Bitcoin Core Wishlist

Bitcoin Core Wishlist

I started to contribute code and reviews to Bitcoin Core a few months ago and gradually accumulated lists of stuff I’d like to see. Some of these I can do myself, others are still beyond my level of expertise, still others might be terrible ideas and never happen.

A note on process

Just to make it abundantly clear: this is my personal wish list, not anyone’s roadmap. There is no roadmap, there’s just stuff in progress. Every contributor has their own things they’re working on, their own set of priorities.

A pull request generally gets merged if and only if:
1. it has received enough review, by relevant experts; and
2. there are no unresolved objections, e.g.
a) it is of sufficient quality;
b) it doesn’t break things;
c) it doesn’t cause more problems than it solves

Criterion (2) is easiest to deal with as a developer: if someone reviews your code and they find a problem, either fix it or explain why it’s not actually a problem. There are also automated tests and other (e.g. formatting) checks that save reviewers time. It’s not uncommon to revise a pull request a dozen times until it’s good enough.

Criterion (1) can be a bottleneck. If helps to work on stuff you know other developers care about. Hence this list; if you work on anything on this list, or stuff that indirectly makes this list more likely to move forward, your chances of me reviewing your code increase.

There’s other ways to increase the chance of getting your code reviewed. Keep changes small and focussed. The more stuff you change in a single pull request, the more difficult it becomes to review and the fewer developers even have the prerequisite knowledge to understand all of it. Use a clear title and description, add a screenshot if it’s a UI change, and keep these up to date when you change things.

In order to keep things moving after the first feedback you receive, it helps to actually address that feedback and to do so quickly, as this motivates reviewers. Even the most experience Core developers sometimes have to wait up to a year to get stuff merged, so patience is useful.

Anyway, here’s my list:

Better Replace-By-Fee UI

People may forgotten the days of high fees, but those days will probably return some day. If you’re not in a hurry to send a transaction it’s a good idea to set a low fee. However, that may cause it to get stuck, especially if fees rise after you send it.

Use a low fee if you’re not in a hurry.

If a transaction gets stuck, you can replace it with a transacion that pays a higher fee. Just right-click on it and select Increase Transaction Fee, et voila:

Use a low fee if you’re not in a hurry.

Unfortuately this UI is rather inflexible. It doesn’t let the user specify the new fee, nor provide any hint what a good amount would be. Due to implementation details the fee can’t be more than the change amount of the original transaction (and doesn’t work if the original transaction doesn’t have a change address), a restriction that’s hard to explain to the user.

The solution probably consists of automatically adding new inputs to the transaction as needed, as well as reusing the existing fee recommendation UI.

We could go beyond that, e.g.

  • pre-generate a series of transactions with escalating fees, so that a user can specificy a deadline and maximum fee. The wallet would then broadcast these as the deadline approaches
  • append new transactions to existing unconfirmed transactions
  • peer2peer mixing, i.e. mempool compression (kidding… or am I?)

Needless to say, all the above is surprisingly non-trivial and there’s some privacy issues and safety gotcha’s as well.

An additional complexity here is that the GUI and RPC have different ways of composing a transaction, which could lead to duplicate work.

Hardware Wallet

Hardware wallets like the Ledger Nano S keep your private keys very safe, but they rely on a web based backend to show your balance and compose transactions. Only signing happens on the device. This is not ideal for privacy and if their servers disappear you most likely have to fall back to paper backups.

At the same time, Bitcoin Core saves your private keys on your machine

So I’d like to be able to use a hardware wallet directly with Bitcoin Core.

User friendly backup and recovery

Most consumer wallets nowadays tell the user to write down a 12–24 word phrase and keep it somewhere save. They also tend to strongly remind users to do so. Bitcoin Core does have backup functionality and it’s present in the UI, but I’m not sold on it. I haven’t had a chance to really dig into this topic, so I’ll keep this section vague.

More broadly, I have a seperate wish list of stuff I’d like to see improved around recovery phrases and hierarchical deterministic wallets.

Prune UI

Github issues: #6461, #12404

I suspect more people would run a full node if they knew it didn’t eat 180 GB of their precious hard disk space. It’s trivial to enable pruning, i.e. just open bitcoin.conf, add prune=10000 and restart to prune to ~10 GB. However I’d like to lower that barrier even further, e.g. by having the wallet check the users disk space on first launch. If it’s not huge, propose some reasonable number.

A related issue is that pruned nodes currently are quite slow to sync due to implementaiton details, but that should be easy to solve.

Somewhat related, performance is still not great for non-SSD drives: #12058.

Run full node on iPhone X

Whether or not it’s useful remains to be determined, but I bought an iPhone X with 256 GB of storage, which means it fits the entire blockchain. That’s enough reason for me to want to run a full node on it, but I need some help figuring out build pipeline magic and getting it to interact with an iOs app.

Fiat amounts

This is probably a bit controversial, but I as long as other people in the real world use things like euros, I’d like to be able to see how much I’m about to send in fiat terms. However you can’t just fetch a price feed from an external website. For example that would reveal the users IP, which combined with the timing of requests could be enough to reveal a users addresses. Then there’s the issue of which price to trust. But now I find myself googling conversion rates for the exact amount I’m about to send, which can’t possibly be good for my privacy. 🙂 Any creative solutions out there?

Easier deterministic (Gitian) builds and verification

How do you know the program you downloaded is actually based on the Bitcoin Core source code? Every release a number of developers make a deterministic build and publicly attest to it. It’s getting easier for more developers to do so. There’s probably enough eyes on this to make that any funny business with the public release would be caught, but perhaps not for indiduals to see if they’re indivually targetted.

This is already a huge improvement over the pervasive App Store model where you just blindly trust Apple, Google or Microsoft to not mess with the software, which they automatically update, while you’re logged into an account with them that has all your personal details. However I think this process — of developers publicly comitting to specific source code for every update, and each computer verifying this — should be the norm for all software, and for that it needs to be made much easier.

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