[Lightning-dev] Force close of channel with unresolved htlc

[René Pickhardt]

Dear Subhra,

as discussed bilaterally and after clarification of your question the
situation is as follows:

Let us assume A and B have a channel in which A has 4 tokens and B has 6
tokens

Now A offers an HTLC with the amount of 2 tokens and B accepts (receives)
the offer then A and B both have negotiated the HTLC output in the most
recent commitment transaction.

If A stops responding and B has to force close the channel a commitment
transaction with 3 UTXOs will hit the chain. One UTXO with 2 tokens
spendable by A, another one with 6 tokens spendable by B and the received
HTLC output with 2 tokens. This one can be spend by two different
conditions as in the offchain protocol

1.) Before the timelock of the HTLC has passed B can spend the output if B
knows his to_local HTLC secret AND the preimage. OR
2.) after the timelock A can spend the output if A knows the to_remote HTLC
secret.

the mechanism with HTLCs can be read upon in BOLT 2 (channel operation
https://github.com/lightningnetwork/lightning-rfc/blob/master/02-peer-protocol.md)
and the scripts can be seen in BOLT 3:
https://github.com/lightningnetwork/lightning-rfc/blob/master/03-transactions.md

A less technical summary that is more focused on explaining the concepts is
currently being developed in the routing chapter of mastering the lightning
network:
https://github.com/lnbook/lnbook/blob/43ce57298b4da345286ae3b53c42ea3eb9d9b056/routing.asciidoc

With kind regards Rene Pickhardt

On Tue, May 5, 2020 at 8:06 PM Subhra Mazumdar <
subhra.mazumdar1993 at gmail.com> wrote:

> Hi,
>      I am having a doubt regarding force closure of channel. Suppose A->B
> there is an htlc which has been established for transfering fund. Now
> suppose for some unfortunate reason B doesnt have the witness to resolve
> htlc and the mean time A suffers crash fault. Then can B close the channel
> given that it has no way out of resolving the htlc due to lack of witness?
> _______________________________________________
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> Lightning-dev at lists.linuxfoundation.org
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https://www.rene-pickhardt.de

Skype: rene.pickhardt

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