After a multisig address is created, can one of the private keys of that address be known by an unrelated person and the security of that address still remain uncompromised?

My understanding being that nobody would be able to spend from that address without the other signatures

  • What do you mean by "the" private key of a multisig address? The whole point is that there is more than one private key. Jul 22, 2014 at 15:08
  • @NateEldredge I had imagined that other existing addresses were used to make a single multisignature address.
    – CQM
    Jul 22, 2014 at 15:38
  • I think I can guess what you are asking. I'll post an answer. Jul 22, 2014 at 15:48

2 Answers 2


I think your question may stem from a misconception.

An ordinary Bitcoin address is the hash of a public key (plus a few extra bytes), which in turn is associated to a private key. So in that sense an ordinary address has a private key.

Multisig addresses do not work like that. The address is not the hash of a public key, and so there is no private key directly associated to the address. Rather, a multisig address is the hash of a script. The script in turn lists the public keys whose signatures will be needed to redeem the transaction. I think it is these keys that you are referring to as "existing addresses" in your comment.

So spending the transactions requires you to know the private keys of the intended recipients. There is no other private key involved.

Also, there is no real problem if other people know the script whose hash is the multisig address. The only extra information it contains is the public keys of the recipients. This might help someone identify who those recipients are (though the script has to be revealed in order to spend the transaction, so this information will eventually be public anyway), but it doesn't help them spend it.

For more information, see these answers:

How will multisig addresses work?

What is "Script Hash" address exactly and how does it work?

  • @Nate Eldredge good answer, except you say "...spending the transaction requires you to know the private keys of the intended recipients." I think you meant to say something like "spending the transaction requires you to know the private keys of the addresses used to form the multisig address. If you knew the private keys of the intended recipients you would steal their bitcoins by transfering theose addresses' contents to your own wallet. I have a question of my own: How is the hash of the script the multisig address? You say this in the final large paragraph.
    – almel
    Jul 22, 2014 at 18:24
  • @almel: I maybe shouldn't have said you. Spending the transaction requires signatures from all the private keys corresponding to the public keys listed in the script. It's not actually necessary that a single person know all the private keys, but if you, an attacker, wanted to spend it without anyone else's cooperation, you would need all those private keys. (Depending on whether they have been used before, those private keys might also allow you to spend other, possibly single-signature transactions and steal some coins.) Jul 22, 2014 at 18:36
  • @almel: The details of how to form a multisig address as the hash of a script are discussed briefly in the second answer I linked, and it has a link to BIP 16 which is the authoritative reference. Jul 22, 2014 at 18:38

Yes if only one private key has been compromised but the multisig address requires more than one co-signer sign transactions then the funds can't be stolen. You can have between 1 and 15 co-signers for a multisig address and require 1 or more of them to approve spending transactions by signing them. If you only require 1 and any one of the co-signers' private keys has been compromised then the funds can be stolen. If however you require more than one signature then obviously the theft of one private key is not enough to steal the funds.

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