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I wrote a post at the start of last year thinking about my general priorities for Bitcoin and I’m still pretty happy with that approach — certainly “store of value” as a foundation feels like it’s held up!

I think over the past year we’ve seen a lot of people starting to hold a Bitcoin balance, and that we’ll continue to do so — which is a win, but following last year’s logic also means we’ll want to start paying more attention to the later parts of the funnel as well: if we (for instance) double the number of people holding Bitcoin, we also want to double the number of people doing self-custody, and double the number of people transacting over lightning, eg; and ideally we’d want that in addition to whatever growth in self-custody and layer 2 transactions we’d already been aiming for if Bitcoin adoption had remained flat.

That said, I’m not sure I’m in a growth mindset for Bitcoin this year, rather than a consolidation one: consider the BTC price at the start of the past few years: 2016: ~$450, 2017: $1000, 2018: $13,000, 2019: $3700, 2020: $8000, 2021: $30,000. Has there been a 8x increase in security and robustness during 2016, 2017 and 2018 to match the 8x price increase from Jan 2016 to Jan 2019? Yeah, that’s probably fair. Has there been another 8x increase in security and robustness during 2019 and 2020 to match the 8x price increase there? Maybe. What if you’re thinking of a price target of $200,000 or $300,000 sometime soon — doesn’t that require yet another 8x increase in security and robustness? Where’s that going to come from? And those 8x factors are multiplicative: if you want something like $250k by December 2021, that’s not a “three-eights-are-24” times increase in robustness over six years (2016 to 2022), it’s an “eight-cubed-is-512” times increase in robustness! And your mileage may vary, but I don’t really think Bitcoin’s already 500x more robust than it was five years ago.

So as excited as I am about taproot and the possibilities that opens up (PTLCs and eventually eltoo on lightning, scriptless scripts and discreet log contracts, privacy preserving proof of reserves, cheap multisig — the list might not be infinite but at least seems computationally intractable), I think I’m now even more of the view that it’s probably more important to work on things that reinforce the existing foundations, than neat new ideas to change them than I was this time last year.

There are already a bunch of areas where Bitcoin’s approach to security and robustness has improved technically over the past few years: we’ve got more people doing reviews (eg, via the PR review club, or getting introduced to Bitcoin via the Chaincode Residency etc), we’ve got deeper and more diverse continuous integration testing (thanks both to more integrations being enabled via github, and travis becoming unreliable enough to force looking at other approaches), fuzz testing has improved a lot and become a bit more broadly used, and I think static analysis of the codebase has improved a bit. There have been a bunch of improvements in code standards (eg using safe pointers, locking annotations, spans instead of raw pointers) too, I think it’s fair to say. I haven’t done an analysis here, just going from gut feel and recollection.

With a focus on robustness, to me, the areas to prioritise in the short term are probably:

Modularisation — eg, so that we can better leverage process separation to reduce security impacts, and better use fuzz testing to catch bugs in edge cases. There’s already work to split the gui and wallet into separate processes, though while that’s merged, it’s not part of the standard build yet. Having the p2p-network-facing layer also be a separate process might be another good win. While it’s a tempting goal, I think libconsensus is still a ways off — p2p, mempool management, and validation rules are currently pretty tightly coupled — but there’s steps we can make towards that goal that will be improvements on their own, I think. The P2P network — This is the obvious way to attack Bitcoin since by its nature everyone has access to it. There are multiple levels to this: passively monitoring the p2p network may allow you to violate users’ privacy expectations, while actively isolating users onto independent networks can break Bitcoin’s fundamental assumptions (you can’t extend the longest chain if you can’t communicate with any of the people who have the longest chain). There are also plenty of potential problems that someone could cause in between those extremes that could, eg, break assumptions that L2 systems like lightning make. Third-party (potentially centralised) alternatives as backups for the p2p network may also be valuable support here — things like Blockstream Satellite, or block relay over ham radio, or headers over DNS: those can mend splits in the p2p network that the p2p layer itself can’t automatically fix. Or efficiency improvements like erlay or block-relay-only can allow a higher degree of connectivity making attacks harder. CI, static analysis, reproducible builds — Over the past year, travis seems like it’s gone from having the occasional annoying problem to being pretty much unusable for open source projects. CI is an important part of both development and review; having it break makes both quite a lot harder. What we’ve got at this point seems pretty good, but it’s new and not really time-tested yet, so I’d guess a year of smoothing out the rough edges is probably needed. I think there’s other “CI”-ish stuff that could be improved, like more automated IBD testing (eg, I think bitcoinperf is about 3 months out of date). Static analysis serves a similar goal to tests in a different way; and while we’ve already got a lot of low hanging fruit of this nature already integrated into CI via linters and compiler options, I suspect there’s still some useful automation that could happen here. Finally, nailing down the last mile to ensure that people are running the software the devs are testing is always valuable, and I think the nixos work is showing some promise there. Third-party validation — We’ve had a few third-party monitoring tools arise lately — various sites monitoring feerate and mempool sizes, forkmonitor checking for stale blocks (and double-spends), or, at a stretch, optech’s reviews of wallet behaviour and segwit support. There’s probably a lot of room for more of this. I’d love to list formal verification at the consensus layer as a priority, but I think there’s too much yak-shaving needed first: it would probably need all the refactoring to get to libconsensus first, then would likely need that separated into its own process, which you could only then start defining a formal spec for, which in turn would give you something you could start doing formal verification against. I suspect we’ll want to be at that point within another cycle or two though.

I’m not concerned about mining — eventually there might be a risk that the subsidy is too small and there’s not enough fee income, but that’s not going to happen while the price doubles faster than the pre-scheduled halvings. There’s certainly centralisation risks, whether in ASIC manufacture, in hardware ownership/control, or at the pool level, but my sense of things is that’s not getting worse, and is not the biggest immediate risk. Maybe I’m wrong; if so, hopefully the people who think so are working on preventing problems from arising, rather than taking advantage of them.

There are other levels of robustness and security beyond just “keep the network working”, if you consider the question of “how to prevent my coins from being lost/stolen?” more broadly. The phishing attacks and potential for physical attacks resulting from the Ledger leak are an easy example of a problem of this sort, but exchange hacks/failures in general, malware swapping addresses so your funds go to an attacker instead of the intended recipient, and lost access to keys are also pretty bad. I think descriptors, miniscript and taproot multisig probably provide for a good path forward to help prevent losing access to keys; and it’s possible that progress on BIP322 (signing messages against a Bitcoin address) may provide a path to avoiding address swapping attacks.

Technical solutions are, in some sense, all you can hope for if you’re doing self-custody; but where a bank/custodian is involved (good) regulation might be useful too: requirements to keep customer data protected or destroyed, third-party audits to ensure the best-practices procedures you’re claiming to follow are actually being followed, etc. If custodians store funds in taproot addresses, it may be feasible to do privacy preserving (zero-knowledge) proofs of solvency, eg, making it harder for fly-by-night folks to run ponzi schemes or otherwise steal their customers’ funds.

Obviously where possible these sorts of standards should be implemented via audited open source code rather than needing extensive implementation costs by each company. But one other thing to think about is whether regulations of this nature could be setup as industry standards (“we comply with the industry standard, competitor X doesn’t”) rather than necessarily a government regulator — for one, it certainly seems questionable whether government regulators have the background to pick good best practices for cryptocurrency systems to follow. Though perhaps it would be to have something oriented towards “consumer rights” than “industry” per se, to avoid it just being a vector for regulatory capture.