From aj at erisian.com.au  Mon Oct 11 06:29:51 2021
From: aj at erisian.com.au (Anthony Towns)
Date: Mon, 11 Oct 2021 16:29:51 +1000
Subject: [Lightning-dev] Lightning over taproot with PTLCs
In-Reply-To: <20211009011207.GA3984@erisian.com.au>
References: <20211009011207.GA3984@erisian.com.au>
Message-ID: <20211011062951.GA5165@erisian.com.au>

On Sat, Oct 09, 2021 at 11:12:07AM +1000, Anthony Towns wrote:
>  2. The balance transaction - tracks the funding transaction, contains
>     a "balance" output for each of the participants.
>  3. The inflight transactions - spends a balance output from the balance
>     transaction and provides outputs for any inflight htlc/ptlc transactions.
>  4. Layered transactions - spends inflight htlc/ptlc outputs by revealing
>     the preimage, while still allowing for the penalty path.

I don't think the layering here quite works: if Alice forwarded a payment
to Bob, with timeout T, then the only way she can be sure that she can
either reclaim the funds or know the preimage by time T is to close the
channel on-chain at time T-to_self_delay.

Any time later than that, say T-to_self_delay+x+1, would allow Bob to
post the inflight tx at T+x (prior to Alice being able to claim her
balance directly due to the to_self_delay) and then immediately post the
layered transaction (4, above) revealing the preimage, and preventing
Alice from claiming the refund.

Cheers,
aj