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, 0 insertions, 6 deletions

diff --git a/TODO b/TODO
index 0d98317..5a070da 100644
--- a/TODO
+++ b/TODO
@@ -21,12 +21,6 @@
   multiple developers, as each time a developer gets an Activity Seen,
   they can update their state to use the Activity Entered that it points
   to.
-* 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.
-  (If doing this, might as well switch to SHA512, since hash size does not
-  matter.)
 * loadLog should verify the hashes (and signatures) in the log, and
   refuse to use logs that are not valid proofs of a session.
   (--replay and --graphvis need this; server's use of loadLog does not)