Olaoluwa Osuntokun [ARCHIVE] on Nostr: 📅 Original date posted:2017-11-25 📝 Original message: (re-sending as doesn't ...
📅 Original date posted:2017-11-25
📝 Original message:
(re-sending as doesn't look like my original mail went through to the list?)
Hi Pedro,
I came across this paper a few weeks ago, skimmed it lightly, and noted a
few interesting aspects I wanted to dig into later. Your email reminded me
to re-read the paper, so thanks for that! Before reading the paper, I
wasn't aware of the concept of coordinate embedding, nor how that could be
leveraged in order to provide sender+receiver privacy in a payment network
using a distance-vector-like routing system. Very cool technique!
After reading the paper again, my current conclusion is that while the
protocol presents some novel traits in the design a routing system for
payment channel based networks, it lends much better to a
closed-membership, credit network, such as Ripple (which is the focus of
the paper).
In Ripple, there are only a handful of gateways, and clients that seek to
interact with the network must chose their gateways *very* carefully,
otherwise consensus faults can occur, violating safety properties of the
network. It would appear that this gateway model nicely translates well to
the concept of landmarks that the protocol is strongly dependant on.
Ideally, each gateway would be a landmark, and as there are a very small
number of gateways within Ripple (as you must be admitted to be a verified
gateway in the network), then parameter L (the total number of landmarks)
is kept small which minimizes routing overhead, the average path-length,
etc.
When we compare Ripple to LN, we find that the two networks are nearly
polar opposites of each other. LN is an open-membership network that
requires zero initial configuration by central administrators(s). It more
closely resembles *debit* network (a series of tubes of money), as the
funds within channels must be pre-committed in order to establish a link
between two nodes, and cannot be increased without an additional on-chain
control transaction (to add or remove funds). Additionally, AFAIK (I'm no
expert on Ripple of course), there's no concept of fees within the
network. While within LN, the fee structure is a critical component of the
inventive for node operators to lift their coins onto this new layer to
provider payment routing services. Finally, in LN we rely on time-locks
in order to ensure that all transactions are atomic which adds another set
of constraints. Ripple has no such constraint as transfers are based on
bi-lateral trust.
With that said, the primary difference between this protocol is that
currently we utilize a source-routed system which requires the sender to
know "most" of the path to the destination. I say "most" as currently,
it's possible for the receiver of a payment to use a poor man's rendezvous
system to provide the sender with a set of suffix paths form what one can
consider ad-hoc landmarks. The sender can then concatenate these with
their own paths, and construct the Sphinx routing package which encodes
the full route. This itself only gives sender privacy, and the receiver
doesn't know the identity of the sender, but the sender learns the
identity of the receiver.
We have plans to achieve proper sender/receiver privacy by extending our
Sphinx usage to leverage HORNET, such that the payment descriptor (payment
request containing details of the payment) also includes several paths
from rendezvous nodes (Rodrigo's) to the receiver. The rendezvous route
itself will be nested as a further Anonymous Header (AHDR) which includes
the information necessary to complete the onion circuit from Rodrigo to
the receiver. As onion routing is used, only Rodrigo can decrypt the
payload and finalize the route. With such a structure, the only nodes that
need to advertise their channels are nodes which seek to actively serve as
channel routers. All other nodes (phones, laptops, etc), don't need to
advertise their channels to the greater network, reducing the size of the
visible network, and also the storage and validation overhead. This serves
to extend the "scale ceiling" a bit.
My first question is: is it possible to adapt the protocol to allow each
intermediate node to communicate their time lock and fee references to the
sender? Currently, as the full path isn't known ahead of time, the sender
is unable to properly craft the timelocks to ensure safety+atomicity of
the payment. This would mean they don't know what the total timelock
should be on the first outgoing link. Additionally, as they don't know the
total path and the fee schedule of each intermediate node, then once
again, they don't know how much to send on the first out going link. It
would seem that one could extend the probing phase to allow backwards
communication by each intermediate node back to the sender, such that they
can properly craft a valid HTLC. This would increase the set up costs of
the protocol however, and may also increase routing failures as it's
possible incompatibilities arise at run-time between the preferences of
intermediate nodes. Additionally, routes may fail as an intermediate node
consumes too many funds as their fee, causing the funds to be insufficient
when it reaches the destination. One countermeasure would maybe: the
sender always sends waaay more than necessary, and gives the receiver a
one-time payment identifier, requiring that they route the remainder of
the funds *back* to them.
