This week’s newsletter suggests an update for C-Lightning users, describes a discussion about BIP69 deterministic input/output ordering on the mailing list, notes public overt ASICBoost support is available for miners using Antminer S9, and provides links to resources about both Square’s open sourced Subzero HSM-based multisig cold storage solution and the recent Lightning Network Residency and Hackday in New York City. Also included are selected recent Q&A from Bitcoin StackExchange and descriptions of notable code changes in popular Bitcoin infrastructure projects.

● BIP69 discussion: this BIP from 2015 adopted by several notable wallets specifies an optional method for deterministically ordering inputs and outputs within a transaction based on the public contents of the transaction. However, other wallets have not adopted it (or even rejected it as unsuitable for adoption), leading perhaps to a “worst of both worlds” situation where wallets using BIP69 can be fairly easily identified and so wallets not using BIP69 may also be easier to identify by negation. In this thread to the Bitcoin-Dev mailing list, Ryan Havar suggests that one reason wallet authors like BIP69 is that its deterministic ordering makes it easy and fast for their tests to ensure that they haven’t leaked any information about the source of their inputs or the destination of their outputs (e.g. in some old wallets, the fist output always went to the recipient and the second output was always change—making coin tracking trivial). Havar then suggests an alternative deterministic ordering based on private information that would be available to the test suite but not exposed by production wallets, allowing developers who want to thwart block chain analysis—but also have simple and fast tests—to migrate away from BIP69.

● Overt ASICBoost support for S9 miners: support for this efficiency-improving feature was announced by both Bitmain and Braiins this week. ASICBoost takes advantage of the fact that the SHA256 algorithm used in Bitcoin mining first splits the 80 byte block header into 64 byte chunks. If a miner can find multiple proposed block headers where the first chunk of 64 bytes are different but start of the next chunk of 64 bytes are the same, then they can try different combinations of the first chunk and second chunk to reduce the total number of hashing operations they need to carry out to find a valid block. Early estimates indicate an improvement of 10% (or perhaps more) on existing Antminer S9 hardware. The overt form of ASICBoost alters the versionbits field in the block header, which can cause programs such as Bitcoin Core to display a warning such as “13 of last 100 blocks have unexpected version”. Some ASICBoost miners have voluntarily restricted their altered versionbits range to that defined by BIP320, giving future programs the option to ignore those bits for upgrade signaling.