You can store it in two or N places. Or bank can do this for you.

More places is more opportunities for the baddies to get it.

Shamir it.

please wrap the whole thing as a trustworthy product

I don't understand why this was downvoted. In case it's not clear: (S)he's saying to split the key into multiple shares that can be used to reconstruct the key if you have a large enough quorum. Then store each share in a different place. As long as you don't lose too many of the shares, you'll be fine. And one baddie is NOT enough to get the key.

Either shuffling those keys stored in N different deposit boxes is overly complicated for a normal person, or it is not overly complicated for a moderately dedicated baddie either

Unless the "baddie" in this case is the government, why would it be easy for anyone to obtain access to multiple secrets stored in multiple boxes/banks?

Multisig is a pretty common setup for crypto and there is software that makes it easier.

Can you show how it can be easy to use in normal life for a regular person and at the same time really difficult for the attacker?:)

"Mom, I already told you: you have to generate a key pair, split the private key into three parts using Shamir' secret sharing algorithm, then give each part to three banks. Whenever you want to use it, you have to go collect it from each of those banks---but DON'T write it down anywhere---and perform your transaction"

And to think the conversation started with an observation that people can't even remember one password.

I agree, there's miles of runway remaining for improving the UX. I actually think it'd be neat if a crypto had this (and a few other things) as a baked-in feature. i.e. In order to create a wallet in the first place, you need to identify e.g. 5 trusted friends who'll serve as recovery partners. Maybe it's initially tied to the same invite mechanic used to join the ecosystem. Could be done in a privacy-preserving (and to some degree anonymity-preserving) fashion. The right UI could make this even simpler than recovering a Gmail account. Everyone would just have it set up, and these conversations about losing your keys would be a relic of the past.

"soerxpso" said "store your key at the bank", but you are saying "two or N places". So it sounds like 1 bank is less secure for your key then 1 bank is for your money, because you need two or more banks for your key, while 1 bank for your money is sufficient. Correct?

I stay away from everything crypto but I don't see the difference. In both cases if they didn't make it right you'd go to the courts and make your case that they are at fault and owe you compensation.

In the first case, bank deposits are insured. In the second case, safe deposit boxes are not insured.

They're just different things. The FDIC insurance is for if the bank itself goes insolvent and they literally don't have enough money to cover their depositors' balances anymore. There's no reason a safe deposit box would be affected.

A fire, a flood, a robbery...

Is a bank deposit box not insured against those things? I've never really thought about it but always assumed they would be

Probably varies from bank to bank, but in my experience you have to specifically buy separate insurance if you want the content of your deposit box insured. The big problem from the bank's point of view is that, unlike your bank account, the bank doesn't know what you have in the box and thus has no idea what to insure it for and no way to verify any claim.

More importantly the bank doesn't profit more from something more valuable being in your safety deposit box so it doesn't make economic sense for them to be the one insuring it.

Yes, they are different things. A safe deposit box wouldn't be affected by the banks insolvency.

A safe deposit box may be affected by other things and if those things happen they don't have to "make it right", if you go to the courts and make your case you may find that they are not at fault and you are not owed any compensation.

The history of crypto says, "Good luck!"

There is a long history here of once trusted institutions turning out to be fraudulent.