To solve this issue presently, we extend the header in Sphinx to include a
per-hop payload which allows the sender to precisely dictate the
structure of the route, allows the intermediate nodes to authenticate the
information given to it, and also allow the intermediate node to verify
that their policies have properly been respected. These payloads can also
be utilized by applications to communicate a small-ish amount of data to
construct higher-level protocols on top of the system. Examples include:
cross-chain swaps, chance payment games, higher-level B2B protocols,
flavors of ZKCP's, media streaming, internet access proxying, etc.
>From my point-of-view, when extended to LN, the core component of the
protocol (landmarks), becomes the weakest component. From my reading,
*all* nodes need to be ware of an *identical* set of landmarks (more or
less similar to the desired homogeneity of Gateways), otherwise the
coordinate embedding scheme breaks down. Currently, there's no requirement
that all nodes have a globally consistent view of the network. So then an
important questions arises: who choose the landmarks? A desirable property
of a routing system for LN (IMO) is that is has close to zero required
initial set up by a central administrator. With this protocol, it would
seem that all nodes much ship with a hard coded set of global landmarks
for the path finding to succeed. This itself pins a hard coordination
requirement amongst implementers to have something like this deployed.
Even ignoring this requirement for a minute, I see several other
downsides:
* As *all* payments must flow through landmarks (since nodes break up
their payment into L sub-flows), the landmarks must be very, very
well capitalized. This would cause strong consolidation of the
selection of landmarks, as they need extremely large channels in
order to facilitate transfer within the network.
* As landmarks must be globally known, this it seems this would
introduce fragility in the network. If most of the landmarks go down
(fails stop crashes) due to hardware issues, DoS, exploited bugs,
etc, then the network's throughput instantly becomes crippled.
* If all payment flow *must* go through landmarks, and the transfers
within the network are relatively uni-directional (all payment going
to Candy Crush Ultra: Lighting Strikes Twice), then their
channels would become unbalanced very quickly.
The last point there invokes another component of the network: passive
channel rebalancing. With source routing, it's possible for nodes to
passive rebalance their channels, in order to keep the in equilibrium,
such that on average they'll be able to handle a payment flow coming from
any direction. This is possible as with source routing, it's easy for a
node to simply send a payment to himself incoming/outgoing from the pair
of channels they wish to adjust the available flow of. With
distance-vector-like protocols, this doesn't seem possible, as the node
doesn't have any control of the incoming channel that the payment will
arrive on.
Finally, the notion of value privacy within the scheme seems a bit weak.
>From this definition, any protocol that didn't broadcast intents to send
payments to the world would achieve this trait. The base Bitcoin
blockchain doesn't mask the values of transfers (yet), but even if it did
unconditionally maintaining value privacy of channel doesn't seem
compatible with multi-hop payment networks (nodes can simply perform
probing/tagging attacks to ascertain a range of the size of a channel). A
possible mitigation would be for nodes to probabilistically drop incoming
payments, with all nodes sampling from the same distribution. However,
this would dramatically increase routing failures by senders, removing the
"low-latency" trait of payment networks that many find desirable.
Personally, I've very excited to see additional research on the front of
routing within the network! Excellent work by all authors.
In the end, I don't think it'll be a one-size fits all solution, as each
routing protocol delivers with it a set of tradeoffs that should be
weighed depending on target characteristics, and use-cases. There's no
strong requirement that the network as a whole uses a *single* routing
protocol. Instead several distinct protocols can be deployed based on
use-case requirements, as we only need to share a single end-to-end
construct: the HTLC. I could see a future in a few years where we have
several deployed protocols, similar to the wide array of existing routing
protocols deployed on the Internet. What we have currently gets us from
Zero to One. We'll definitely need to experiment with additional
approaches as the size of the network grows, and the true economic flow
patterns emerge after we all deploy to mainnet.
-- Laolu
On Tue, Nov 21, 2017 at 9:38 AM Pedro Moreno Sanchez <pmorenos at purdue.edu>
wrote:
> Hello,
>
> my name is Pedro Moreno-Sanchez and I am a PhD student at the computer
> science department at Purdue. I would like to bring to your attention a
> novel routing algorithm suitable for the Lightning Network (LN) that I
> have been working on with my supervisor Prof. Aniket Kate (Purdue
> University) and my co-workers Stefanie Roos and Prof. Ian Goldberg
> (University of Waterloo).
