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Author Topic: How do I generate a transaction offline (preferably with an offline website)?  (Read 76 times)
Nathan047
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January 02, 2018, 04:47:53 PM
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I generally use a Debian Live CD and an offline version of a web based wallet generator to create paper wallets for cold storage. When I go to spend from them I sweep them into a regular wallet and then send the funds I want to keep cold into a new cold wallet. However I was wondering if it would be possible for me to cut out some of the headache and just create the transaction on the offline computer and skip creating a new cold wallet. How would I do this?

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January 02, 2018, 06:18:33 PM
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I was wondering if it would be possible for me to cut out some of the headache and just create the transaction on the offline computer and skip creating a new cold wallet. How would I do this?
You can't create the transaction on an offline computer, it needs input from the blockchain to know your funds.

What you can do, is create the transaction online using https://coinb.in/#newTransaction . You'll only need your Bitcoin address for this, you don't need your private key.
Then, you can download the same website, and use it from your Debian Live CD to verify and sign the transaction offline.
The last step is to broadcast your transaction from your online computer.

This requires transfering an unsigned transaction to your offline computer, and after that a signed transaction to your online computer. An USB stick is easiest, or you can create and scan QR-codes if you're truely paranoid (like me).

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January 03, 2018, 03:43:44 PM
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That sounds like what I was looking for, thanks Loyce.

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January 03, 2018, 10:24:31 PM
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You can't create the transaction on an offline computer, it needs input from the blockchain to know your funds.

You must admit that it's fair only for web services. You can create transaction with core wallet in offline (it provides to you your utxo). Also, many online block explorers and some other services can provide to you such information. But without proper tools and some experience it will be hard task.

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January 04, 2018, 12:39:39 AM
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You must admit that it's fair only for web services. You can create transaction with core wallet in offline (it provides to you your utxo). Also, many online block explorers and some other services can provide to you such information. But without proper tools and some experience it will be hard task.
So, let's say I have an offline PC with Core that never connected to the internet. If I send 1 BTC to my address, how exactly can Core know the UTXO?

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January 04, 2018, 09:28:27 AM
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I was looking for something similar, where you sweep your paper wallets offline and once you go online again, the changes gets syncronized with the Blockchain. I have been playing around with offline transactions, but this is not what I need.

I want to reduce the amount of time that my paper wallet/private key is exposed online. It would even be better if the private key are encrypted, before you go online and decrypted before you syncronize the sweep action.

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January 04, 2018, 10:29:13 AM
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So, let's say I have an offline PC with Core that never connected to the internet. If I send 1 BTC to my address, how exactly can Core know the UTXO?

Without some "help" it won't.
But you can use blockchain.info for example.
See below:

At first you must know all unspent outputs for exact address. Then you are using any blockexplorer to get such information (txid)
Then you create raw transaction with createrawtransaction command. It has next arguments [{"txid":txid,"vout":n},...] {address:amount,...}
txid - is our txid
vout - the number of output (starts from "0")
address - is address of recipient.
amount - is amount of coins which you want to send (one important moment - difference between you output "balanace" and this amount will become fee for miners. So, if you have 1 btc and want to send 0.1 you also must show(means send to it) change address)
Then you must sign your raw transaction with signrawtransaction command and after that ( if status "complete" will be true ) you are able to send your transaction with online wallets (https://blockchain.info/pushtx for example)

To be honest, you can do that without Core wallet at all. There many special tools wich can help you to create transaction if you know only private key and txid of genesis transaction.

In science we trust!
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