"Multisig" for one person

[unknowncustomer]

Hello,

I expect to do cold storage through electrum with a 24 word seed.

I want to do « multi sig » but for only one person (me) instead of several people.
I expect to proceed like this:

1. Engrave recovery words 1-16 on the first metal device.

2. Engrave recovery words 1-8 and 17-24 on the second metal device.
3. Engrave recovery words 9-24 on the third metal device.

Hide the three plates in three different locations.
With 2 of them I can recover my funds.

Is it a good idea ? Can I improve this technique ?

[NotATether]

I don't see anything wrong with this technique other than that it becomes slightly more annoying to restore a lost wallet (you need to go to two different physical locations to collect all of the words).

Anyway, that's not true multisig since it's not cryptographically guaranteed to be so. Multisig refers to how transactions need at least X number of signers, and has nothing to  do with seed phrases. This is more like a redundant form of Shamir's Secret Sharing.

[hosseinimr93]

As mentioned above by NotATether, your wallet wouldn't be multi-signature.
If you want to have a multi-signature wallet, you need multiple seed phrases. For example, if you create a 2 of 3 multi-signature wallet, you will have 3 seed phrases and you will need 2 of them for signing your transactions.

[Zaguru12]

The technique will work out but personally I still think it defeats the purpose of multi sig since all the keys and seed phrase will be in your custody. If you are looking for security it would be better to use a single seed phrase and add a pass phrase to it for extra security. The single sig with passphrase is much easier to backup or save because you will have to save 3 things (key, seed phrase and passphrase) whereas for the 2 of 3 multi signature you will have Atleast 6 keys to save or backup (3 keys, 3 seed phrase). The transaction fee is also higher for 2 of 3 multi sig (it needs Atleast two different signers) than a single sig.

[odolvlobo]

I expect to do cold storage through electrum with a 24 word seed.

I want to do « multi sig » but for only one person (me) instead of several people.
I expect to proceed like this:

1. Engrave recovery words 1-16 on the first metal device.

2. Engrave recovery words 1-8 and 17-24 on the second metal device.
3. Engrave recovery words 9-24 on the third metal device.

Hide the three plates in three different locations.
With 2 of them I can recover my funds.

This technique is not recommended. The basic problem is that finding any one device reduces the the search space to only 8 words. Methods such as Shamir's Secret Sharing are better because you gain no information about the seed from any single device.

Watch this: Bitcoin Q&A: Why is Seed Splitting a Bad Idea?

[unknowncustomer]

The technique will work out but personally I still think it defeats the purpose of multi sig since all the keys and seed phrase will be in your custody. If you are looking for security it would be better to use a single seed phrase and add a pass phrase to it for extra security. The single sig with passphrase is much easier to backup or save because you will have to save 3 things (key, seed phrase and passphrase) whereas for the 2 of 3 multi signature you will have Atleast 6 keys to save or backup (3 keys, 3 seed phrase). The transaction fee is also higher for 2 of 3 multi sig (it needs Atleast two different signers) than a single sig.

Note that it will be on cold storage for long term.
If I have my seed phrase, could you confirm both key and passphrase are not compulsory to recover funds ?

[BlackHatCoiner]

Why don't you just setup a 1-of-3 multi-sig, and save three seed phrases along with their master public keys in the same, distinct places? That's the recommended manner to do what you want. Splitting a seed phrase in multiple places, or splitting one part twice, one of which can be merged with another that is also split similarly introduces complexity, which is the enemy of security.

[hosseinimr93]

If I have my seed phrase, could you confirm both key and passphrase are not compulsory to recover funds ?

If you add a passphrase to your seed phrase, you will need both seed phrase and passphrase to recover your wallet. If you lose either your seed phrase or your passphrase, you won't be able to recover your fund.
Note that if you extend your seed phrase with a passphrase, you will have completely different addresses.

[unknowncustomer]

If I have my seed phrase, could you confirm both key and passphrase are not compulsory to recover funds ?

If you add a passphrase to your seed phrase, you will need both seed phrase and passphrase to recover your wallet. If you lose either your seed phrase or your passphrase, you won't be able to recover your fund.
Note that if you extend your seed phrase with a passphrase, you will have completely different addresses.

Yes actually, I wanted to say password instead of passphrase

[hosseinimr93]

Yes actually, I wanted to say password instead of passphrase

Your addresses are derived from your seed phrase (+your passphrase, if there's any) and your password encrypts your wallet file locally.
If you lose your password and can't decrypt your wallet file, you can recover your wallet using your seed phrase (+your passphrase, if there's any).

[apogio]

Hello OP. I am sure you have established good knowledge here. But as a personal opinion, I want to tell you that I have done both:

1. 2-of-3 multisig. I mean actual multisig with 3 cosigners, where 2 are required.
2. cold storage (24 words seed phrase + passphrase).

In my humble opinion, for the average Bitcoiner, the option (2) is more than enough. It's good to understand how the option (1) works and give it a try, but option (2) is much much much simpler, both in terms of back-up and in terms of usage.

[unknowncustomer]

Yes actually, I wanted to say password instead of passphrase

Your addresses are derived from your seed phrase (+your passphrase, if there's any) and your password encrypts your wallet file locally.
If you lose your password and can't decrypt your wallet file, you can recover your wallet using your seed phrase (+your passphrase, if there's any).

By passphrase you mean 13th or 25th word right ?

Hello OP. I am sure you have established good knowledge here. But as a personal opinion, I want to tell you that I have done both:

1. 2-of-3 multisig. I mean actual multisig with 3 cosigners, where 2 are required.
2. cold storage (24 words seed phrase + passphrase).

In my humble opinion, for the average Bitcoiner, the option (2) is more than enough. It's good to understand how the option (1) works and give it a try, but option (2) is much much much simpler, both in terms of back-up and in terms of usage.

Yes but cold storage single sig I am afraid that someone finds my hidden location

[hosseinimr93]

By passphrase you mean 13th or 25th word right ?

Yes, passphrase is known as 13th or 25th word as well.
It may worth mentioning that your passphrase doesn't have to be a word. Passphrase can be any combination of words and characters.

[apogio]

Hello OP. I am sure you have established good knowledge here. But as a personal opinion, I want to tell you that I have done both:

1. 2-of-3 multisig. I mean actual multisig with 3 cosigners, where 2 are required.
2. cold storage (24 words seed phrase + passphrase).

In my humble opinion, for the average Bitcoiner, the option (2) is more than enough. It's good to understand how the option (1) works and give it a try, but option (2) is much much much simpler, both in terms of back-up and in terms of usage.

Yes but cold storage single sig I am afraid that someone finds my hidden location

Let's say you hide the 24 words on a piece of paper in a super secret place.

Let's say I find the piece of paper (because I am a super clever detective).

What can I do then? I will try to restore the wallet and I will see that it is empy. Why? Because you will have added a passphrase that ONLY YOU know.

So even if I stole your seed phrase, I would also need the passphrase.

P.S. The passphrase is a part of your wallet. It is not a password that is related to the application that you use. It is attached to your seed phrase, in order to create the seed for your wallet.