>
> Our approach is called SpeedyMurmurs, a routing algorithm for
> decentralized payment networks such as the LN. SpeedyMurmurs uses an
> embedding-based approach, meaning that the algorithm assigns meaningful
> coordinates to nodes that enable efficient and effective discovery of
> payment paths. In a nutshell, SpeedyMurmurs creates a spanning tree by
> means of a Breadth-First Search and then associates a coordinate to each
> node depending on its position in the tree. A path from the sender to
> the receiver is then calculated in a flexible manner, with each
> intermediate node choosing the next node in the path as a function of
> its neighbors' coordinates, available funds and closeness to the
> receiver. To account for topology changes (e.g., a new channel is
> created), the routing information is locally updated by only those
> affected nodes in the network.
>
> We have simulated several configurations of SpeedyMurmurs using real
> data from the Ripple network and compared it with other routing
> algorithms available in the literature. Our simulation results show that
> SpeedyMurmurs is able to find paths at about twice faster, reduces the
> communication overhead by at least a factor of 2 and maintains a similar
> or higher payment success ratio. Our simulation framework is open source
> and we believe that it might be of independent interest for this
> community to test this and any other alternative protocols that you
> might have in mind. If you are interested, we are happy to extend on this.
>
> Finally, we also show that SpeedyMurmurs achieves the privacy notions of
> interest in the LN. In particular, SpeedyMurmurs achieves value privacy,
> i.e., the total value of a transaction remains hidden, as well as sender
> and receiver privacy, i.e., the identities of the two transacting nodes
> remain hidden from the adversary.
>
>
> You can find all the details in the draft of our paper [1]. The final
> version of this work will appear at NDSS 2018 conference [2]. We would
> be glad to hear any question and feedback from you and are open to carry
> out further collaborations if this line of work is of interest for you.
>
> Best regards,
> Pedro, Stef, Aniket and Ian.
>
> [1] https://arxiv.org/abs/1709.05748
> [2] https://www.ndss-symposium.org/
>
> On 11/17/17 8:09 PM, Saravanan Vijayakumaran wrote:
> > Hi Christian,
> >
> > Are there any open source simulators available for trying different
> > routing strategies? Or even a simulator for the Lightning network as a
> > whole?
> >
> > Regards
> > sarva
> >
> >
> > On Fri, Nov 17, 2017 at 8:00 PM, Christian Decker
> > <decker.christian at gmail.com <mailto:decker.christian at gmail.com>> wrote:
> >
> > 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
> > <
> https://secure-web.cisco.com/1wkWGu7k6qIvsw8KxbTL8XXIpbTYjcgzOohVSUjpLJpNW0_r00YaFlguhX0pSCEAg2qU5kztXF4bxEpLbMz-RLAz9KTBvE0lh3kFGUjL5qke6yx8EcYvhHQQSttWjRX5HOt69vu8suXd7AhjEweVxeBFhvptINqjBarDx7woqCa14ZgWZdMk0dAt45Lnu_w1wjgn3j5sD7tBo187MGXR94eapimiMFjXySj70GeP1yiEA8rP0NUQ5CSXme2wQy-spVW_SLQpvkAQ01NlXUjK-ufQw_APez6C73Qx0bFh_9F-CPhKhhvM3tSs6IGNEM63aXMVeti2Ci0R5Xc15tvcT9gxpC32bNetja5ber6wbIHLbI9FWviQ63cWaNwhedQRN/https%3A%2F%2Fgithub.com%2Flightningnetwork%2Flightning-rfc%2Fblob%2Fmaster%2F07-routing-gossip.md
> >
> > [2]
> >
