1 files changed, 174 insertions, 0 deletions
diff --git a/src/Erebos/Channel.hs b/src/Erebos/Channel.hs
new file mode 100644
index 0000000..c10f971
--- /dev/null
+++ b/src/Erebos/Channel.hs
@@ -0,0 +1,174 @@
+module Erebos.Channel (
+    Channel,
+    ChannelRequest, ChannelRequestData(..),
+    ChannelAccept, ChannelAcceptData(..),
+
+    createChannelRequest,
+    acceptChannelRequest,
+    acceptedChannel,
+
+    channelEncrypt,
+    channelDecrypt,
+) where
+
+import Control.Concurrent.MVar
+import Control.Monad
+import Control.Monad.Except
+
+import Crypto.Cipher.ChaChaPoly1305
+import Crypto.Error
+
+import Data.Binary
+import Data.ByteArray (ByteArray, Bytes, ScrubbedBytes, convert)
+import Data.ByteArray qualified as BA
+import Data.ByteString.Lazy qualified as BL
+import Data.List
+
+import Erebos.Identity
+import Erebos.PubKey
+import Erebos.Storage
+
+data Channel = Channel
+    { chPeers :: [Stored (Signed IdentityData)]
+    , chKey :: ScrubbedBytes
+    , chNonceFixedOur :: Bytes
+    , chNonceFixedPeer :: Bytes
+    , chCounterNextOut :: MVar Word64
+    , chCounterNextIn :: MVar Word64
+    }
+
+type ChannelRequest = Signed ChannelRequestData
+
+data ChannelRequestData = ChannelRequest
+    { crPeers :: [Stored (Signed IdentityData)]
+    , crKey :: Stored PublicKexKey
+    }
+    deriving (Show)
+
+type ChannelAccept = Signed ChannelAcceptData
+
+data ChannelAcceptData = ChannelAccept
+    { caRequest :: Stored ChannelRequest
+    , caKey :: Stored PublicKexKey
+    }
+
+
+instance Storable ChannelRequestData where
+    store' cr = storeRec $ do
+        mapM_ (storeRef "peer") $ crPeers cr
+        storeRef "key" $ crKey cr
+
+    load' = loadRec $ do
+        ChannelRequest
+            <$> loadRefs "peer"
+            <*> loadRef "key"
+
+instance Storable ChannelAcceptData where
+    store' ca = storeRec $ do
+        storeRef "req" $ caRequest ca
+        storeRef "key" $ caKey ca
+
+    load' = loadRec $ do
+        ChannelAccept
+            <$> loadRef "req"
+            <*> loadRef "key"
+
+
+keySize :: Int
+keySize = 32
+
+createChannelRequest :: (MonadStorage m, MonadIO m, MonadError String m) => UnifiedIdentity -> UnifiedIdentity -> m (Stored ChannelRequest)
+createChannelRequest self peer = do
+    (_, xpublic) <- liftIO . generateKeys =<< getStorage
+    skey <- loadKey $ idKeyMessage self
+    mstore =<< sign skey =<< mstore ChannelRequest { crPeers = sort [idData self, idData peer], crKey = xpublic }
+
+acceptChannelRequest :: (MonadStorage m, MonadIO m, MonadError String m) => UnifiedIdentity -> UnifiedIdentity -> Stored ChannelRequest -> m (Stored ChannelAccept, Channel)
+acceptChannelRequest self peer req = do
+    case sequence $ map validateIdentity $ crPeers $ fromStored $ signedData $ fromStored req of
+        Nothing -> throwError $ "invalid peers in channel request"
+        Just peers -> do
+            when (not $ any (self `sameIdentity`) peers) $
+                throwError $ "self identity missing in channel request peers"
+            when (not $ any (peer `sameIdentity`) peers) $
+                throwError $ "peer identity missing in channel request peers"
+    when (idKeyMessage peer `notElem` (map (sigKey . fromStored) $ signedSignature $ fromStored req)) $
+        throwError $ "channel requent not signed by peer"
+
+    (xsecret, xpublic) <- liftIO . generateKeys =<< getStorage
+    skey <- loadKey $ idKeyMessage self
+    acc <- mstore =<< sign skey =<< mstore ChannelAccept { caRequest = req, caKey = xpublic }
+    liftIO $ do
+        let chPeers = crPeers $ fromStored $ signedData $ fromStored req
+            chKey = BA.take keySize $ dhSecret xsecret $
