How to prove that a multi-sig-addresses (starting with 3) belongs to someone

[trapister]

For multi-sig-addresses (a subset of P2SH addresses) there are private keys, but there is no consistent definition on how a signature for a message would be verified. Thus, it's impossible to sign a message with an address starting with a 3 in a reliable way.
Therefore, I'm not able to prove via signing a message that a address starting with 3 belongs to me.
Even when I import the private key that Electrum give to me into another wallet, the address imported is different, starting with 1. Notice that I can sign message with this new address (starting with 1), but obviously the message is not linked to my original address starting with 3.
Please, anyone can help me??? Thanks a lot!!!

[ranochigo]

It is not possible for you to sign a P2SH address. P2SH works in a way such that a few public keys is needed to generate the address. The individual public keys are also valid Bitcoin addresses that starts with 1.

It is however, possible to sign a message with the addresses in the public key that is used to create the multisig. As long as you can get at least n signed messages in an n-of-m configuration, it is sufficient proof that you control the address.

[trapister]

It is not possible for you to sign a P2SH address. P2SH works in a way such that a few public keys is needed to generate the address. The individual public keys are also valid Bitcoin addresses that starts with 1.

It is however, possible to sign a message with the addresses in the public key that is used to create the multisig. As long as you can get at least n signed messages in an n-of-m configuration, it is sufficient proof that you control the address.

Thanks and sorry for my ignorance... please be in mind I'm a rookie...sorry!!!

I give you more information in case you can continues helping me:

My address starting with 3 is a Trustedcoin 2FA wallet generated by Electrum wallet. Therefore I'm not sure I've got the public key that was used to create the multisig. What I've got are the 3 publics keys and the private key correspondign to my address starting with 3.

I think is a 2-of-3 configuration (one of them is owned by Trustedcoin in order to make the 2FA process; and the other 2 it's supossed are mine) And the matter it's that I don't know how to get the 2 signed messages you told me to proof that I control my address starting with 3.

Please if you can be more detailed for me I'll be grateful!!!

[Muhammed Zakir]

It is not possible for you to sign a P2SH address. P2SH works in a way such that a few public keys is needed to generate the address. The individual public keys are also valid Bitcoin addresses that starts with 1.

It is however, possible to sign a message with the addresses in the public key that is used to create the multisig. As long as you can get at least n signed messages in an n-of-m configuration, it is sufficient proof that you control the address.

Thanks and sorry for my ignorance... please be in mind I'm a rookie...sorry!!!

I give you more information in case you can continues helping me:

My address starting with 3 is a Trustedcoin 2FA wallet generated by Electrum wallet. Therefore I'm not sure I've got the public key that was used to create the multisig. What I've got are the 3 publics keys and the private key correspondign to my address starting with 3.

I think is a 2-of-3 configuration (one of them is owned by Trustedcoin in order to make the 2FA process; and the other 2 it's supossed are mine) And the matter it's that I don't know how to get the 2 signed messages you told me to proof that I control my address starting with 3.

Please if you can be more detailed for me I'll be grateful!!!

Read https://www.reddit.com/r/Bitcoin/comments/3wyjev/comment/cy0275q. You will find there how to get master private keys and master public keys. You can generate address with it and sign a message. According to ranochigo, you need to sign message with an address created from each of the private keys.


@ranochigo: Even if he signs with address created from both of the keys, how can he use it to prove multisig address ownership other exposing your xpub key which I presume what you are thinking? Please enlighten me! Thanks! Nevermind. My ignorance!

[trapister]

thanks @ranochigo and @Muhammed Zakir
i'm closer to the solution
following your indications i've got the master private and master publics keys the multisig was created and now i've a multisig 2-3 (not a 2FA)
in order not to bother you, i'm trying to follow next step by myself...but i give up!!!
sorry to write you again... can you help me how can i do to follow your next indications???
thanks thanks

@ranochigo "sign a message with the addresses in the public key that is used to create the multisig. As long as you can get at least n signed messages in an n-of-m configuration, it is sufficient proof that you control the address"

@Muhammed Zakir "generate address with it and sign a message. According to ranochigo, you need to sign message with an address created from each of the private keys"

[HCP]

You can take a look at my guide for getting the addresses and keys that you need to sign messages from 2FA accounts here: https://bitcointalk.org/index.php?topic=1989369.msg19853098#msg19853098

Please do take note of the security warnings... exposing your xprvs should not done lightly and proper precautions should be taken.

[trapister]

thanks to all, folks!!!
at last i've got it.
the principal issue was i only get 1 of 3 private keys.
i've to got the private key from trustedcoin in order to get 2 of 3.
and at the end i've understand what all you wanted transmit to me.
thanks again for your support.

[Muhammed Zakir]

thanks to all, folks!!!
at last i've got it.
the principal issue was i only get 1 of 3 private keys.
i've to got the private key from trustedcoin in order to get 2 of 3.
and at the end i've understand what all you wanted transmit to me.
thanks again for your support.

AFAIK, Electrum 2FA creates a 2-of-3 multisig wallet with 1 in Trustedcoin's control and 2 in yours. If you have followed HCP's post, you should get two extended private keys(xprv) and you could generate address needed using them. So, did you do something wrong? Or did you really only got 1 extended private key(xprv)?