> https://medium.com/@rusty_lightning/lightning-routing-rough-background-dbac930abbad
> > <
> https://secure-web.cisco.com/1UG1OaEI1KFpQ4prjxrhN1Wsxs0P1Tco0MXQz0xltJZQjwI-sNi98eXMz-gW4qOQd2jJ4i0uktvL8CH-9RrmEg3GkxHfcxjnjxY_hlLP-ctXOYMSk4BFbySy7vD5xWivimHIfMHtr13ffgEoFLItUgoajxUe7tnkchPN_P5OZ_FOzYdpqW_UDdgWW0_VOsccR5yt1vh0MRyVxO2B2ua8k4NmbFgTmht6hxUlXDsXOsOSGDHm1WO5VNrRbUcGeTPpdBMx0xeyZ9FTMTBCIAMOZ6UEb_eAX3X1iVIFkP_MPtuJcp0q8t9Tk_UBs-dHVRjyYcCsnetXYNI_mEsdtyg63aLXuJE1pMLb8-eamWaFfklVo-w9N9F0XTbmbkgGfcWU4/https%3A%2F%2Fmedium.com%2F%40rusty_lightning%2Flightning-routing-rough-background-dbac930abbad
> >
> > [3]
> >
> https://www.tik.ee.ethz.ch/file/a20a865ce40d40c8f942cf206a7cba96/Scalable_Funding_Of_Blockchain_Micropayment_Networks%20(1).pdf
> > <
> https://secure-web.cisco.com/1XOlJdRo0gtzmPhNfVlEpMsrVBAI6BSjdDawPogEDIwYDdva2BSx4H8F9B3E6bkVIqA7ByFEF85qVjJ775leFwE54p5G6-wHH4Cio0p9sYLJ14-NHwcwvYQ--zdI8hdAyjGQbcLltVFAmorMaTlHq4FGI1CmxlwiUYgH1tjZn3UAHOu5xm5pLVi6KTb9WsJvuJsOBJhLfRLWGcAhVbjRXuV8b3x_G4ybOg1CQYC9ZVq3RJCPnNgQ3BN3a5ZuzW4veOE_dgi80FEy1x7a8spH-TV-cb_fey6ud-S25AWQ1PbctVS5zgQ4Ki4XYkR5igotNGGbWhACevBJfU1Hxqk90_g-DgQtS9_e_UX_FsY-yAjw/https%3A%2F%2Fwww.tik.ee.ethz.ch%2Ffile%2Fa20a865ce40d40c8f942cf206a7cba96%2FScalable_Funding_Of_Blockchain_Micropayment_Networks%2520%281%29.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
> > <
> https://secure-web.cisco.com/1XqVZXht8sW8tdbLxwEMjoU-hxxV6OJwpKqc2OudZy26Le21yvOIBPwqizepwLi9TBeEV2BMDc-nCiKpj3eryi59jqvoZcBRrSQSVt9Qrq8pIxNSvhIMlG4cRd3lnj17JT9mDRRt0lS51C_9gpryV6qFqdiROdyJeTKfqUGmnvPo3isfeUbC_TOOfWLDV16jYA38ytCfTOryyDvJgJdYw7ArAUEMg10jNv8lV9aTARBOcOmgLjqJt0ktecsUpUCfIVAQlJEvtAAbWAUKwMoXg6MpIQEA4NE1ATntmwjLGl4IqQEqRAGxkGxWI8yQDL74yPPTIQmGTxs_JXE6YYMrhuD93GR1kyUJkOAH3Z_5nL1bsr3ifW31PJtUckQNnwY8e/https%3A%2F%2Fgithub.com%2Flightningnetwork%2Flightning-rfc%2Fwiki%2FBrainstorming
> >
> >
> >
> > On Fri, Nov 17, 2017 at 3:10 PM Benjamin Mord <ben at mord.io
> > <mailto: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
> > <
> http://secure-web.cisco.com/1ewGQFfIxw1QZwneD3sDbhSSWP-YTmBwOYe529E7_zeYZZADnASbspvBAftPFXX6ZxJI2l2-8-xEqdpkmFg3fEIfkfRBYN8oZ8Z0HpeHh73MnT3Zi3M8GUs8SGMww38ZPnzsc7xlt7H5KFlLMcCsTWIgEtq4roZHDkYasanNeViP_UA3DIod7A281fNvWnQ1mnLs6d8WN_uFx1diU_xr-EoMab3wyANozirDj1gZ2_yPBn6S8tePYMkTkhIZlLz_BlvIfk9_KCOOiUcWxDTtCq9KdvoqEzStC04Z6q8xS5rtSnmK9GZZxv30yrgT8eWA4eOzce6AA3m0WEClNzbzANgi11GXBVde9pNiUIRcLDNw/http%3A%2F%2Fben.mord.io%2Fp%2Fdelayed-chained-key-revelation-dckr.html
> >
> >
> > Thanks,
> > Ben
> >
> >
> > On Nov 17, 2017 8:04 AM, "Christian Decker"
> > <decker.christian at gmail.com <mailto:decker.christian at gmail.com>>
> > wrote:
> >
> > On Thu, Nov 16, 2017 at 5:01 PM Benjamin Mord <ben at mord.io
> > <mailto:ben at mord.io>> wrote:
> >
> > Ivan,
> >
> > That is mostly false, but with bits of truth sprinkled
> > in. Contact me at ben at mord.io <mailto: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
> >
> >
> >
> > _______________________________________________
> > Lightning-dev mailing list
> > Lightning-dev at lists.linuxfoundation.org
> > <mailto:Lightning-dev at lists.linuxfoundation.org>
> > https://lists.linuxfoundation.org/mailman/listinfo/lightning-dev
> > <
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📝 Original message:
(re-sending as doesn't look like my original mail went through to the list?)
