[Lightning-dev] Probing final receiver with refund timeout

Mats Jerratsch mats at blockchain.com
Mon Mar 21 09:42:35 UTC 2016


> OK, let me get the proposal straight:
> 
> 1.  Each node will publish its MIN_TIMEOUT (along
>    with its other info as per Option 2 in
>    http://lists.linuxfoundation.org/pipermail/lightning-dev/2015-October/000262.html )
> 
> 2.  The payer sums the MIN_TIMEOUT to the payee, adds some random value
>    (keeping it under the max value allowed by protocol) to give the
>    initial HTLC timeout.
> 
> 3.  The payer puts the 'expected_timeout' in each layer of the onion, by
>    subtracting the last hops' MIN_TIMEOUT from the initial timeout.
> 
> eg.  Say maximum allowed timeout is 20 * 12 hours, and route is:
> 
>        A (12 hours) -> B (6 hours) -> C (6 hours) -> D (4 hours)
> 
>     Initial timeout has to be at least 12 + 6 + 6 + 4 == 28 hours, plus
>     some padding for transmission delays, say 29 hours.

I take a multiply of the MIN_TIMEOUT, a factor around 2, but yes, that sounds about right

> 
>     It picks a random timeout between 29 and 240 hours, say now+100 hours,
>     and onion looks like:
> 
>     [ A: now+100 [ B: now+88 [ C: now+82 [ D: now+76 ] ] ] ]

I would not use the MIN_TIMEOUT here, but use it as the minimum time I deduct each hop and add some randomness into it.
It also means that you need two values in the onion object:

(1) the value you expect to receive
(2) the value you should use for the next hop (and therefore the (1) value of the next hop))

So somewhere along this:
    [ A: now+100;now+80 [ B: now+80;now+65 [ C: now+65;now+54 [ D: now+54;now+40 ] ] ] ]
which can obviously be saved in a less redundant way

Cheers
Mats

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