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Bitcoin Optech Newsletter #228
This week’s newsletter describes a proposal to mitigate LN jamming attacks using reputation credential tokens. Also included are our regular sections with announcements of new software releases and release candidates and summaries of notable changes to popular Bitcoin infrastructure software.
● Reputation credentials proposal to mitigate LN jamming attacks: Antoine Riard posted to the Lightning-Dev mailing list a proposal for a new credential-based reputation system to help prevent attackers from temporarily blocking payment (HTLC) slots or value, preventing honest users from being able to send payments—a problem called channel jamming attacks.
In LN today, spenders choose a path from their node to the receiving node across multiple channels operated by independent forwarding nodes. They create a set of trustless instructions that describes where each forwarding node should next relay the payment, encrypting those instructions so that each node receives only the minimum information it needs to do its job.
Riard proposes that each forwarding node should only accept the relay instructions if they include one or more credential tokens that were previously issued by that forwarding node. The credentials include a blind signature that prevents the forwarding node from directly determining which node was issued the credential (preventing the forwarding node from learning the network identity of the spender). Each node may issue credentials according to its own policy, although Riard suggests several distribution methods:
● Upfront payments: if Alice’s node wants to forward payments through Bob’s node, her node first uses LN to buy a credential from Bob.
● Previous success: if a payment that Alice sent through Bob’s node is successfully accepted by the ultimate receiver, Bob’s node can return a credential token to Alice’s node—or even more tokens than were previously used, allowing Alice’s node to send additional value through Bob’s node in the future.
● UTXO ownership proofs or other alternatives: although not necessary for Riard’s initial proposal, some forwarding nodes may experiment with giving credentials to everyone who proves they own a Bitcoin UTXO, perhaps with modifiers that give older or higher-value UTXOs more credential tokens than newer or lower-value UTXOs. Any other criteria can be used as each forwarding node chooses for itself how to distribute its credential tokens.
Clara Shikhelman, whose own co-authored proposal partly based on local reputation was described in Newsletter #226, replied to ask whether credential tokens were transferable between users and whether that could lead to the creation of a market for tokens. She also asked how they would work with blinded paths where a spending node wouldn’t know the full path to the receiving node.
Riard replied that it would be difficult to redistribute credential tokens and create a market for them because any transfer would require trust. For example, if Bob’s node issues a new credential to Alice, who then tries to sell the credential to Carol, there’s no trustless way for Alice to prove she won’t try to use the token herself even after Carol has paid her.
For blinded paths, it appears the receiver can provide any necessary credentials in an encrypted form without introducing a secondary vulnerability.
Additional feedback for the proposals was received on its related pull request.
Releases and release candidates
New releases and release candidates for popular Bitcoin infrastructure projects. Please consider upgrading to new releases or helping to test release candidates.
● LND 0.15.5-beta.rc2 is a release candidate for a maintenance release of LND. It contains only minor bug fixes according to its planned release notes.
● Core Lightning 22.11rc3 is a release candidate for the next major version of CLN. It’ll also be the first release to use a new version numbering scheme, although CLN releases continue to use semantic versioning.
Notable code and documentation changes
Notable changes this week in Bitcoin Core, Core Lightning, Eclair, LDK, LND, libsecp256k1, Hardware Wallet Interface (HWI), Rust Bitcoin, BTCPay Server, BDK, Bitcoin Improvement Proposals (BIPs), and Lightning BOLTs.
● Core Lightning #5727 begins deprecating numeric JSON request IDs in favor of IDs using the string type. Documentation is added describing the benefit of string IDs and how to get the most out of creating and interpreting them.
● Eclair #2499 allows specifying a blinded route to use when using a BOLT12 offer to request payment. The route may include a route leading up to the user’s node plus additional hops going past it. The hops going past the node won’t be used, but they will make it harder for the spender to determine how many hops the receiver is from the last non-blinded forwarding node in the route.
● LND #7122 adds support to
lnclifor processing binary PSBT files. BIP174 specifies that PSBTs may be encoded either as plain text Base64 or binary in a file. Prior, LND already supported importing Base64-encoded PSBTs either as plain text or from file.
● LDK #1852 accepts a feerate increase proposed by a channel peer even if that feerate isn’t high enough to safely keep the channel open at present. Even if the new feerate isn’t entirely safe, its higher value means it’s safer than what the node had before, so it’s better to accept it than try to close the channel with its existing lower feerate. A future change to LDK may close channels with feerates that are too low, and work on proposals like package relay may make anchor outputs or similar techniques adaptable enough to eliminate concerns about present feerates.
● Libsecp256k1 #993 includes in the default build options the modules for extrakeys (functions for working with x-only pubkeys), ECDH, and schnorr signatures. The module for reconstructing a public key from a signature is still not built by default “because we don’t recommend ECDSA recovery for new protocols. In particular, the recovery API is prone to misuse: It invites the caller to forget to check the public key (and the verification function always returns 1).”