Hi Pedro,
I came across this paper a few weeks ago, skimmed it lightly, and noted a
few interesting aspects I wanted to dig into later. Your email reminded me
to re-read the paper, so thanks for that! Before reading the paper, I
wasn't aware of the concept of coordinate embedding, nor how that could be
leveraged in order to provide sender+receiver privacy in a payment network
using a distance-vector-like routing system. Very cool technique!
After reading the paper again, my current conclusion is that while the
protocol presents some novel traits in the design a routing system for
payment channel based networks, it lends much better to a
closed-membership, credit network, such as Ripple (which is the focus of
the paper).
In Ripple, there are only a handful of gateways, and clients that seek to
interact with the network must chose their gateways *very* carefully,
otherwise consensus faults can occur, violating safety properties of the
network. It would appear that this gateway model nicely translates well to
the concept of landmarks that the protocol is strongly dependant on.
Ideally, each gateway would be a landmark, and as there are a very small
number of gateways within Ripple (as you must be admitted to be a verified
gateway in the network), then parameter L (the total number of landmarks)
is kept small which minimizes routing overhead, the average path-length,
etc.
When we compare Ripple to LN, we find that the two networks are nearly
polar opposites of each other. LN is an open-membership network that
requires zero initial configuration by central administrators(s). It more
closely resembles *debit* network (a series of tubes of money), as the
funds within channels must be pre-committed in order to establish a link
between two nodes, and cannot be increased without an additional on-chain
control transaction (to add or remove funds). Additionally, AFAIK (I'm no
expert on Ripple of course), there's no concept of fees within the
network. While within LN, the fee structure is a critical component of the
inventive for node operators to lift their coins onto this new layer to
provider payment routing services. Finally, in LN we rely on time-locks
in order to ensure that all transactions are atomic which adds another set
of constraints. Ripple has no such constraint as transfers are based on
bi-lateral trust.
With that said, the primary difference between this protocol is that
currently we utilize a source-routed system which requires the sender to
know "most" of the path to the destination. I say "most" as currently,
it's possible for the receiver of a payment to use a poor man's rendezvous
system to provide the sender with a set of suffix paths form what one can
consider ad-hoc landmarks. The sender can then concatenate these with
their own paths, and construct the Sphinx routing package which encodes
the full route. This itself only gives sender privacy, and the receiver
doesn't know the identity of the sender, but the sender learns the
identity of the receiver.
We have plans to achieve proper sender/receiver privacy by extending our
Sphinx usage to leverage HORNET, such that the payment descriptor (payment
request containing details of the payment) also includes several paths
from rendezvous nodes (Rodrigo's) to the receiver. The rendezvous route
itself will be nested as a further Anonymous Header (AHDR) which includes
the information necessary to complete the onion circuit from Rodrigo to
the receiver. As onion routing is used, only Rodrigo can decrypt the
payload and finalize the route. With such a structure, the only nodes that
need to advertise their channels are nodes which seek to actively serve as
channel routers. All other nodes (phones, laptops, etc), don't need to
advertise their channels to the greater network, reducing the size of the
visible network, and also the storage and validation overhead. This serves
to extend the "scale ceiling" a bit.
My first question is: is it possible to adapt the protocol to allow each
intermediate node to communicate their time lock and fee references to the
sender? Currently, as the full path isn't known ahead of time, the sender
is unable to properly craft the timelocks to ensure safety+atomicity of
the payment. This would mean they don't know what the total timelock
should be on the first outgoing link. Additionally, as they don't know the
total path and the fee schedule of each intermediate node, then once
again, they don't know how much to send on the first out going link. It
would seem that one could extend the probing phase to allow backwards
communication by each intermediate node back to the sender, such that they
can properly craft a valid HTLC. This would increase the set up costs of
the protocol however, and may also increase routing failures as it's
possible incompatibilities arise at run-time between the preferences of
intermediate nodes. Additionally, routes may fail as an intermediate node
consumes too many funds as their fee, causing the funds to be insufficient
when it reaches the destination. One countermeasure would maybe: the
sender always sends waaay more than necessary, and gives the receiver a
one-time payment identifier, requiring that they route the remainder of
the funds *back* to them.
