A compute-hard real-time in-browser solution that doesn’t rely on exotic encryption appears infeasible. (You’d need a GPU, and hours/days worth of compute for years of locking).
For LW, perhaps threshold aggregate time-lock encryption would suffice (though vulnerable to collusion/bribery attacks, as noted by Gwern).
I agree with Quintin Pope, a public hash is simple and effective.
Gwern has a fantastic overview of time-lock encryption methods.
A compute-hard real-time in-browser solution that doesn’t rely on exotic encryption appears infeasible. (You’d need a GPU, and hours/days worth of compute for years of locking). For LW, perhaps threshold aggregate time-lock encryption would suffice (though vulnerable to collusion/bribery attacks, as noted by Gwern).
I agree with Quintin Pope, a public hash is simple and effective.