Hi all,
Nicolas Dorier was requesting additional hooks in c-lightning for a simple
WatchTower system: https://github.com/ElementsProject/lightning/issues/1353
Unfortunately I was only able to provide an interface which requires a
*trusted* WatchTower. Trust is of course a five-letter word and should not be
used in polite company.
My key problem is that I provide enough information to the WatchTower for the
WatchTower to be able to create the justice transaction by itself. If so, the
WatchTower could just make the justice transaction output to itself and the
counterparty, so that the WatchTower and the counterparty can cooperate to
steal the channel funds: the counterparty publishes a revoked transaction, the
WatchTower writes a justice transaction on it that splits the earnings between
itself and the counterparty.
It seems to me, that the only safe way to implement a trustless WatchTower, is
for the node to generate a fully-signed justice transaction, IMMEDIATELY after
every commitment transaction is revoked, and transmit it to the WatchTower.
The WatchTower would have to store each and every justice transaction it
received, and would not be able to compress it or use various techniques to
store data efficiently. The WatchTower would not have enough information to
regenerate justice transactions (and in particular would not be able to create
a travesty-of-justice transaction that pays out to itself rather than the
protected party). In practice this would require that node software also keep
around those transactions until some process has ensured that the WatchTower
has received the justice transactions.
Is there a good way to make trustless WatchTowers currently or did this simply
not reach BOLT v1.0?
Regards,
ZmnSCPxj
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