[Lightning-dev] General question on routing difficulties

Fri Nov 17 14:30:14 UTC 2017

Oh yeah, my mail tool destroyed that mail quite expertly :-)

The footnotes were
[1]
https://github.com/lightningnetwork/lightning-rfc/blob/master/07-routing-gossip.md
[2]
https://medium.com/@rusty_lightning/lightning-routing-rough-background-dbac930abbad
[3]
https://www.tik.ee.ethz.ch/file/a20a865ce40d40c8f942cf206a7cba96/Scalable_Funding_Of_Blockchain_Micropayment_Networks%20(1).pdf

We will eventually move away from the hash function based approach in favor
of something that allows us to decorrelate hops in a route. We have indeed
started writing down some of the ideas at least for Lightning in the
project's wiki [4], but they're definitely not fleshed out.

[4] https://github.com/lightningnetwork/lightning-rfc/wiki/Brainstorming

On Fri, Nov 17, 2017 at 3:10 PM Benjamin Mord <ben at mord.io> wrote:

> "I think this is exactly the right venue to discuss these kinds of
> issue..." - you are probably right! My bad.
>
> Christian, thank you for your knowledgable reply. The footnotes did not
> come through on my end, I am especially interested in [3]. Do you have a
> link? I am thrilled to hear of a Bitcoin-compatible revive alternative! :)
>
> Are we keeping an inventory somewhere of the cryptographic primitives
> being used in lightning and the specific assumptions being made about them
> (e.g. preimage resistance vs collision resistance and such)? One project I
> have not yet found but believe we need across the entire cryptocurrency
> community, is a (wiki-style?) inventory of unproven mathematical
> assumptions (e.g. hardness of discrete logarithm) and/or cryptographic
> primitives, cataloged in terms of the cryptocurrency technologies which
> require them. Such a resource could help the community respond more
> quickly, comprehensively, and transparently to the inevitable cryptanalytic
> surprises that will pop up over time (especially from the quantum
> cryptanalytic area, but even the classical cryptanalytic community as well).
>
> Related, I believe the ideal end state would be to only assume existence
> of a preimage-resistant hash function, and to code such that one function
> could be quickly swapped with another and thus update entire system. I'm
> not sure if that is a realistic goal, but here is my first attempt to move
> in that direction in case it is of interest to lightning. It is hard to
> imagine it would be a new idea, although I have not yet found the precedent:
> http://ben.mord.io/p/delayed-chained-key-revelation-dckr.html
>
> Thanks,
> Ben
>
>
> On Nov 17, 2017 8:04 AM, "Christian Decker" <decker.christian at gmail.com>
> wrote:
>
> On Thu, Nov 16, 2017 at 5:01 PM Benjamin Mord <ben at mord.io> wrote:
>
>> Ivan,
>>
>> That is mostly false, but with bits of truth sprinkled in. Contact me at
>> ben at mord.io for further discussion so we tread lightly on the lists'
>> email inboxes.
>>
>
> I think this is exactly the right venue to discuss these kinds of issue,
> so please don't move the conversation somewhere else :-)
>
> Routing is still very much in flux, we have a minimally viable routing
> protocol in the spec [1]. It is minimal in the sense that we just push
> the entire network's topology to the edges, which can then locally
> compute routes. This is effectively a source-routed network, which
> matches the requirements of the onion routing protocol we use for
> privact as well. But this does not mean that this is protocol is set in
> stone. We are actively working on finding better solutions to the
> problem of finding routes across a vast network of millions if not
> billions of nodes. Distance vector routing such as BGP uses may be one
> option like Ben suggested.
>
> For now the network can easily scale to about 1 million channels [2]
> even on very limited devices, Upgrading to another protocol at a later
> point in time is trivial, since none of the routing information is
> consensus critical. We have all the extension points built in to allow
> future extensibility.
>
>
>> But briefly: scale-capable routing protocols are possible as demonstrated
>> by IP and thus by the internet itself. As for centralizing flow through
>> small number of liquidity providers, yes that does seem economically
>> probable, at least unless / until off-chain channel rebalancing mechanism
>> (like the recently proposed "revive" protocol) come about. Bitcoin script
>> is not currently revive-capable but Ethereum is, so either Bitcoin revive
>> could be enabled via two-way pegged sidechain protocol with Ethereum, or
>> even better, by a purpose-built (yet still not Turing-complete) extension
>> to Bitcoin script itself in the future.
>>
>
> As a matter of fact, Conrad and I just published a similar technique for
> off-chain channel rebalancing and fund re-allocation based solely on
> Bitcoin [3] (major props to Conrad for the excellent writeup!). The
> flexibility in Bitcoin exists.
>
> As for the hubs everybody is assuming will form, I don't think they're
> as likely to form. Creating such a hub is extremely costly since it'll
> have to allocate sufficient funds to cover the maximum imbalance of all
> of its channels ahead of time. Then the fees must cover the opportunity
> cost of allocating all of those funds to channels instead of investing
> them somewhere else. On top of that the funds will not be moved alot
> since they serve only a small number of endpoints connected through
> those channels, this compounds the problem of having high fees. The high
> fees make the hub channels a really bad choice for your payments, after
> all you were looking for small fees for your payments, right? It opens
> up an opportunity for nodes to open bypasses that grab some of the
> traffic and associated fees from the expensive hub.
>
> All of that being said, we should be careful about our predictions on
> how the topology will look, I added some counter arguments to a
> hub-and-spoke network forming, but nobody can really be sure about
> what'll happen.
>
>
>> In either case the lightning network seems a key first step, and even
>> were off-chain payment rebalancing not possible for some odd reason, the
>> lightning network seems extremely valuable and scaleable - regardless
>> because the centralization you speak is not one that affects safety of the
>> money supply itself, and these centralized hubs would be more dispensable /
>> swappable versus the mining centralization risk that people more often talk
>> about in Bitcoin. Lightning network centralization, even if it persisted
>> somehow despite revive and future concepts, would not be an existential
>> risk.
>>
>
> Rebalancing is definitely possible, even without [3], you can
> disincentivize the use of a channel until they have been rebalanced. For
> long term imbalance, opening another channel may be the best option
>
>
>> As for transaction fees, the idea is only channel setup / tear down are
>> required greatly reducing fees. Yes if txin fees were millions of dollars
>> then people could not practically penalize fraud, but that is unlikely.
>> Even if txin fees made fraud claims marginally unprofitable (yet practical)
>> that would still be ok - the judicial systems of most countries prove that
>> people go beyond self-interest when sufficiently ticked, a fact of human
>> psychology which in turn creates the incentives that support honest
>> business. (Also please be aware I'm not a lightning code contributor, so
>> that team might also be doing more to address already than I thought to
>> mention above.)
>>
>
> This is open to speculation as well. We hope to reduce the load on the
> on-chain network sufficiently to allow timely on-chain settlements. By
> aggregating payments off-chain we can also aggregate the fees and then
> use them to pay on-chain fees. So don't consider the on-chain fees for
> your channels as your sole loss, they are paid for by payments you
> forward. Ultimately this should encourage participants to open channels
> that support the network as a whole, not just themselves. We are
> building automations that should take care of this, the user won't have
> to do anything to improve the network topology.
>
> Cheers,
> Christian
>
>
>
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