Hi Antoine
I've got a lot to catch up on re channel jamming but just to say I'm deeply
skeptical about attempting to embed a reputation layer or reputation
credentials into the Lightning protocol. Admittedly I'm somewhat of a curious
amateur in the field of reputation systems but a number of people (me included)
have had to look into reputation systems in the past for projects/startups they
were working on and centralized​​ reputation systems are absolute minefields to
manage effectively though some corporations do manage it. Decentralized
reputation systems baked into a protocol is just a step too far. All you need
is one edge case where the attacker can ensure an innocent party is blamed and
the reputation system falls apart. The protocol developer is in the position of
assessing who is telling the truth out of two opposing viewpoints on Reddit etc.
I do think reputation systems will play a key part in a future Lightning
Network (to some extent they already are with sites like 1ML and Amboss) but
they won't be managed by protocol devs, they will be managed by multiple
flavors of companies and projects (hopefully open source but most likely closed
source too, for profit, non-profit etc) who are free to use whatever metrics
and weigh those metrics however they like. The protocol just can't afford to
expand into areas where there is case by case judgment and statistical analysis
required. It will become bloated, ineffective and put protocol developers in
the position of deciding who ultimately receives routing fees rather than just
enabling payments can get from A to B. Identity is easier, you either control a
private key or you don't. Reputation is much more difficult, there will be some
attacks where a probabilistic assessment will need to be made on who the
perpetrator of the attack was. You don't add that to the (already long) list of
protocol developers' responsibilities.
So feel free to continue to explore reputation and reputation systems but a
strong warning that this is likely not solved at the protocol level. Decisions
protocol developers make will impact what data can be collected and how easy
that data is to collect (there are already some tricky trade-offs with regards
to privacy, routing success and transparency for when things go wrong) but
beyond that protocol developers should leave it to others. I've included some
links to some additional reading on reputation systems in case you are
interested.
Thanks
Michael
[0]:
https://www.amazon.com/Building-Reputation-Systems-Randy-Farmer/dp/059615979X/
[1]:
https://medium.com/openbazaarproject/decentralized-reputation-in-openbazaar-1a577fac5175
[2]: https://www.bitrated.com/faq
--
Michael Folkson
Email: michaelfolkson at [protonmail.com](http://protonmail.com/)
Keybase: michaelfolkson
PGP: 43ED C999 9F85 1D40 EAF4 9835 92D6 0159 214C FEE3
------- Original Message -------
On Monday, November 21st, 2022 at 06:01, Antoine Riard
<antoine.ri...@gmail.com> wrote:
> Hi LN Devs,
>
> tl;dr A formalization of a reputation-based scheme to solve channel jamming
> is proposed. The system relies on "credentials" issued by routing hops and
> requested to be attached to each HTLC forward request. The "credentials" can
> be used by a reputation algorithm to reward/punish payment senders and
> allocate channel liquidity resources efficiently. The "credentials" initial
> distribution can be bootstrapped leveraging one-time upfront fees paid toward
> the routing hops. Afterwards, the "credentials" subsequent distribution can
> rely on previous HTLC traffic.
>
> A protocol description can be found here, with few extensions already to the
> BOLTs:
>
> https://github.com/lightning/bolts/pull/1043
>
> There is also a work-in-progress proof-of-concept in LDK (on top of our
> coming soon^TM HTLC intercepting API):
>
> https://github.com/lightningdevkit/rust-lightning/pull/1848
>
> This work builds on previous reputation-scheme research [0] [1]. It also
> integrates the more recent proposals of upfront fees as a straightforward
> mechanism to bootstrap the reputation system. Bootstrapping the system with
> more economically cost-effective privacy-preserving UTXO ownership proofs not
> only add another layer of engineering complexity, there is still a proof size
> vs proof generation/validation trade-off to arbiter between ZKP cryptosystems.
>
> Rather to seek for a game-theory equilibrium defined as a breakeven point as
> in the latest unconditional fee research [2], this proposal aims to use
> reputation credentials to allow HTLC traffic-shaping. This not only should
> protect against jamming situations (either malicious
> or spontaneous) but also allow active HTLC traffic-shaping, where a routing
> hop can allow extended channel liquidity lockups based on accumulated
> reputation (e.g for hold-invoices). This is also a reduced overhead cost, as
> upfront fees are only paid at bootstrap, or when the HTLC forward behavior
> can be qualified as "whitewashing" from the routing hop viewpoint.
