This edition of the Bitcoin Optech Newsletter covers a proposal for splicing Lightning Network payment channels, highlights talks from the Edge Dev++ training sessions, and summarizes key discussions from the recent CoreDev.tech event. We also provide updates on notable code changes in major Bitcoin and Lightning Network implementations.
What's New in Bitcoin and Lightning Development
Lightning Network Payment Channel Splicing Proposal
Splicing is a technique that allows users to add or remove funds from an existing payment channel without the delay of closing and reopening a completely new channel. Rusty Russell recently published a technical proposal enabling single splicing operations, though he noted the approach is complex. In response, René Pickhardt described a simpler alternative that may be easier to implement and reason about, albeit potentially requiring more on-chain transactions. Some developers have suggested that a simpler, higher-cost solution could serve as version 1, with a more complex, cost-efficient version following as version 2.
Edge Dev++ Training Sessions Now Available
A two-day series of talks from leading Bitcoin contributors, aimed at developers, has been released in both video and transcript formats. The sessions cover topics ranging from beginner to advanced levels. Three talks are particularly relevant for Optech members:
- Exchange Security by Warren Togami: This presentation examines the causes behind several major Bitcoin and altcoin exchange thefts and outlines techniques businesses can use to mitigate risk. (Video, Transcript)
- Wallet Security, Key Management, and Hardware Security Modules (HSMs) by Bryan Bishop: This talk offers practical advice for reducing the risk of private key theft or misuse. (Video, Transcript)
- Handling Reorganizations and Forks by Bryan Bishop: This session explains how to protect transactions from changes in the Bitcoin blockchain or consensus rules, including recommendations for testing system resilience. (Video, Transcript)
For developers looking to deepen their understanding of these critical topics, 👉 explore advanced security strategies provides additional resources.
CoreDev.tech Event Highlights
CoreDev.tech is an invite-only gathering for prominent contributors to Bitcoin infrastructure projects like Bitcoin Core and the Lightning Network. While discussions were not officially recorded, Bryan Bishop compiled unofficial, rough transcripts of some sessions. Below are summaries based on transcripts from the recent event in Tokyo:
Bitcoin Optech Overview and Discussion
An introduction to Bitcoin Optech was followed by a brief discussion. The conversation then shifted to common challenges enterprises face when using Bitcoin Core and other open-source infrastructure projects. Key points included scalability, interoperability, and maintenance issues.
Using UTXO Accumulators to Reduce Data Storage Needs
Tadge Dryja presented his work on UTXO accumulators, which are functionally similar to those described in last week's newsletter but use a different hash-based construction. He further explained how these could be combined with Cory Field's UTXO Hash Set (UHO) idea. This combination would allow full nodes to store hashes of UTXOs instead of the full data, significantly reducing storage requirements for pruned nodes without necessarily requiring changes to consensus rules.
Script Descriptors and DESCRIPT Language
The default method wallets like Bitcoin Core use to monitor for transaction outputs paid to them is often described as "ambiguous, inflexible, and poorly scalable." Output Script Descriptors offer a simple language for describing scripts to wallets, making it easier to handle many common scenarios, including importing HD extended private and public keys.
Related to this is DESCRIPT, a language that uses a subset of the full Bitcoin script language to simplify the construction of certain spending policies. As explained, "We have a DESCRIPT compiler that takes what we call a policy language—AND, OR, thresholds, public keys, hash locks, time locks—and probabilities for each OR to indicate whether it's 50/50 or one side is more likely than the other, and it finds the optimal script within the defined subset." This could enable use cases like "a multisig that degrades to a weaker multisig after a period of time—for example, a 2-of-3 that after one year can be spent with just one key."
Notable Code Changes This Week
Significant updates were made to Bitcoin Core, LND, and C-lightning.
- LND #1970: The
AbandonChannelRPC method (only available in developer debug mode) now provides additional information when a user instructs their node to abandon a payment channel. Incorrect use of this method can lead to loss of funds. The new information is sufficient to allow restarting an open channel later or to prove that the program had enough data to make further commitments for a now-closed channel. - C-Lightning #2000: This update includes numerous fixes and security-related improvements for how Hash Time Locked Contracts (HTLCs) are stored in the database.
Frequently Asked Questions
What is channel splicing in the Lightning Network?
Channel splicing is a proposed feature that allows users to adjust the amount of bitcoin in a Lightning channel without closing it. This means you can add more funds to increase capacity or remove funds for use elsewhere, all while keeping the channel active for instant payments.
Why is the DESCRIPT language important for Bitcoin wallets?
DESCRIPT simplifies how wallets handle complex spending conditions. By using a subset of Bitcoin Script, it makes it easier for developers to create and manage sophisticated multi-signature or time-locked wallets without dealing with the full complexity of the script language, improving both security and user experience.
How do UTXO accumulators help with Bitcoin scalability?
UTXO accumulators allow full nodes to cryptographically commit to the set of unspent transaction outputs without storing each one in full. This can drastically reduce the storage requirements for running a node, lowering the barrier to entry and helping the network become more decentralized and scalable.
What was the main focus of the Edge Dev++ security talks?
The talks focused on practical security measures for businesses and individuals. Key topics included securing exchange platforms, best practices for wallet key management using hardware security modules (HSMs), and strategies for handling blockchain reorganizations and potential forks.
Where can I learn more about implementing these advanced Bitcoin features?
For a comprehensive guide on implementing these and other cutting-edge Bitcoin and Lightning Network features, 👉 discover expert development resources offers a curated list of tools and documentation.