This week’s newsletter briefly describes a proposal for splicing Lightning Network payment channels, links to videos and transcripts of talks from the Edge Dev++ training sessions, and summarizes some transcripts made during last week’s event.

Action items

None this week.


  • Proposal for Lightning Network payment channel splicing: splicing is an idea for allowing users to either add or remove funds from an existing payment channel without the delay of closing and reopening a completely new channel. Rusty Russell posted a technical proposal for allowing a single splice at a time, although he notes that the proposal is complex. René Pickhardt described an alternative that would likely be easier to implement and reason about but which could require more onchain transactions. It was suggested that the simpler but more expensive solution could be version 1, and the more complex but less expensive solution could be version 2.

  • Edge Dev++ talks published: a two-day series of presentations from leading Bitcoin contributors aimed at developers has been published as videos and transcripts. The talks cover the full range of topics, from introductory to advanced. Three talks may be especially interesting to Optech members:

    1. Exchange security by Warren Togami. Describes the causes behind several notable major thefts from Bitcoin and altcoin exchanges and lists a number of techniques businesses can use to reduce their risk of loss. (Video, transcript)

    2. Wallet Security, Key Management & Hardware Security Modules (HSMs)] by Bryan Bishop. Suggests methods for decreasing the risk that private keys will be stolen or misused. (Video, transcript)

    3. Handling reorgs and forks by Bryan Bishop. Describes how to secure your transactions against changes in the Bitcoin block chain or consensus rules, including suggestions for how to test your systems. (Video, transcript) is an invite-only event for well-known contributors to Bitcoin infrastructure projects such as Bitcoin Core and Lightning Network. Discussions are not recorded, but Bryan Bishop helpfully writes rough and non-authoritative transcripts of some of the discussions during the events. The following short summaries are based on some of the transcripts for the event in Tokyo last week:

  • Bitcoin Optech: Bitcoin Optech is introduced and briefly discussed, followed by discussion of common problems Bitcoin-using businesses encounter when using Bitcoin Core and other open source infrastructure projects.

  • Using UTXO accumulators to reduce data storage requirements: Tadge Dryja describes work he’s been doing on UTXO accumulators that are similar in function to those described in last week’s newsletter but which have a different construction based on hashes. He further describes how they could be combined with something like Cory Field’s UTXO Hash Set (UHO) idea for full nodes to store hashes of UTXOs instead of full UTXOs in order to significantly reduce the amount of storage pruned full nodes would use without necessarily requiring any changes to the consensus rules.

  • Script descriptors and DESCRIPT: the backwards-compatible way wallets such as Bitcoin Core default to watching for transaction outputs paying them “is ambiguous, inflexible, and scales badly”. Output script descriptors are a simple language for describing scripts to the wallet that makes it easier for the wallet to handle many normal cases (including imports of HD extended private and public keys).

    Somewhat related is DESCRIPT, a language that uses a subset of the full Bitcoin Script language to make it easy to construct some simple policies. “We have a DESCRIPT compiler that takes something we’re calling a policy language (AND, OR, threshold, public key, hashlock, timelock) together with probabilities for each OR to tell whether it’s 50/50 or whether one side of the OR is more likely than the right, and it will find […] the optimal script in this subset of script that we have defined.” For example, it could allow you “to do something like a multisig that after some time degrades into a weaker multisig—like a 2-of-3 but after a year I can spend it with just one of those keys.”

Notable code changes

Notable code changes this week in Bitcoin Core, LND, and C-lightning.

  • LND #1970: The AbandonChannel RPC method (only available in the developer debug mode) now provides additional information when users tell their node to abandon a payment channel (a method that can cause monetary loss if used carelessly). The additional information is enough to allow either restarting an open payment channel later or to prove that the program had enough information to make additional commitments to a now-closed payment channel.

  • C-Lightning #2000: This provides a large number of fixes and safety-related improvements how hash-timelocked-contracts (HTLCs) are stored in the database.