To solve this issue presently, we extend the header in Sphinx to include a
per-hop payload which allows the sender to precisely dictate the
structure of the route, allows the intermediate nodes to authenticate the
information given to it, and also allow the intermediate node to verify
that their policies have properly been respected. These payloads can also
be utilized by applications to communicate a small-ish amount of data to
construct higher-level protocols on top of the system. Examples include:
cross-chain swaps, chance payment games, higher-level B2B protocols,
flavors of ZKCP's, media streaming, internet access proxying, etc.
>From my point-of-view, when extended to LN, the core component of the
protocol (landmarks), becomes the weakest component. From my reading,
*all* nodes need to be ware of an *identical* set of landmarks (more or
less similar to the desired homogeneity of Gateways), otherwise the
coordinate embedding scheme breaks down. Currently, there's no requirement
that all nodes have a globally consistent view of the network. So then an
important questions arises: who choose the landmarks? A desirable property
of a routing system for LN (IMO) is that is has close to zero required
initial set up by a central administrator. With this protocol, it would
seem that all nodes much ship with a hard coded set of global landmarks
for the path finding to succeed. This itself pins a hard coordination
requirement amongst implementers to have something like this deployed.
Even ignoring this requirement for a minute, I see several other
downsides:
* As *all* payments must flow through landmarks (since nodes break up
their payment into L sub-flows), the landmarks must be very, very
well capitalized. This would cause strong consolidation of the
selection of landmarks, as they need extremely large channels in
order to facilitate transfer within the network.
* As landmarks must be globally known, this it seems this would
introduce fragility in the network. If most of the landmarks go down
(fails stop crashes) due to hardware issues, DoS, exploited bugs,
etc, then the network's throughput instantly becomes crippled.
* If all payment flow *must* go through landmarks, and the transfers
within the network are relatively uni-directional (all payment going
to Candy Crush Ultra: Lighting Strikes Twice), then their
channels would become unbalanced very quickly.
The last point there invokes another component of the network: passive
channel rebalancing. With source routing, it's possible for nodes to
passive rebalance their channels, in order to keep the in equilibrium,
such that on average they'll be able to handle a payment flow coming from
any direction. This is possible as with source routing, it's easy for a
node to simply send a payment to himself incoming/outgoing from the pair
of channels they wish to adjust the available flow of. With
distance-vector-like protocols, this doesn't seem possible, as the node
doesn't have any control of the incoming channel that the payment will
arrive on.
Finally, the notion of value privacy within the scheme seems a bit weak.
>From this definition, any protocol that didn't broadcast intents to send
payments to the world would achieve this trait. The base Bitcoin
blockchain doesn't mask the values of transfers (yet), but even if it did
unconditionally maintaining value privacy of channel doesn't seem
compatible with multi-hop payment networks (nodes can simply perform
probing/tagging attacks to ascertain a range of the size of a channel). A
possible mitigation would be for nodes to probabilistically drop incoming
payments, with all nodes sampling from the same distribution. However,
this would dramatically increase routing failures by senders, removing the
"low-latency" trait of payment networks that many find desirable.
Personally, I've very excited to see additional research on the front of
routing within the network! Excellent work by all authors.
In the end, I don't think it'll be a one-size fits all solution, as each
routing protocol delivers with it a set of tradeoffs that should be
weighed depending on target characteristics, and use-cases. There's no
strong requirement that the network as a whole uses a *single* routing
protocol. Instead several distinct protocols can be deployed based on
use-case requirements, as we only need to share a single end-to-end
construct: the HTLC. I could see a future in a few years where we have
several deployed protocols, similar to the wide array of existing routing
protocols deployed on the Internet. What we have currently gets us from
Zero to One. We'll definitely need to experiment with additional
approaches as the size of the network grows, and the true economic flow
patterns emerge after we all deploy to mainnet.
-- Laolu
On Tue, Nov 21, 2017 at 9:38 AM Pedro Moreno Sanchez <pmorenos at purdue.edu>
wrote:
> Hello,
>
> my name is Pedro Moreno-Sanchez and I am a PhD student at the computer
> science department at Purdue. I would like to bring to your attention a
> novel routing algorithm suitable for the Lightning Network (LN) that I
> have been working on with my supervisor Prof. Aniket Kate (Purdue
> University) and my co-workers Stefanie Roos and Prof. Ian Goldberg
> (University of Waterloo).