>
> It should be noted, this current reputation-credential architectural
> framework assumes credentials distribution at the endpoint of the network.
> However, the framework should be flexible enough for the credentials to be
> harvested by the LSPs, and then distributed in a secondary fashion to their
> spokes, when they need it, or even attached transparently thanks to
> trampoline. So one design intuition, there is no strong attachment of the
> reputation to the endpoint HTLC sender, even if the protocol is described in
> a "flat" view for now.
>
> Let's evaluate quickly this mitigation proposal against a few criterias
> emerged from recent research.
>
> The mitigation is effective, in the sense a routing hop can apply a
> proportional relationship between the acquisition of the reputation and the
> amount of liquidity resources credited in function of said reputation. In a
> period of steady state, the reputation acquisition cost can be downgraded to
> 0. In periods of channel congestion, the reputation credentials to liquidity
> units translation can be severed, in the limit of routing hop acceptable
> competitiveness.
>
> The mitigation is incentive-compatible, if the credentials are not honored by
> their issuers, the HTLC senders can evict them from the routing network view
> for a while. The successful usage of credentials can lead to more credentials
> allocated for longer and more capacity-intensive channel lockups. In case of
> HTLC failure, the failure source could be forgiven by routing hops to
> maintain the worthiness of the sender credentials.
>
> The mitigation can be made transparent from the user, as the credentials
> harvesting can be done automatically from a pre-allocated budget, similar to
> the fee-bumping reserves requirement introduced by anchor output. At the end
> of today, if we take modern browsers as an example, the average user doesn't
> check manually the TLS certificates (for what they're worth...).
>
> The mitigation can conserve high-level privacy, as the usage of blinded
> signature (or another equivalent cryptosystem breaking signature/message
> linking) should allow the credentials issued during a preliminary phase to be
> undistinguishable during the redeem/usage phase. New CPU/memory DoS vectors
> due to the credentials processing should be watched out.
>
> About the ease of implementation, there are few protocol messages to modify,
> a HTLC intercepting API is assumed as supported by the implementation, onion
> messages support is also implied, landing EC blinded signature in
> libsecp256k1-zkp shouldn't be a big deal, routing algorithms adaptations
> might be more serious but still reasonable. The "credentials-to-liquidity"
> allocation algorithms are likely the new real beast, though I don't think any
> reputation scheme can spare them.
>
> There could be a concern about the centralization inertia introduced by a
> reputation system. Intuitively, the argument can be made that any historical
> tracking (such as routing buckets) favor established LN incumbents at the
> gain of efficiency. A counter-argument can be made, a new routing hop can
> lower the acquisition cost of its issued credentials to attract more HTLC
> traffic (accepting higher jamming risk).
>
> On the ecosystem impacts, it should be studied that this proposal would
> impact things like inbound channel routing fees [3], ratecard [4] or
> flow-control valve [5] and the whole liquidity toolchain. Hopefully, we don't
> significantly restrain the design space for future LN protocol upgrades.
>
> On the proposal modularity and flexibility, each routing node has oversight
> on its routing policy, acquisition methods, credentials to liquidity rate.
> New acquisition methods can be experimented or deployed when ready, e.g
> stakes certificates with only e2e upgrade. The credentials themselves could
> have "innate" expiration time if we use things like short-lived ZKP [6]. The
> credentials framework can be extended beyond solving jamming, as a
> generalized risk-management framework for Bitcoin decentralized financial
> network, e.g transaction signature exchange ordering in multi-party
> transactions [7] or finding reliable Coinjoin counterparties.
>
> Feedback welcome.
>
> Cheers,
> Antoine
>
> [0]
> https://lists.linuxfoundation.org/pipermail/lightning-dev/2020-November/002884.html
> [1]
> https://lists.linuxfoundation.org/pipermail/lightning-dev/2022-August/003673.html
> [2]
> https://lists.linuxfoundation.org/pipermail/lightning-dev/2022-November/003740.html
> [3]
> https://lists.linuxfoundation.org/pipermail/lightning-dev/2022-July/003643.html
> [4]
> https://lists.linuxfoundation.org/pipermail/lightning-dev/2022-September/003685.html
> [5]
> https://lists.linuxfoundation.org/pipermail/lightning-dev/2022-September/003686.html
> [6] https://eprint.iacr.org/2022/190.pdf
> [7] https://github.com/lightning/bolts/pull/851#issuecomment-1290727242
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