Improving multisig setup

[unknowncustomer]

Hello,
I created an offline 2/3 multisig wallet on electrum.
The 3 keys are geographically distributed, however 2 of them are very closely located.
I would like to improve this setup by duplicating one of the private key and either:
- Store it in a 4th location
- Store it offline on my iPhone ? Is it possible ? Encrypt it on my computer ?
Any thoughts ?

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[Charles-Tim]

- Store it offline on my iPhone ? Is it possible ? Encrypt it on my computer ?
Any thoughts ?

No need of doing something like this. You can backup your 2-of-3 multisig seed phrase/private key and public key in this order in three different locations:

Seed 1, MPK 2 (location 1)
Seed 2, MPK 3 (location 2)
Seed 3, MPK 1 (location 3)

In this way, if you lose one backup, you will still be able to recover back your coins and there is no need for any fourth backup, especially in what is not recommended like phone or online.

Backup should be completely  offline.

[Stalker22]

~
Any thoughts ?

All private keys should be stored entirely offline. What is the point of geographically distributing keys if they are kept online? The Internet does not respect borders or geographical distances.

Store it offline on my iPhone? Your iPhone is not an offline device. It is safer to use hardware wallets or dedicated offline storage devices.

[Zaguru12]

Is it possible ? Encrypt it on my computer ?

Encrypting your wallet or file in which you store something only secures it from been physically accessed but when an internal attack like malware comes in then they would get access to it even with the encryption on it.

You don’t need the fourth location just follow the instructions above by Charles-Tim and make sure it is a three different location although the third location can be far from you since you don’t really need the third key to sign your transactions since it is a 2-3 multi sig. storing them in numerous places get it affected in terms of redundancy.

[hosseinimr93]

If I understood you correctly, you worry about losing both of the keys that are located close to each other at the same time and that's why you want to have one of them in another location as well.

You can even have two copies of each of the keys and keep them in six different locations. In this way, you can decrease the chance of losing access to your wallet, but you should take note that you increase the chance of someone gaining access to your wallet.

You said you have two of keys in close locations. If it's possible that someone can gain access to both of them at the same time, you are defeating the purpose of a multi-signature wallet.

[Z-tight]

I would like to improve this setup by duplicating one of the private key and either:
- Store it in a 4th location

If the changes you want to make is because two of your backups are in close proximity, then why do you want to add one more backup and store it in a different location, when you can separate the backups in close proximity by moving one of them to this location you have in mind. Take note that too many backups can be complicating and if you are not at risk of a physical or a local attack, two of your backups can be in close proximity, but just not on the same device.

- Store it offline on my iPhone ? Is it possible ? Encrypt it on my computer ?
Any thoughts ?

This is not a good option, except the device is airgapped, if it is online it is not recommended even if it is encrypted.

[BitMaxz]

It's too risky if you have multiple copies of your backup keys that's not the best security practice.

If you want to keep them safe the first thing you should do is to generate them from an offline device and transfer them offline to where you want to save them just make sure the place where you want to store them is totally offline and securely safe even they are close or nearly located.

Why not mention here the 2 locations? So that we know how far the 2nd backup key and let's see if it's a secured place.
If you mean storing it on two different iPhones then that's not a good place to store keys because it's an online device unless you decide to never connect it to the internet.

[Bitcoin Smith]

- Store it offline on my iPhone ? Is it possible ? Encrypt it on my computer ?
Any thoughts ?

Smartphones are not suitable because its likely to be connected to internet at some point. Storing it any form digital form pose the risk.

As others said you should keep the seeds in offline format which can be on a piece of paper inside water and fireproof box or you can look for the secret ways like this one Securing Your Seed Phrase with Washers.

Duplicating a single key doesn't make sense because it would only result in having the same key in two locations. The best practice is to store the three keys at three separate locations where one has no connection or association with the others and is positioned far from the remaining two.