+                fromStored $ crKey $ fromStored $ signedData $ fromStored req
+            chNonceFixedOur  = BA.pack [ 2, 0, 0, 0 ]
+            chNonceFixedPeer = BA.pack [ 1, 0, 0, 0 ]
+        chCounterNextOut <- newMVar 0
+        chCounterNextIn <- newMVar 0
+
+        return (acc, Channel {..})
+
+acceptedChannel :: (MonadIO m, MonadError String m) => UnifiedIdentity -> UnifiedIdentity -> Stored ChannelAccept -> m Channel
+acceptedChannel self peer acc = do
+    let req = caRequest $ fromStored $ signedData $ fromStored acc
+    case sequence $ map validateIdentity $ crPeers $ fromStored $ signedData $ fromStored req of
+        Nothing -> throwError $ "invalid peers in channel accept"
+        Just peers -> do
+            when (not $ any (self `sameIdentity`) peers) $
+                throwError $ "self identity missing in channel accept peers"
+            when (not $ any (peer `sameIdentity`) peers) $
+                throwError $ "peer identity missing in channel accept peers"
+    when (idKeyMessage peer `notElem` (map (sigKey . fromStored) $ signedSignature $ fromStored acc)) $
+        throwError $ "channel accept not signed by peer"
+    when (idKeyMessage self `notElem` (map (sigKey . fromStored) $ signedSignature $ fromStored req)) $
+        throwError $ "original channel request not signed by us"
+
+    xsecret <- loadKey $ crKey $ fromStored $ signedData $ fromStored req
+    let chPeers = crPeers $ fromStored $ signedData $ fromStored req
+        chKey = BA.take keySize $ dhSecret xsecret $
+            fromStored $ caKey $ fromStored $ signedData $ fromStored acc
+        chNonceFixedOur  = BA.pack [ 1, 0, 0, 0 ]
+        chNonceFixedPeer = BA.pack [ 2, 0, 0, 0 ]
+    chCounterNextOut <- liftIO $ newMVar 0
+    chCounterNextIn <- liftIO $ newMVar 0
+
+    return Channel {..}
+
+
+channelEncrypt :: (ByteArray ba, MonadIO m, MonadError String m) => Channel -> ba -> m (ba, Word64)
+channelEncrypt Channel {..} plain = do
+    count <- liftIO $ modifyMVar chCounterNextOut $ \c -> return (c + 1, c)
+    let cbytes = convert $ BL.toStrict $ encode count
+        nonce = nonce8 chNonceFixedOur cbytes
+    state <- case initialize chKey =<< nonce of
+        CryptoPassed state -> return state
+        CryptoFailed err -> throwError $ "failed to init chacha-poly1305 cipher: " <> show err
+
+    let (ctext, state') = encrypt plain state
+        tag = finalize state'
+    return (BA.concat [ convert $ BA.drop 7 cbytes, ctext, convert tag ], count)
+
+channelDecrypt :: (ByteArray ba, MonadIO m, MonadError String m) => Channel -> ba -> m (ba, Word64)
+channelDecrypt Channel {..} body = do
+    when (BA.length body < 17) $ do
+        throwError $ "invalid encrypted data length"
+
+    expectedCount <- liftIO $ readMVar chCounterNextIn
+    let countByte = body `BA.index` 0
+        body' = BA.dropView body 1
+        guessedCount = expectedCount - 128 + fromIntegral (countByte - fromIntegral expectedCount + 128 :: Word8)
+        nonce = nonce8 chNonceFixedPeer $ convert $ BL.toStrict $ encode guessedCount
+        blen = BA.length body' - 16
+        ctext = BA.takeView body' blen
+        tag = BA.dropView body' blen
+    state <- case initialize chKey =<< nonce of
+        CryptoPassed state -> return state
+        CryptoFailed err -> throwError $ "failed to init chacha-poly1305 cipher: " <> show err
+
+    let (plain, state') = decrypt (convert ctext) state
+    when (not $ tag `BA.constEq` finalize state') $ do
+        throwError $ "tag validation falied"
+
+    liftIO $ modifyMVar_ chCounterNextIn $ return . max (guessedCount + 1)
+    return (plain, guessedCount)