This week’s newsletter announces a project to create a BIP324 proxy for light clients and summarizes discussion about a proposed BTC Lisp language. Also included are our regular sections describing recent changes to clients and services, announcing new releases and release candidates, and summarizing notable changes to popular Bitcoin infrastructure software.


  • BIP324 proxy for light clients: Sebastian Falbesoner posted to Delving Bitcoin to announce a TCP proxy for translating between the version 1 (v1) Bitcoin P2P protocol and the v2 protocol defined in BIP324. This is especially intended to allow light client wallets written for v1 to take advantage of v2’s traffic encryption.

    Light clients typically only announce transactions belonging to their own wallets, so anyone capable of eavesdropping on an unencrypted v1 connection can reasonably conclude that a transaction sent by a light client belonged to someone using the origin IP address. When v2 encryption is used, only the full nodes receiving the transaction will be able to definitively identify it as originating from the light client’s IP address, assuming none of the light client connections is subject to a man-in-the-middle attack (which is possible to detect in some cases and which later upgrades may automatically defend against).

    Falbesoner’s initial work pulls together BIP324 functions written in Python for Bitcoin Core’s testing suite, which results in a proxy that is “terribly slow and vulnerable to side-channel attacks [and] not recommended to use it for anything but tests right now”. However, he is working on rewriting the proxy in Rust and may also make some or all of its functions available as a library for light clients or other software that wants to natively support the v2 Bitcoin P2P protocol.

  • Overview of BTC Lisp: Anthony Towns posted to Delving Bitcoin about his experiments over the past couple of years creating a variant of the Lisp language for Bitcoin, called BTC Lisp. See Newsletters #293 and #191 for previous discussions. The post goes into significant detail; we encourage anyone interested in the idea to read it directly. We will briefly quote from its conclusion and future work sections:

    “[BTC Lisp] can be a little expensive on-chain, but it seems like you can do pretty much anything […] I don’t think implementing either a Lisp interpreter or the bucket of opcodes that would need to accompany it is too hard [but] it is pretty annoying to write Lisp code without a compiler translating from a higher level representation down to the consensus-level opcodes, [though] that seems solvable. [T]his could be taken further [by] implementing a language like this and deploying it on signet/inquisition.”

    Russell O’Connor, developer of the Simplicity language that may also one day be considered as an alternative consensus scripting language, replied with some comparisons between Bitcoin’s current Script language, Simplicity, and Chia/BTC Lisp. He concludes, “Simplicity and the clvm [Chia Lisp Virtual Machine] are both low level languages that are meant to be easy for machines to evaluate, which causes tradeoffs that make them hard for humans to read. They are intended to be compiled from some different, human-readable, non-consensus-critical language. Simplicity and the clvm are different ways of expressing the same old things: fetching data from an environment, tupling up bits of data, running conditional statements, and a whole bunch of primitive operations of some sorts. […] Since we want this [split between efficient low-level consensus language and high-level non-consensus comprehensible language] regardless, the details of the low-level language become somewhat less important. I.e., with some effort, your high level BTC lisp language could probably be translated/compiled to Simplicity […] Similarly, wherever the design of [Simplicity-based] Simphony [high-level non-consensus language] ends up, it can probably be translated/compiled [to] your low level BTC lisp language, with each translator/compiler language pair offering different potential complexity/optimization opportunities.”

Changes to services and client software

In this monthly feature, we highlight interesting updates to Bitcoin wallets and services.

  • BitGo adds RBF support: In a recent blog, BitGo announced support for fee bumping using replace-by-fee (RBF) in their wallet and API.

  • Phoenix Wallet v2.2.0 released: With this release, Phoenix can now support splices while making LN payments using the quiescence protocol (see Newsletter #262). Additionally, Phoenix improved the swap-in feature privacy and fees by using their swaproot protocol.

  • Bitkey hardware signing device released: The Bitkey device is designed to be used in a 2-of-3 multisig setup with a mobile device and a Bitkey server key. Source code for the firmware and various components are available under a Commons Clause modified MIT License.

  • Envoy v1.6.0 released: The release adds features for fee bumping transactions as well as canceling transactions, both enabled using replace-by-fee (RBF).

  • VLS v0.11.0 released: The beta release allows multiple signing devices for the same Lightning node, a feature they call tag team signing.

  • Portal hardware signing device announced: The recently announced Portal device works with smartphones using NFC with hardware and software source available.

  • Braiins mining pool adds Lightning support: The Braiins mining pool announced a beta for mining payouts through Lightning.

  • Ledger Bitcoin App 2.2.0 released: The 2.2.0 release adds miniscript support for taproot.

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.

  • Bitcoin Core 26.1rc2 is a release candidate for a maintenance release of the network’s predominant full node implementation.

  • Bitcoin Core 27.0rc1 is a release candidate for the next major version of the network’s predominant full node implementation.

Notable code and documentation changes

Notable recent changes in Bitcoin Core, Core Lightning, Eclair, LDK, LND, libsecp256k1, Hardware Wallet Interface (HWI), Rust Bitcoin, BTCPay Server, BDK, Bitcoin Improvement Proposals (BIPs), Lightning BOLTs, Bitcoin Inquisition, and BINANAs.

Note: the commits to Bitcoin Core mentioned below apply to its master development branch and so those changes will likely not be released until about six months after the release of the upcoming version 27.

  • Bitcoin Core #27375 adds support to the -proxy and -onion features for using Unix domain sockets rather than local TCP ports. Sockets can be faster than TCP ports and offer different security tradeoffs.

  • Bitcoin Core #27114 allows adding “in” and “out” to the whitelist configuration parameter to give special access to particular incoming and outgoing connections. By default, a peer listed in the whitelist will only receive special access when it connects to the user’s local node (an incoming connection). By specifying “out”, the user can now ensure a peer receives special access if the local node connects to it, such as by the user calling the addnode RPC.

  • Bitcoin Core #29306 adds sibling eviction for transactions descended from an unconfirmed v3 parent. This can provide a satisfactory alternative to CPFP carve-out, which is currently used by LN anchor outputs. V3 transaction relay, including sibling eviction, is not currently enabled for mainnet.

  • LND #8310 allows the rpcuser and rpcpass (password) configuration parameters to be retrieved from the system environment. This can allow, for example, a lnd.conf file to be managed using a non-private revision control system without storing the private username and password.

  • Rust Bitcoin #2458 adds support for signing PSBTs that include taproot inputs.