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module PrevActivity where
import Types
import Crypto
import Control.Concurrent.STM
-- | Remove the prevActivity from a message. Doing this before sending
-- it over the wire saves transmitting that data, without weakening
-- security at all.
removePrevActivityHash :: AnyMessage -> AnyMessage
removePrevActivityHash msg = case msg of
User (ActivityMessage a) -> User (go a)
Developer (ActivityMessage a) -> Developer (go a)
_ -> msg
where
go a = ActivityMessage $ a { prevActivity = Nothing }
type RecentActivity = STM (SigVerifier, [Hash])
noRecentActivity :: RecentActivity
noRecentActivity = return (mempty, [])
-- | Restore the prevActivity to a message received without one.
-- This needs a RecentActivity cache, and it tries hashes from that cache
-- as the prevActivity until it finds one that makes the message's
-- signature verify.
restorePrevActivityHash :: RecentActivity -> AnyMessage -> STM AnyMessage
restorePrevActivityHash ra msg = case msg of
User (ActivityMessage act) ->
User . ActivityMessage <$> (go act =<< ra)
Developer (ActivityMessage act) ->
Developer . ActivityMessage <$> (go act =<< ra)
User (ControlMessage {}) -> return msg
Developer (ControlMessage {}) -> return msg
where
go act (_, []) = return act
go act (sigverifier, (h:hs)) = do
let act' = act { prevActivity = Just h }
if verifySigned sigverifier act'
then return act'
else go act (sigverifier, hs)
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