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Bitcoin rescue - 100$ reward. Copay multisig wallet. (self.Bitcoin)

bingbongboilredditor for 1 month が 投稿

Due to my misunderstanding how Copay works I have locked a small but significant amount of bitcoin in a multisig address which I cannot sign transactions for via Copay. I am happy to reward 100$ in btc to those who help me arrive at a solution.

I have the Trezor seeds underlying the 2-of-3 multisig addresses the coins are in. I only have the copay metadata associated with one copayer. I should have all the information necessary to retrieve the coins.

How I got here

I wanted to set up a 2of3 multisig cold storage wallet using Trezors for key management. I decided to use Copay because it had a similar security profile to Electrum and better UI. Unfortunately, Copays focus on simplicity limits its flexibility, and recovering funds from my multisig wallet deviates from the "normal user flow" in a way which is not supported.

A multisig wallet was created using Copay, and three Trezors from the Copay chrome app. I sent some test bitcoin to this wallet. I sent a test transaction from this wallet (which I later learned was not signed by my second Trezor and thus not broadcast). I then sent a small but significant amount of bitcoin to this wallet before realizing Copay was not allowing me to sign the transactions with a second key.

Copay observations

  • A payment proposal is an unsigned multisig transaction sent magically through the api to all copayers.
  • Each instance of a Copay multisig wallet is associated with one of the three keys (I'll call this the principal key).
  • Copay's UI only allows you to sign a payment proposal with the principal key of your wallet.
  • Restoring from a backup assigns the corresponding principal key to your copay instance. I only backed up one copayer's multisig metadata so I the UI only allows signing with that single principal key.
  • This was my misunderstanding, I thought this was just xpubs - not whatever Copay magic they use to make the multisig user friendly.

Possible avenues

  • I have started a payment proposal via Copay from one of the multisig copayers. Due to restrictions of the Copay interface I cannot sign for any other Copayers even though I have the Trezor corresponding to those xpubs. Option 1 is to figure out how to get Copay to let me sign with a second key.

  • I have imported the xpubs into Electrum and crafted the transaction to liberate my funds. I just need a way to sign it. For this avenue I think I need to: 1. convert my seed into the appropriate private key used to generate the multisig wallet; 2. Use those keys to sign the electrum transaction manually. Notably I only know the xpubs associated with the multisig wallet, and an approximate derivation path based on Copay documentation, not the exact key used.

The reward will be contingent on successfully broadcasting the valid transaction - I'm not sure how much beyond my private key I will need to know to appropriately sign this transaction and these things seem to surprise me. These keys will not be used again. Thanks for any help!

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[–]grnqrtr 1ポイント2ポイント  (8子コメント)

You could send me one of the seeds, I load it into my Trezor. You could then submit the payment proposal. I could go first, and then you could sign with the second key? Would that work?

Edit: This would only be good if you don't have any other bitcoin in the Trezor seed.

[–]bingbongboilredditor for 1 month[S] 1ポイント2ポイント  (7子コメント)

I would be happy to do this if it would work.

Unfortunately Copay doesn't allow one to sign payment proposals with arbitrary wallets. It's rather intuitive, and a bit hard to explain, but if the Copay instance hasn't "joined" the multisig wallet (using Copay magic) it cannot sign payment proposals - even if it is using the same seed/keys/address.

In addition I can only "join" the multisig wallet as one of the principal Trezors (due to the nature of my backups), so the UI is preventing me (or you) from signing as any additional seeds.

A workaround to this would be great!

[–]grnqrtr [スコア非表示]  (5子コメント)

Would any of the tools at coinb.in be helpful? I know you can create multisig wallets and create raw transactions. This one for example creates a multisig wallet.

Maybe you could use it to try to recreate the same multisig address that your coins are stuck in? I'm not sure, just a thought.

Edit: Yeah, I think you should try sticking your three xpubs in this coinb.in tool and then use the "redeem script" that it outputs in the New Transaction tab.

[–]bingbongboilredditor for 1 month[S] [スコア非表示]  (4子コメント)

I've actually crafted a transaction using Electrum spending the coins. Just need to sign it.

So in other words, starting from xpubs I can generate the appropriate addresses etc and make transactions. I just need a way to sign them.

[–]grnqrtr [スコア非表示]  (3子コメント)

I was testing creating them on coinb.in, I think you should try recreating it there. If you put the redeem script in the "new transaction" tab, it sets it up so that you can make and sign a transaction.

[–]bingbongboilredditor for 1 month[S] [スコア非表示]  (2子コメント)

I'll play with this tonight.

[–]grnqrtr [スコア非表示]  (0子コメント)

Yeah, you should. I made a random multisig with three xpubs then tried to make a transaction. It tells you the keys you need to sign with. I didn't finish the process because I was messing with an empty address, but I think it might work for you.

I'm going to bed. I hope you figure it out.

[–]Aardvaarkianredditor for 1 month [スコア非表示]  (0子コメント)

Currency of the future...

[–]grnqrtr 1ポイント2ポイント  (0子コメント)

Okay, I'm kind of understanding what the problem is ... I'll keep thinking.

[–]coiner2013 [スコア非表示]  (1子コメント)

"I only have a backup of the Copay metadata from a single copayer."

This should be your first sentence as it would prevent most people to read further.

[–]bingbongboilredditor for 1 month[S] [スコア非表示]  (0子コメント)

I have all the private keys which made the multisig address. The funds aren't lost, they are just obstructed by UI.

I need someone to help me manually sign a transaction, and navigate HD wallet key derivations. Not impossible, and possibly fun for the right person.

Edit: I added that info in the second paragraph, though, so its clear as you read.

[–]Aardvaarkianredditor for 1 month [スコア非表示]  (3子コメント)

Those multisig addies... Nothing but trouble :|

[–]bingbongboilredditor for 1 month[S] [スコア非表示]  (2子コメント)

You posed yesterday too! Is there an opinion behind the comments, or just poking fun at me. (deservedly)

I have never heard any negative arguments regarding multisig.

[–]Aardvaarkianredditor for 1 month [スコア非表示]  (1子コメント)

opinion behind the comments

Multisig addies add another layer of complexity, another opportunity to do it rong. If you (and you seem more savvy than most) and BFX can mess it up, what of Granny and uncle Jed?