified as BS
+import Data.ByteString.Unsafe qualified as BS
+import Data.Word
+
+import Foreign.C.Types
+import Foreign.Marshal.Alloc
+import Foreign.Marshal.Utils
+import Foreign.Ptr
+import Foreign.Storable
+
+import System.IO.Unsafe
+
+
+newtype CxSecretKey = CxSecretKey ByteString
+    deriving (Eq, ByteArrayAccess)
+
+newtype CxPublicKey = CxPublicKey ByteString
+    deriving (Eq, Show, ByteArrayAccess)
+
+newtype DhSecret = DhSecret ByteString
+    deriving (Eq, Show, ByteArrayAccess)
+
+cxSecretKey :: ByteArrayAccess bs => bs -> CryptoFailable CxSecretKey
+cxSecretKey ba
+    | BS.length bs == 32 = CryptoPassed $ CxSecretKey bs
+    | otherwise = CryptoFailed CryptoError
+  where
+    bs = convert ba
+
+cxPublicKey :: ByteString -> CryptoFailable CxPublicKey
+cxPublicKey bs
+    | BS.length bs == 32 = CryptoPassed $ CxPublicKey bs
+    | otherwise = CryptoFailed CryptoError
+
+cxGenerateSecretKey :: IO CxSecretKey
+cxGenerateSecretKey = do
+    bs <- getRandomBytes 32
+    BS.unsafeUseAsCString bs $ \ptr -> do
+        pokeElemOff ptr 0 . (.&. 248) =<< peekElemOff ptr 0
+        pokeElemOff ptr 31 . (.|. 64) . (.&. 127) =<< peekElemOff ptr 31
+    return $ CxSecretKey bs
+
+cxToPublic :: CxSecretKey -> CxPublicKey
+cxToPublic (CxSecretKey bs) = unsafePerformIO $ do
+    let len = 32
+    ptr <- mallocBytes len
+    BS.unsafeUseAsCString bs $ \secret -> do
+        allocaBytes 32 $ \basepoint -> do
+            fillBytes basepoint 0 len
+            pokeElemOff basepoint 0 9
+            void $ curve25519_donna ptr (castPtr secret) basepoint
+    CxPublicKey <$> BS.unsafePackCStringFinalizer ptr len (free ptr)
+
+diffieHellman :: CxPublicKey -> CxSecretKey -> DhSecret
+diffieHellman (CxPublicKey bpub) (CxSecretKey bsec) = unsafePerformIO $ do
+    let len = 32
+    ptr <- mallocBytes len
+    BS.unsafeUseAsCString bpub $ \pub -> do
+        BS.unsafeUseAsCString bsec $ \sec -> do
+            void $ curve25519_donna ptr (castPtr sec) (castPtr pub)
+    DhSecret <$> BS.unsafePackCStringFinalizer ptr len (free ptr)
+
+foreign import ccall unsafe "curve25519_donna" curve25519_donna :: Ptr Word8 -> Ptr Word8 -> Ptr Word8 -> IO CInt
-- 
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