Reimplement TXQR in Rust

[burdges]

We want an implementation of TXQR in Rust for Parity signer and probably subkey. We'd encourage some public discussion of the exact design features of TXQR, since maybe we'd find some small improvements.

maciejhirsz/uos#7
novasamatech/parity-signer#457
novasamatech/parity-signer#320

[Slesarew]

Now we have an MWP!

Receiving end

Parity Signer now allows metadata transfer through this PR (if/when it's merged, that is):
novasamatech/parity-signer#743

Front-end and native component interactions are hidden in react-native, logic is in rust. To test, press the menu button in top-right corner, navigate to network settings, select any substrate-based network (for example, westend), scroll down to "manage metadata" button, then select scanner in the middle on the bottom. Begin scanning, you can skip frames, re-focus and have shaky hands.

Transmitting end

Transmitting end generating apng written in Rust:
https://github.com/paritytech/rtxqr

The example transferable metadata is attached. Message format adheres to still not accepted but proposed format:
https://github.com/Slesarew/uos

That is, actual metadata is prefixed with 530080

I'm looking for further suggestions, current plan includes replacing all Signer transactions with raptorq fountains (or at least all multiframe ones) and maybe I should make a separate app to send apks to upgrade things over the airgap - maybe we should develop a general standard for that?

If there is a demand, I could try to write rust-based native scanner component callable from RN, but this will have longer ETA and I'm not sure it is all that needed.

[burdges]

Very cool! Yes, any multi-frame tx should becomes more user friendly using raptorq, although maybe keep an eye out for regressions at small numbers like two frames or whatever.

We bite off larger obligations ala https://github.com/heartsucker/rust-tuf if we start doing upgrades, since a malicious apk might reactivate the wifi or whatever. I'd expect it'd take too long via QR code anyways though. I'd instead think people could use memory cards,

[burdges]

As an aside, we'll try to make some progress on w3f/schnorrkel#11 soon-ish, which should be interesting for parity signer. Feel free to chat with me about it on Element.

[Slesarew]

I'd instead think people could use memory cards,

This does not really fix malicious apk hazard, but any updates without full phone wipe are hazardous in fact.

The only safe alternative might be with memory cards, but in that case the card should be physically destroyed after update, otherwise this will not be safe. If we follow this path, we'll probably need to post safe memory card destruction protocols so that people don't hurt themselves and at the same time complete the task securely with little effort.