>
> Our approach is called SpeedyMurmurs, a routing algorithm for
> decentralized payment networks such as the LN. SpeedyMurmurs uses an
> embedding-based approach, meaning that the algorithm assigns meaningful
> coordinates to nodes that enable efficient and effective discovery of
> payment paths. In a nutshell, SpeedyMurmurs creates a spanning tree by
> means of a Breadth-First Search and then associates a coordinate to each
> node depending on its position in the tree. A path from the sender to
> the receiver is then calculated in a flexible manner, with each
> intermediate node choosing the next node in the path as a function of
> its neighbors' coordinates, available funds and closeness to the
> receiver. To account for topology changes (e.g., a new channel is
> created), the routing information is locally updated by only those
> affected nodes in the network.
>
> We have simulated several configurations of SpeedyMurmurs using real
> data from the Ripple network and compared it with other routing
> algorithms available in the literature. Our simulation results show that
> SpeedyMurmurs is able to find paths at about twice faster, reduces the
> communication overhead by at least a factor of 2 and maintains a similar
> or higher payment success ratio. Our simulation framework is open source
> and we believe that it might be of independent interest for this
> community to test this and any other alternative protocols that you
> might have in mind. If you are interested, we are happy to extend on this.
>
> Finally, we also show that SpeedyMurmurs achieves the privacy notions of
> interest in the LN. In particular, SpeedyMurmurs achieves value privacy,
> i.e., the total value of a transaction remains hidden, as well as sender
> and receiver privacy, i.e., the identities of the two transacting nodes
> remain hidden from the adversary.
>
>
> You can find all the details in the draft of our paper [1]. The final
> version of this work will appear at NDSS 2018 conference [2]. We would
> be glad to hear any question and feedback from you and are open to carry
> out further collaborations if this line of work is of interest for you.
>
> Best regards,
> Pedro, Stef, Aniket and Ian.
>
> [1] https://arxiv.org/abs/1709.05748
> [2] https://www.ndss-symposium.org/
>
> On 11/17/17 8:09 PM, Saravanan Vijayakumaran wrote:
> > Hi Christian,
> >
> > Are there any open source simulators available for trying different
> > routing strategies? Or even a simulator for the Lightning network as a
> > whole?
> >
> > Regards
> > sarva
> >
> >
> > On Fri, Nov 17, 2017 at 8:00 PM, Christian Decker
> > <decker.christian at gmail.com <mailto:decker.christian at gmail.com>> wrote:
> >
> > 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
> > <
> https://secure-web.cisco.com/1wkWGu7k6qIvsw8KxbTL8XXIpbTYjcgzOohVSUjpLJpNW0_r00YaFlguhX0pSCEAg2qU5kztXF4bxEpLbMz-RLAz9KTBvE0lh3kFGUjL5qke6yx8EcYvhHQQSttWjRX5HOt69vu8suXd7AhjEweVxeBFhvptINqjBarDx7woqCa14ZgWZdMk0dAt45Lnu_w1wjgn3j5sD7tBo187MGXR94eapimiMFjXySj70GeP1yiEA8rP0NUQ5CSXme2wQy-spVW_SLQpvkAQ01NlXUjK-ufQw_APez6C73Qx0bFh_9F-CPhKhhvM3tSs6IGNEM63aXMVeti2Ci0R5Xc15tvcT9gxpC32bNetja5ber6wbIHLbI9FWviQ63cWaNwhedQRN/https%3A%2F%2Fgithub.com%2Flightningnetwork%2Flightning-rfc%2Fblob%2Fmaster%2F07-routing-gossip.md
