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Assume you have the following situation: You are going to create a new multisig wallet with Electrum. 2 signatures are from old hardware wallets and 1 signature is brand new.

The new multisig will only be used with Electrum and Electrum personal server connected to Bitcoin Core. The 2 old signatures from the hardware wallets has been used with the hardware wallets own wallets (like Ledger Live and Trezor Wallet). Then I guess we can assume that the master public keys from those 2 wallets has been uploaded to some server somewhere and could be "leaked".

From a privacy standpoint, if I create a new multisig, is it possible to get any information from the 2 old master public keys? Or, do you need all 3 keys?

Would it be a good practice to create two new master public keys (by "reinstalling" the old hardware wallets) and create a new multisig with 3 brand new keys (and treat them with more care in the future)? Or is it fine, because 1 key is new?

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From a security perspective related to spending bitcoins, since only the master public keys have been compromised, there is no way that the attackers can derive the child public keys as they do not have access to the chain code. However, if the chain code is also revealed, there is no way to derive child private keys and hence the attacker cannot spend the funds. So if you are trying to create transactions with 1-of-3 or 2-of-3 multi-sig, the attacker still does not have access to the signatures (since he does not have the private keys)

However, if you are going to create a P2SH address of all the 3 public keys involved, there is no way anyone can recreate this address even if they know the 2 of the 3 public keys.

  • Thanks for the reply! I was more concerned from a privacy standpoint (and not security). If it's possible to know all addresses (and the full balance of the wallet) from only 1 master public key in a multi-sig. But I guess it's not possible then. And if you want to generate a fresh master public key, you could simply create a new passphrase for your seed. So, not that much trouble to go through, – Helge Hundingsbane Mar 2 at 15:46
  • The way that wallet balance is calculated is by scanning the blockchain from the hash of all 3 addresses (I assume that you will create a P2SH instead of using the raw public keys as script). Since one of your master public key will always be private, the malicious actor would never be able to calculate the has effectively as all the 3 public keys will be used to create one. – Ugam Kamat Mar 2 at 15:52

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