Leave the prevMessage out of Activity serialization to save BW.

Do include it in the data that gets signed, so it can be recovered
by trying each likely (recently seen) Activity as the prevMessage, and
checking the signature.

The UserState and DeveloperState already had the necessary state about
recently seen hashes, so this does not impact data use.

One tricky bit is that relayFromSocket needs to wait for the TMChan
to be empty before calling restorePrevActivityHash. Otherwise, the
hashes of items in the channel that have not been processed yet won't be
tried. The TMChan is not really being used as a channel since only 1
item can be in it. It could be converted to a TMVar, but closeTMChan is
used so I left it as a channel.

Note that the server does not restore hashes of messages that pass
through it; it's just a dumb relay.

Sending a single key press now only needs 94 bytes of data to be sent,
down from 169!

---

Also switched to SHA512, since hashes are no longer being sent over
the wire and so the larger size does not matter. SHA512 is slightly
faster and more secure.

This commit was sponsored by Ewen McNeill.

1 files changed, 4 insertions, 26 deletions

diff --git a/ProtocolBuffers.hs b/ProtocolBuffers.hs
index 6d02096..53dfca0 100644
--- a/ProtocolBuffers.hs
+++ b/ProtocolBuffers.hs
@@ -40,7 +40,9 @@ data MessageP a
 
 data ActivityP a = ActivityP
 	{ activityP :: Required 6 (Message a)
-	, prevAtivityP :: Optional 7 (Message HashP)
+	-- This is not included, because the hash is never actually sent
+	-- over the wire!
+	-- , prevAtivityP :: Optional 7 (Message HashP)
 	, elapsedTimeP :: Required 8 (Message ElapsedTimeP)
 	, activitySignatureP :: Required 9 (Message SignatureP)
 	}
@@ -63,12 +65,6 @@ data ControlActionP
 		{ sessionKeyRejectedP :: Required 15 (Message PublicKeyP) }
 	deriving (Generic)
 
-data HashP = HashP
-	{ hashMethodP :: Required 16 (Value B.ByteString)
-	, hashValueP :: Required 17 (Value B.ByteString)
-	}
-	deriving (Generic)
-
 data SignatureP
 	= Ed25519SignatureP
 		{ ed25519SignatureP :: Required 18 (Value B.ByteString) }
@@ -141,13 +137,12 @@ instance ProtocolBuffer (ActivityP p) (T.Activity t) => ProtocolBuffer (MessageP
 instance ProtocolBuffer p t => ProtocolBuffer (ActivityP p) (T.Activity t) where
 	toProtocolBuffer t = ActivityP
 		{ activityP = putField $ toProtocolBuffer $ T.activity t
-		, prevAtivityP = putField $ fmap toProtocolBuffer $ T.prevActivity t
 		, elapsedTimeP = putField $ toProtocolBuffer $ T.elapsedTime t
 		, activitySignatureP = putField $ toProtocolBuffer $ T.activitySignature t
 		}
 	fromProtocolBuffer p = T.Activity
 		{ T.activity = fromProtocolBuffer $ getField $ activityP p
-		, T.prevActivity = fmap fromProtocolBuffer $ getField $ prevAtivityP p
+		, T.prevActivity = Nothing -- not sent over the wire
 		, T.elapsedTime = fromProtocolBuffer $ getField $ elapsedTimeP p
 		, T.activitySignature = fromProtocolBuffer $ getField $ activitySignatureP p
 		}
@@ -180,21 +175,6 @@ instance ProtocolBuffer ControlActionP T.ControlAction where
 	fromProtocolBuffer p@(SessionKeyRejectedP {}) = T.SessionKeyRejected $
 		fromProtocolBuffer $ getField $ sessionKeyRejectedP p
 
-instance ProtocolBuffer HashP T.Hash where
-	toProtocolBuffer t = HashP
-		{ hashMethodP = putField $ case T.hashMethod t of
-			T.SHA256 -> "2"
-			T.SHA3 -> "3"
-		, hashValueP = putField $ val $ T.hashValue t
-		}
-	fromProtocolBuffer p = T.Hash
-		{ T.hashMethod = case getField (hashMethodP p) of
-			"2" -> T.SHA256
-			"3" -> T.SHA3
-			_ -> T.SHA256
-		, T.hashValue = Val $ getField $ hashValueP p
-		}
-
 instance ProtocolBuffer SignatureP T.Signature where
 	toProtocolBuffer (T.Ed25519Signature t) = Ed25519SignatureP
 		{ ed25519SignatureP = putField $ val t }
@@ -252,8 +232,6 @@ instance Encode ControlP
 instance Decode ControlP
 instance Encode ControlActionP
 instance Decode ControlActionP
-instance Encode HashP
-instance Decode HashP
 instance Encode SignatureP
 instance Decode SignatureP
 instance Encode PublicKeyP