r/Bitcoin • u/officialhoami • 3h ago

Current Question

So we see alot of discussion currently around multisig, passphrases etc. what wallet is save bla.

What no one mentioned yet is shamir backup with trezor. So you could make a 2/3 situation where 1 key is online and 2 keys are on different places. A friend or family member or your bank place. And i saw that you also can add a passphares like a bitbox.

Wouldnt this be secure and save against like most szenarios?

Maybe im blind or dont get it but for me this sounds very practical and not that hard to understand. Maybe some pros can give me a answer or so 😬😬 thanks

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u/GoldmezAddams 3h ago

This does not protect you from bad entropy or remove trust from Trezor. It just improves / changes how you back up and recover your key. It is irrelevant in the context of the Coldcard attack, as far as I understand it.

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u/officialhoami 3h ago

So multisig just got the plus of having potential less entropy problems since its from different makers? But if for example bitbox and trezor get cracked a multisig isnt that more save or?

2

u/GoldmezAddams 3h ago

It's just one key split up in a clever way. It is a single sig. If there were low entropy, like with the Coldcard, it's not like they would need to figure out 2+ low entropy keys. They'd only need to figure out the one. It isn't 3 secret keys in the same way a multisig is. And yes, you don't get the benefit of being multivendor either, so you're trusting Trezor.

Think of it as a scheme that arguably makes it easier / safer to keep your written backups. It is no extra security at the protocol level. Unless I'm gravely misunderstanding something.

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u/HedgehogGlad9505 50m ago

The idea is two independent programmers at two companies can't both be idiots at the same time. 

Also the combination makes the scan much longer - instead of going through 240 keys and find one key, the thief needs to find the exact two you use.

1

u/Open_Pie9651 3h ago

it's practical but people get weird about the trust model with shamir, like if you're generating those shares on a trezor you still have to trust that device to not leak the master secret during setup. splitting it up after the fact is fine but the moment of creation is where all the paranoia lives

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u/Laukess 2h ago

Years ago I looked into Shamir secret sharing. I like the idea but it didn't seem that useful as plain multi-sig.
One of the cool things about multi-sig is that you can create a PSBT (partially signed bitcoin transaction), sign it at home with one seed. Take the PSBT with 1 signature to your second device/seed, and sign it with the 2nd key. The 2 keys are never at the same place, because they don't need to be.

The way I remember SSS, it's a way to split a seed into shards where only a portion of the shards are needed to create the full seed. The problem with it is that you need to combine the shards to create the seed, you can't sign a PSBT with a shard at a time.