> >
> > [2]
> >
> https://medium.com/@rusty_lightning/lightning-routing-rough-background-dbac930abbad
> > <
> https://secure-web.cisco.com/1UG1OaEI1KFpQ4prjxrhN1Wsxs0P1Tco0MXQz0xltJZQjwI-sNi98eXMz-gW4qOQd2jJ4i0uktvL8CH-9RrmEg3GkxHfcxjnjxY_hlLP-ctXOYMSk4BFbySy7vD5xWivimHIfMHtr13ffgEoFLItUgoajxUe7tnkchPN_P5OZ_FOzYdpqW_UDdgWW0_VOsccR5yt1vh0MRyVxO2B2ua8k4NmbFgTmht6hxUlXDsXOsOSGDHm1WO5VNrRbUcGeTPpdBMx0xeyZ9FTMTBCIAMOZ6UEb_eAX3X1iVIFkP_MPtuJcp0q8t9Tk_UBs-dHVRjyYcCsnetXYNI_mEsdtyg63aLXuJE1pMLb8-eamWaFfklVo-w9N9F0XTbmbkgGfcWU4/https%3A%2F%2Fmedium.com%2F%40rusty_lightning%2Flightning-routing-rough-background-dbac930abbad
> >
> > [3]
> >
> https://www.tik.ee.ethz.ch/file/a20a865ce40d40c8f942cf206a7cba96/Scalable_Funding_Of_Blockchain_Micropayment_Networks%20(1).pdf
> > <
> https://secure-web.cisco.com/1XOlJdRo0gtzmPhNfVlEpMsrVBAI6BSjdDawPogEDIwYDdva2BSx4H8F9B3E6bkVIqA7ByFEF85qVjJ775leFwE54p5G6-wHH4Cio0p9sYLJ14-NHwcwvYQ--zdI8hdAyjGQbcLltVFAmorMaTlHq4FGI1CmxlwiUYgH1tjZn3UAHOu5xm5pLVi6KTb9WsJvuJsOBJhLfRLWGcAhVbjRXuV8b3x_G4ybOg1CQYC9ZVq3RJCPnNgQ3BN3a5ZuzW4veOE_dgi80FEy1x7a8spH-TV-cb_fey6ud-S25AWQ1PbctVS5zgQ4Ki4XYkR5igotNGGbWhACevBJfU1Hxqk90_g-DgQtS9_e_UX_FsY-yAjw/https%3A%2F%2Fwww.tik.ee.ethz.ch%2Ffile%2Fa20a865ce40d40c8f942cf206a7cba96%2FScalable_Funding_Of_Blockchain_Micropayment_Networks%2520%281%29.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
> > <
> https://secure-web.cisco.com/1XqVZXht8sW8tdbLxwEMjoU-hxxV6OJwpKqc2OudZy26Le21yvOIBPwqizepwLi9TBeEV2BMDc-nCiKpj3eryi59jqvoZcBRrSQSVt9Qrq8pIxNSvhIMlG4cRd3lnj17JT9mDRRt0lS51C_9gpryV6qFqdiROdyJeTKfqUGmnvPo3isfeUbC_TOOfWLDV16jYA38ytCfTOryyDvJgJdYw7ArAUEMg10jNv8lV9aTARBOcOmgLjqJt0ktecsUpUCfIVAQlJEvtAAbWAUKwMoXg6MpIQEA4NE1ATntmwjLGl4IqQEqRAGxkGxWI8yQDL74yPPTIQmGTxs_JXE6YYMrhuD93GR1kyUJkOAH3Z_5nL1bsr3ifW31PJtUckQNnwY8e/https%3A%2F%2Fgithub.com%2Flightningnetwork%2Flightning-rfc%2Fwiki%2FBrainstorming
> >
> >
> >
> > On Fri, Nov 17, 2017 at 3:10 PM Benjamin Mord <ben at mord.io
> > <mailto: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
> > <
> http://secure-web.cisco.com/1ewGQFfIxw1QZwneD3sDbhSSWP-YTmBwOYe529E7_zeYZZADnASbspvBAftPFXX6ZxJI2l2-8-xEqdpkmFg3fEIfkfRBYN8oZ8Z0HpeHh73MnT3Zi3M8GUs8SGMww38ZPnzsc7xlt7H5KFlLMcCsTWIgEtq4roZHDkYasanNeViP_UA3DIod7A281fNvWnQ1mnLs6d8WN_uFx1diU_xr-EoMab3wyANozirDj1gZ2_yPBn6S8tePYMkTkhIZlLz_BlvIfk9_KCOOiUcWxDTtCq9KdvoqEzStC04Z6q8xS5rtSnmK9GZZxv30yrgT8eWA4eOzce6AA3m0WEClNzbzANgi11GXBVde9pNiUIRcLDNw/http%3A%2F%2Fben.mord.io%2Fp%2Fdelayed-chained-key-revelation-dckr.html
> >
> >
> > Thanks,
> > Ben
> >
> >
> > On Nov 17, 2017 8:04 AM, "Christian Decker"
> > <decker.christian at gmail.com <mailto:decker.christian at gmail.com>>
> > wrote:
> >
> > On Thu, Nov 16, 2017 at 5:01 PM Benjamin Mord <ben at mord.io
> > <mailto:ben at mord.io>> wrote:
> >
> > Ivan,
> >
> > That is mostly false, but with bits of truth sprinkled
> > in. Contact me at ben at mord.io <mailto: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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> > Lightning-dev at lists.linuxfoundation.org
> > <mailto:Lightning-dev at lists.linuxfoundation.org>
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