diff --git a/src/Game.hs b/src/Game.hs
index eff01fd..bb48118 100644
--- a/src/Game.hs
+++ b/src/Game.hs
@@ -21,7 +21,10 @@ import Hanafuda.KoiKoi (Game, Mode(..), Player, PlayerID, Players)
 import qualified Hanafuda.KoiKoi as KoiKoi (
     Action, Game(..), Move(..), play, new
   )
-import Hanafuda.Message (PrivateState(..), PublicGame(..), PublicPlayer(..), PublicState(..))
+import Hanafuda.Message (
+      GameState(..), PrivateState(..), PublicGame(..), PublicPlayer(..)
+    , PublicState(..)
+  )
 import qualified Hanafuda.Player as Player (Player(..), Players(..), get)
 import Keys (T(..))
 import qualified Keys (public, secret)
@@ -35,9 +38,16 @@ exportPlayers game =
   let (Player.Players players) = KoiKoi.players game in
   players
 
-privateState :: Game -> PrivateState
-privateState game = PrivateState {
-      hands = Player.hand <$> players
+getGameState :: Game -> GameState
+getGameState game = GameState {
+      gameID = KoiKoi.gameID game
+    , turns = 24 - length (KoiKoi.deck game)
+  }
+
+privateState :: GameState -> Game -> PrivateState
+privateState link game = PrivateState {
+      link
+    , hands = Player.hand <$> players
     , deck = KoiKoi.deck game
   }
   where
@@ -59,9 +69,10 @@ privatePlayer publicPlayers playerID hand = Player.Player {
     , Player.yakus = yakus (publicPlayers ! playerID)
   }
 
-publicState :: Game -> PublicState
-publicState game = PublicState {
-      mode = KoiKoi.mode game
+publicState :: GameState -> Game -> PublicState
+publicState gameState game = PublicState {
+      gameState
+    , mode = KoiKoi.mode game
     , scores = KoiKoi.scores game
     , month = KoiKoi.month game
     , nextPlayer = KoiKoi.nextPlayer game
@@ -72,7 +83,6 @@ publicState game = PublicState {
     , river = KoiKoi.river game
     , step = KoiKoi.step game
     , trick = KoiKoi.trick game
-    , turns = 24 - length (KoiKoi.deck game)
     , rounds = KoiKoi.rounds game
   }
 
@@ -88,15 +98,17 @@ exportGame playerID game = do
       , publicSignature = signDetached (Keys.secret sign) $ toJSON public
     }
   where
-    public = publicState game
-    private = privateState game
+    sharedState = getGameState game
+    public = publicState sharedState game
+    private = privateState sharedState game
 
 toJSON :: ToJSON a => a -> ByteString
 toJSON = toStrict . encode
 
-gameOf :: PublicState -> PrivateState -> Game
-gameOf public private = KoiKoi.Game {
-        KoiKoi.mode = mode public
+merge :: PublicState -> PrivateState -> Game
+merge public private = KoiKoi.Game {
+        KoiKoi.gameID = gameID $ gameState public
+      , KoiKoi.mode = mode public
       , KoiKoi.scores = scores public
       , KoiKoi.month = month public
       , KoiKoi.nextPlayer = nextPlayer public
@@ -113,18 +125,22 @@ gameOf public private = KoiKoi.Game {
     }
 
 importGame :: PublicGame -> App.T (Either String Game)
-importGame PublicGame {nonce, private, public, publicSignature} = do
-  Keys.T {encrypt, sign} <- App.get Server.keys
-  if signVerifyDetached (Keys.public sign) publicSignature $ toJSON public
-  then return $ do
+importGame PublicGame {nonce, private, public, publicSignature} =
+  App.get Server.keys >>= \(Keys.T {encrypt, sign}) -> return $ do
+    check (signVerifyDetached (Keys.public sign) publicSignature (toJSON public))
+      `orDie` "The game state has been tampered with"
     n <- Saltine.decode nonce `orDie` "Could not decode nonce"
     decrypted <- secretboxOpen encrypt n private
                   `orDie` "Could not decrypt private state"
-    gameOf public <$> eitherDecode' (fromStrict decrypted)
-  else return $ Left "The game state has been tampered with"
+    decoded <- eitherDecode' (fromStrict decrypted)
+    check (link decoded == gameState public)
+      `orDie` "Private and public parts do not match"
+    return $ merge public decoded
   where
     orDie :: Maybe a -> String -> Either String a
     orDie m errorMessage = maybe (Left errorMessage) Right m
+    check :: Bool -> Maybe ()
+    check test = if test then Just () else Nothing
 
 play :: PlayerID -> KoiKoi.Move -> PublicGame -> App.T (Either String (Game, [KoiKoi.Action]))
 play playerID move publicGame