This week’s newsletter requests testing of the C-Lightning and Bitcoin Core release candidates, invites participation in structured review of the taproot proposal, highlights updates to two Bitcoin wallets, and describes a few notable changes to popular Bitcoin infrastructure projects.

Action items

  • Help test release candidates: experienced users are encouraged to help test the latest release candidates for the upcoming versions of Bitcoin Core and C-Lightning.


  • Taproot review: starting the first week of November, several Bitcoin contributors will be hosting a series of weekly meetings to help guide people through review of the proposed bip-schnorr, bip-taproot, and bip-tapscript changes. All developers, academics, and anyone else with technical experience are welcome. The expected commitment is four hours a week for seven weeks, with one hour each week being a group meeting and the other three hours being your own independent review of the proposals. In addition to review, developers will be encouraged to optionally implement a proof-of-concept that either shows how schnorr or taproot can be integrated into existing software or that demonstrates the new or improved features the proposals make possible. This will help implementers to identify flaws or sub-optimal requirements in the current proposals that might be missed by people who only read the documentation.

    The ultimate goal of the review is to allow participants to gain enough technical familiarity with the proposals to be able to either vocally support the proposals, advocate for changes to the proposals, or clearly explain why the proposals shouldn’t be adopted into the Bitcoin consensus rules. Adding new consensus rules to Bitcoin is something that should be done carefully—because it can’t be undone safely for as long as anyone’s bitcoins depend on those rules—so it’s in every user’s interest that a large number of technical reviewers examine the proposals for possible flaws before they are implemented and before users are asked to consider upgrading their full nodes to enforce the new rules. Whether through this organized review or in some other way, Optech strongly encourages all technically skilled Bitcoin users to dedicate time to reviewing the taproot set of proposals.

    Anyone wanting to participate should RSVP soon so that the organizers can estimate the total number of participants and start forming study groups. To register or learn more, please see the Taproot Review repository.

Changes to services and client software

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

  • Electrum Lightning support: In a series of commits this month, Electrum has merged support for Lightning Network into master. A presentation deck titled Lightning Implementation in Electrum by Thomas Voegtlin provides some background information and screenshots.

  • Blockstream Green Tor support: Version 3.2.4 of the Blockstream Green Wallet adds built-in Tor support for both iOS and Android. While Tor was supported in previous Android versions, it required a separate application whereas both Android and iOS versions are now bundled with Tor support.

Notable code and documentation changes

Notable changes this week in Bitcoin Core, C-Lightning, Eclair, LND, libsecp256k1, Bitcoin Improvement Proposals (BIPs), and Lightning BOLTs.

  • C-Lightning #3150 adds new signmessage and checkmessage RPCs. The first RPC will sign a message that can be verified by someone with your LN node’s public key. The second RPC will verify a signed message from another node either using a pubkey provided by the user or by confirming the message is signed by a pubkey belonging to any known LN node (e.g. a node in the set returned by the listnodes RPC).

  • LND #3595 raises the default maximum CLTV expiry from 1,008 blocks (about 1 week) to 2,016 blocks (about two weeks). This is the maximum amount of time a new payment can be stuck as pending before it can be reclaimed by its spender. LND recently tried to keep this at 1,008 blocks by decreasing the CLTV delta—the minimum number of blocks each routing node along the payment path will have to claim its particular payment—from 144 blocks to 40 blocks (see Newsletter #40) but older LND nodes and some other implementations have continued to use 144 as their default. If each hop requires a delta of 144, the new maximum expiry of 2,016 makes the maximum-length routing path about 14 hops.

  • LND #3597 reverts the migration policy described in Newsletter #64 where LND could only be upgraded from a maximum of one major release back. The PR for the reversion notes, “the prior stricter policy created a large burden on applications that package lnd as they’re forced to deploy special code to handle certain upgrade paths. In addition, it was realized that the policy was most damaging to mobile deployments as it’s customary for users to skip versions, making the stricter upgrade policy difficult to manage without dramatically affecting the end user.”