Thanks for the clarification. This confirms my assumptions.
Not a summary, but my own opinion: partially leaked seeds are vulnerable for brute forcing at some point in time. Shamir's secret sharing can be used instead.
That's a good question. A difference is that with 1-of-2 you don't need to deal with partially signed transactions, which might be a convenience with less experienced bitcoiners (like my heirs).

@LoyceV
Thank you for your answers.

RE Q1:
I understand the public key will be available on the blockchain if transactions are already done, but how does the attacker know which transaction? The public key of a seed differs if it's part of a multi sig wallet or a single sig wallet right?
RE Q2:
Safer from an attacker
RE Q4: That's also an option, but passphrases can be forgotten. I'm not saying this setup is a good idea, I just want to know the details and make a good decision.

@alexeyneu
I'll read that stack exchange page. Thanks.

@hosseinimr93
This is for a wallet with less funds and I want it to be able to manage it with max 2 wallets.

@apogio
Thanks for the link.

@alexeyneu
It's not a given attackers know how much you have.

@nc50lc
"A client/wallet will not be able to sign by having only the private key of a single signer without the redeem script or cosigner's public key to reproduce it."
Clear! It's essential to store the public key of each cosigner. If they are not leaked, the private key can't move funds.

Sorry, it's not 100% clear for me. If that other guy doesn't have both public keys, can he still transfer the funds?
Sorry, it's not clear yet for me. I'm trying to ask questions which could be answered with yes or no, but your answer is confusing me. Without both public keys, it's not possible to move funds (question 1)?

I understand, if you have both public keys and have one private key, you can move the funds, but that's not what my confusion is about.

You can move funds without knowing both public keys and with only one private key (seed)?

When I create a multi sig wallet with Electrum, it's showing the following warning:
"Warning: to be able to restore a multisig wallet, you should include the master public key for each cosigner in all of your backups."
This suggest you cannot send funds with ONLY one private key (seed). Am I reading this wrong?

Suppose I have a 1 out of 2 multi sig setup, which seed A in location A, seed B in location B and the public keys stored in location C.
question 1: If seed A is leaked, is it true the attacker still can't access the funds because he doesn't know the public key related to seed B?

question 2: Would this setup be safer compared to having one seed into two places?

question 3: Can the attacker extract info if the seed is part of a multi sig setup?

question 4: With the 1 out of 2 multi sig setup, can I put some small funds on addresses related to the seed in single sig setup, so the attacker would think he got bait, but in fact he only gained access to the small funds and not the full fund?

@Cricktor I didn't follow a tutorial exactly, but I've read https://electrum.readthedocs.io/en/latest/multisig.html and https://bitcoinelectrum.com/creating-a-multisig-wallet and of course I made a mistake. I didn't consider the consequences of the "Enter cosigner seed" option.

Thank you for the reminder. I'll store the seeds in different locations and all public keys in multiple places.

@nc50lc
That's exactly what I mean. I'm glad I checked this (and asked about the confusion) before doing any valuable transactions.

That's true, and I think it would be a nice addition to the information dialog to show for which cosigners the current wallet can also sign the transaction.

Wonderful! Thank you all so much, especially nc50lc.

Wallet C (actually it was the first one that I created) contained all 3 seeds, I didn't know that was possible.
I assumed when creating a wallet and you insert the 3 seeds, it would store the first seed and compute the public key of the other two and store them.
It's confusing the UI is showing the "main said" and not the others.

@BitMaxz

If wallet C thinks that's a unsigned transaction, although it's a signed transaction, that would mean wallet W could sign transactions, but that would be wrong because it's a view-only wallet. I even re-created the view-only wallet just to be sure it would use only public keys.

I don't think there are any mistakes made during creation if all addresses across all four wallets are the same right?

Not sure yet where my mistake is. 

The wallets are all created with 4.5.3 and yesterday I updated to 4.5.4, but no effect.

@Z-tight

Thank you for your response.

Let me clarify.
1. I signed the unsigned transaction with wallet A and it said partially signed. I didn't save the partially signed transaction.
2. I repeated this for wallet B, so I signed the unsigned transaction again (so not the partially signed transaction of wallet A, because that one I did not save.) and it said again that is was partially signed. Again, I didn't save the partially signed transaction.
3. I repeated it again for wallet C. I signed the unsigned transaction and it said (full) signed! It was not necessary to sign it with another wallet in order to broadcast it.

I thought, this is not possible, but I repeated this process 2 times again to verify.

Hope it's clear now.

Hi,

I'm playing around with a multi-sig wallet and I've the following setup.

• PC with a view-only wallet W with internet.
• Old laptop with 3 wallets (A, B & C) with seed and without internet
• They a list the same addresses

When I create a transaction (with just 10sats/vbyte to confirm it gets into the mempool, but it's not executed anytime soon if at all) from wallet W it's unsigned. I store the transaction on a usb stick and copy it to the laptop. When I load it in wallet A and sign it, it says partially signed. The same holds for wallet B.

When I do the same for wallet C (based on the same unsigned transaction), it says it's (fully) signed. I can even copy the (signed) transaction to the PC and broadcast it from there. I verified it twice and I'm sure I didn't import a transaction that was already partially signed by wallet A or B.

How is it possible that a 2 out of 3 setup only needs one signature? Please let me know if you need more details.

What error did you get?

What is the difference between trading in this topic (or a separate topic) and your forum?

So, what are the future plans?

Logo 2 for sure. Good job Probeer.

9JVrFcLVhjjxMxa7EgBUTPH5Ta3kEemSM1

It works like a charm. No troubles with compiling / running / (pool) mining.

After compiling on Ubuntu I received the following error on command ./frozen-qt:
"Error loading wallet.dat: Wallet corrupted"
Same problem after rm ./frozen/wallet.dat.
Any help?

Follow these instructions http://worldcoinforum.org/topic/21-how-to-compile-wdc-wallet-in-linux/
and remove ~/.worldcoin/peers.dat before starting ./worldcoin-qt for the first time.

Received the first half of the payment before sending the coupon code and received the other half afterwards. Everything went well.

Bump.