[Lightning-dev] Fat Errors

Rusty Russell rusty at rustcorp.com.au
Mon Oct 24 22:32:52 UTC 2022


Joost Jager <joost.jager at gmail.com> writes:
> Hi list,
>
> I wanted to get back to a long-standing issue in Lightning: gaps in error
> attribution. I've posted about this before back in 2019 [1].

Hi Joost!

        Thanks for writing this up fully.  Core lightning also doesn't
penalize properly, because of the attribution problem: solving this lets
us penalize a channel, at least.

        I want to implement this too, to make sure I understand it
correctly, but having read it twice it seems reasonable.

        How about 16 hops?  It's the closest power of 2 to the legacy hop
limit, and makes this 4.5k for payloads and hmacs.

        There is, however, a completely different possibility if we want
to use a pre-pay scheme, which I think I've described previously.  You
send N sats and a secp point; every chained secret returned earns the
forwarder 1 sat[1].  The answers of course are placed in each layer of
the onion.  You know how far the onion got based on how much money you
got back on failure[2], though the error message may be corrupted.

Cheers,
Rusty.
[1] Simplest is truncate the point to a new secret key.  Each node would
    apply a tweak for decorrelation ofc.
[2] The best scheme is that you don't get paid unless the next node
    decrypts, actually, but that needs more thought.


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