This week’s newsletter describes the results of discussion about choosing activation parameters for a taproot soft fork and includes our regular sections with selected questions and answers from the Bitcoin Stack Exchange, releases and release candidates, and notable changes to popular Bitcoin infrastructure software.

News

  • ● Taproot activation discussion: Michael Folkson summarized a second meeting about activation parameters for taproot, concluding that “there wasn’t overwhelming consensus for either LOT=true or LOT=false”, the LockinOnTimeout (LOT) parameter from BIP8 that determines whether or not nodes will require mandatory signaling for activation of the fork. However, there was nearly universal agreement on other activation parameters, most notably reducing the amount of hash rate that needs to signal for the fork to activate from 95% to 90%.

    Discussion continued about the LOT parameter on the mailing list, mainly about the effect of encouraging users to choose the option themselves, either via a command line option or by choosing what software release to use. No clear agreement was reached as of this writing and there does not seem to be a widely supported path forward to activating taproot—even though taproot itself appears to be almost entirely desired.

Selected Q&A from Bitcoin Stack Exchange

Bitcoin Stack Exchange is one of the first places Optech contributors look for answers to their questions—or when we have a few spare moments to help curious or confused users. In this monthly feature, we highlight some of the top-voted questions and answers posted since our last update.

  • ● Is sharding a good alternative to multisig? User S.O.S asks about the viability of a sharding scheme like Shamir’s Secret Sharing (SSS) to achieve multisig-like capabilities. Pieter Wuille notes the advantages of OP_CHECKMULTISIG over SSS (accountability, no need to reconstruct the secret key on one machine), advantages of SSS over OP_CHECKMULTISIG (less fees, more privacy), and schnorr considerations (lack of accountability, no need to reconstruct the secret key on one machine, less fees, more privacy, additional complexity).

  • ● Can a channel be closed while the funding tx is still stuck in the mempool? After attempting to open an LN channel but setting the funding transaction’s feerate too low, PyrolitePancake asks about closing the channel while the funding transaction remains in the mempool. While one option is to pursue opening the channel by waiting for confirmation and potentially rebroadcasting the transaction, Rene Pickhardt notes that double spending the funding transaction’s inputs would drop it from mempools. Some sample commands are provided by cdecker for C-lightning to either rebroadcast the funding transaction or create a double spend.

  • ● With peerblockfilters=1 hundreds of “btcwire 0.5.0/neutrino” connections are downloading TB from my Bitcoin node While running Bitcoin Core 0.21.0 with compact block filters enabled, qertoip notices a large number of connections (75%) and bandwidth usage (90%) from btcwire 0.5.0/neutrino user agents. Murch points out that these peers are LND nodes and because compact block filters are both a new feature of Bitcoin Core as well as disabled by default, there may be a lack of compact block filter serving peers on the network currently resulting in higher traffic to nodes supporting the filters.

  • ● Is there dumpwallet output documentation & explanation? Andrew Chow uses the answer as an opportunity to provide additional documentation and explanation of the dumpwallet RPC’s output.

  • ● Is there something about Bitcoin that prevents implementing the same privacy protocols of Monero and Zcash? Pieter Wuille lists a few challenges of why developers might not choose to work on, and the ecosystem might not choose to support, the approaches to privacy that Monero or Zcash have taken. Considerations include downsides to an “opt-in” approach, introduction of new cryptographic security assumptions, scalability concerns, and the problem of supply auditability.

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 0.12.1-beta is the latest maintenance release of LND. It fixes an edge case that could lead to accidental channel closure and a bug that could cause some payments to fail unnecessarily, plus some other minor improvements and bug fixes.

Notable code and documentation changes

Notable changes this week in Bitcoin Core, C-Lightning, Eclair, LND, Rust-Lightning, libsecp256k1, Hardware Wallet Interface (HWI), Rust Bitcoin, BTCPay Server, Bitcoin Improvement Proposals (BIPs), and Lightning BOLTs.

  • ● Bitcoin Core #19136 extends the getaddressinfo RPC with a new parent_desc field that contains an output script descriptor for a wallet containing the address’s public key. The wallet’s BIP32 path will have all hardened prefixes stripped so that only public derivation steps remain, allowing the descriptor to be imported into other wallet software which can monitor for bitcoins received to the address and its sibling addresses.

  • ● Bitcoin Core #15946 makes it possible to simultaneously use both configuration options prune and blockfilterindex to maintain compact block filters on a pruned node (also serving them if the peerblockfilters configuration option is used). An LND developer indicated that this would be beneficial for their software, and it could also allow a future update that allows the wallet logic to use the block filters to determine which historic blocks the pruned node needs to re-download in order to import a wallet.

  • ● Eclair #1693 and Rust-Lightning #797 change how node address announcements are handled. The current BOLT7 specification requires the sorting of addresses within an announcement, however some implementations were not using or enforcing this rule. Eclair updated their implementation to begin sorting and Rust-Lightning updated their implementation to stop requiring the sorting. A PR is open to update the specification but it is still under discussion exactly what change should be made.

  • ● HWI #454 updates the displayaddress command to add support for registering multisig addresses on a BitBox02 device.

  • ● BIPs #1052 assigns BIP338 to the proposal to add a disabletx message to the Bitcoin P2P protocol. A node that sends this message during connection establishment signals to its peer that it will never request or announce transactions on that connection. As described in Newsletter #131, this allows peers to use different limits for disabled relay connections, such as accepting additional connections beyond the current 125 connection maximum. See also the discussion summary from the January 12th P2P developers meeting.