Comment by segmondy | Hacker News Reader

Comment by segmondy | Hacker News Reader

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I don't know how Google solved this, but it's an old solution. Shamir secret sharing. You break apart your keys into M pieces, where you need N pieces to reconstruct the key, so let's say 3/8. Then you need 3 pieces out of the 8 pieces it's broken into to recover your key. You take each of those 8 pieces and give to trusted sources. When you need to reconstruct your key, you have at least 3 of those give you the key and you recover.

How does this look in implementation. When I Implemented this in multipasskey (YC demo). It would ask you to select contacts you trusted. Then it would send the sharded parts of the key in the background to them. If you need to recover, you make a request to them. It would reconstruct your device key when you got enough pieces. Once you have your device key, it would download your encrypted backup of keys from the remove server and you are back as new.

I called my project multipasskey in 2017/2018 and applied to YC with a working demo and they said nope. I'm going to assume that I sucked at selling it. ;-)

I had the same idea about a decade ago but never bothered to try to implement it. I felt like it would have suffered from the same problem all other technologies have in security: overly complex user interactions. The concept makes sense, but getting N other people to commit is overhead the average user probably doesn't want to deal with.

So I preferred the idea of regular folks for backup, for security reasons. I thought of the idea of professional users like say your bank or 3rd party. The issue is that it's far easier for the govt to subpoena those pro 3rd parties and recover your key. Whereas, they would have to know which of your friends you used for key recovery to be able to do that. The idea was to make it tough for a bad/powerful actor to steal your key. Of course, the challenge is that a non social person would need friends or to depend on ISPs, banks (pro 3rd party providers). My goal besides security when building this project was to break the chain of 3rd party auths (Google, MS, Github, etc) :-(. They use their auth as a way to lock folks into their ecosystem and if you offend them in anyway, you could lose access to everything. Offend Google on adsense and lose your personal photos/email. Offend Amazon on sales and lose your prime streaming/AWS access. Hopefully as the idea picks up, the monopolistic corps can be tackled again to remove such power.

I wholeheartedly agree with where you were aiming your goals. Other thoughts I've had:

- What if access is time critical but your backup people are distributed across timezones? Or they aren't available for some reason? Could be hours to days before you could recover your account

- Adding/removing people as they enter/exit your life could make it a challenge to maintain (PGP + trust vibes)

Now there is a technically savvy solution that is a technical tour-de-force.

Very very cool.

But also completely unrealistic for the average person to use.

How? The usage was very easy. You select a contact and add them as your recovery contact (by selecting contact from your contact list) The system adds the key in the background. If they don't have the app, the app asks you to tell them to install the app (viral growth?). The users didn't need to know any thing technical. But install app, and click yes/no like they do with a 2FA app.

I think the challenge is more coordinating the 8 people who will be a trusted part of your life long-term. Also they’d have to be sure to keep their fragments of the key intact through replacing devices, etc, no? Seems like just keeping a Yubikey in a safe deposit box would be simpler.

if they replaced their device, their new device would still preserve your key, just like you replacing your device keeps your key.

Define ‘safe deposit box’?

If it is a safe at your home, you need to have a fixed home address in the first place, and the usual advice about off-site backups also applies.

If it is at friends or family, you’re back at the same problem.

If it is a rented deposit box, you need to trust the company you rent it from (banks don’t usually offer such services anymore, and there are risks like in [1])

[1] https://www.nytimes.com/2019/07/19/business/safe-deposit-box... (archive: https://archive.is/7qbkR)

I don't have eight people, what then?

You use different numbers, for example 3/5 or 2/3.

You have to have at least 3 peers, though (IIRC, 2/3 is the minimum split possible that would provide fault tolerance).

I’m not in the crypto world to know why this is the way it is, but if you only need 3 pieces out of the 8 to reconstruct the key, why split it into 8? Is it to have a larger pool should you need it/higher odds of being able to gather 3 should some pieces be lost?

Sounds like a great idea. Sometimes it's hard to be so in tune with the technology, and also be the salesperson!

Added bonus you can’t die unless someone locates each piece and destroys them all

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