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Author Topic: How to sign bitcoin transaction offline?  (Read 154 times)
allwelder
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March 18, 2019, 04:33:55 AM
Last edit: March 18, 2019, 06:19:04 AM by allwelder
 #1

With more hardware wallet coming,
How to sign transactions with bitcoin QT wallet offline, or how to send out bitcoin offline?

 
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The Bitcoin network protocol was designed to be extremely flexible. It can be used to create timed transactions, escrow transactions, multi-signature transactions, etc. The current features of the client only hint at what will be possible in the future.
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PrimeNumber7
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March 18, 2019, 04:48:40 AM
Merited by bill gator (2)
 #2

You will need to create a "watching" wallet within Bitcoin Core that is connected to the internet with your xpubkey, and create an unsigned transaction on the computer connected to the internet, and that has a copy of the up to date blockchain.

You will then need to transfer a copy of the unsigned transaction into Bitcoin Core (QT) from your online computer onto your offline computer, and use Core to sign the transaction. You then transfer the now-signed transaction back to your online computer, and can broadcast it via the command line.

I am not sure I understand how hardware wallets plays into, or is related to your question. AFAIK, hardware wallets are not compatible with QT and they are generally used in lieu of an offline computer. They could be used for the super-paranoid.

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March 18, 2019, 08:06:47 AM
 #3

I guess it is not what you are looking for but people may use something like physical bitcoins.  Something like this one: https://www.titanbtc.com/physical-bitcoins/
In this case you will get some physical thing with hidden private key on it.
Something like that already has been used in Venezuela when someone issued trade cards with pepe frog on it and you could literally pay with memes: https://dailycaller.com/2017/03/23/venezuelan-currency-slowly-getting-replaced-by-pepe-memes/
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March 18, 2019, 12:43:37 PM
 #4

With more hardware wallet coming,
How to sign transactions with bitcoin QT wallet offline, or how to send out bitcoin offline?

@PrimeNumber7 gave most of the details you need.
You don't send anything offline, you only sign offline. An online watch only wallet (or certain websites) will help you create the transaction.
You save that transaction, move it with a stick to the offline computer, sign it, go back to the online computer (or certain websites) and from there you can broadcast it.

More details about how to sign the transaction with Bitcoin QT wallet are here: https://bitcointalk.org/index.php?topic=651344.msg7306076#msg7306076



PS. Keeping an offline computer as cold storage is the safest way for storing Bitcoin. Safer than hardware wallets. Make sure that such a computer is indeed offline and remains offline forever.

allwelder
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March 18, 2019, 01:15:04 PM
 #5

With more hardware wallet coming,
How to sign transactions with bitcoin QT wallet offline, or how to send out bitcoin offline?

@PrimeNumber7 gave most of the details you need.
You don't send anything offline, you only sign offline. An online watch only wallet (or certain websites) will help you create the transaction.
You save that transaction, move it with a stick to the offline computer, sign it, go back to the online computer (or certain websites) and from there you can broadcast it.

More details about how to sign the transaction with Bitcoin QT wallet are here: https://bitcointalk.org/index.php?topic=651344.msg7306076#msg7306076



PS. Keeping an offline computer as cold storage is the safest way for storing Bitcoin. Safer than hardware wallets. Make sure that such a computer is indeed offline and remains offline forever.
Thanks for your explanation and link,that's exactly what I need.

 
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