Best way to split up a balance from cold storage? (bitcoin core)

[sam49w]

Hey,

I have a single private key in cold storage with about 10 coins in it. This is a lot to me. The address was generated offline a while ago in using a computer that never touched the internet.

I want to break the balance up into smaller amounts that I am more comfortable with. I would like to break it up into multiple addresses.. ie 2 or 3 coins in each. I could then import them individually if I ever wanted to spend them.

How can I do this without importing my current private key into to a "live" computer connected to the internet? That is to say, even if I build a new Linux computer, install core, import the key, create a transaction (internet disconnected)... connect to the internet to allow it to broadcast - if my opsec is broken somewhere - some rogue software could still create an alternative transaction and broadcast that instead.

I would really like to use Bitcoin core offline somehow. I thought about installing the latest version of core on an offline machine, create a transaction... and export the tx hash. However, the offline machine would need a copy of the blockchain.. and the "bootstrap.dat" option is no longer available.

How can this be done safely?

Thanks

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[findftp]

Armory wallet can do offline import and offline transactions.
Take a look at it.

[shorena]

You can make a TX entirely offline and have the network confirm it at the same time. You can however create an unsigned TX, sign it on your offline machine, transfer it to any online computer and broadcast to the network. That way the private key was never online. Bitcoin core allows you to create raw unsigned TX via the console with createrawtransaction. Enter help createrawtransaction for an example. All you need is the TX ID of the TX that send the 10 BTC to an address and the 5 (or 10 or 20 or...) new addresses. Read the safety advice by Danny below!

Keep in mind that you dont manually set the fee when creating a raw transaction. The fee is what is left. E.g. if you send 10 BTC to 10 addresses let them receive 0.9999 each for a (10-(10+0.9999)=) 0.001 BTC fee.

[DannyHamilton]

Be very careful about using createrawtransaction if you are not absolutely sure that you know what you are doing and that you haven't made any mistakes.  People have been known to make errors using it that have ended up losing them nearly all of their bitcoins.

One of the more common mistakes people make is to forget that they MUST send the change from the transaction to an output that they control.  The createrawtransaction will not do this for you.  If you forget to do that, then ALL of the change from the transaction becomes transaction fees.

Other common errors are typos when setting the output values.

You may want to use a wallet that is designed to help you do this sort of thing, such as the Armory that findftp mentioned.

[sam49w]

I don't want to attempt creating a raw transaction.

I thought I could simply use the Bitcoin core GUI, and then dump the signed tx ... and broadcast if from another PC. However, the offline machine would need a copy of the blockchain.. and the "bootstrap.dat" option is no longer available.

How do others safely spend large amounts of bitcoins? I know of Armory, but I could prefer to use Core which has many developers and a lot of support.

[DannyHamilton]

How do others safely spend large amounts of bitcoins? I know of Armory, but I could prefer to use Core

I'm not certain, but my impression has always been that those that want to manage large amounts of bitcoins offline typically use Armory.  That's what I would use if I was going to try to access a significant amount of bitcoins from a paper wallet.

I thought I could simply use the Bitcoin core GUI, and then dump the signed tx ... and broadcast if from another PC. However, the offline machine would need a copy of the blockchain.. and the "bootstrap.dat" option is no longer available.

Hmm.  I suppose you could install Core on an online computer and allow it to get fully synchronized.  Then you could copy the bitcoin folder onto a removable hard drive and install that on the offline computer.  You'd then be able to create the transaction (or transactions) with the GUI.  You could extract those transactions from the offline computer and use sendrawtransaction on the online computer to broadcast them.

Keep in mind that if you don't use coin-control the Core wallet will generate RANDOM addresses and send the change from the transactions to those RANDOM addresses.  As such, you will no longer have any bitcoins in your original paper wallets.  You'll want to make sure you either use coin-control or send ALL the bitcoins to new paper wallets.

[bitbaby]

Danny already explained how to do it with Core, though you can do it more easily and safely with electrum.

Create a watch only wallet, import your public key, create a raw transaction, take it to the offline machine, sign it, bring it back to the watch only wallet and broadcast it from there, your private key remains offline so no one can make any transactions other than the one you created.

Make sure to create 2-3 paper wallet prior to this safely and split that balance to them and for more security don't use the paper wallet you had before again.

[calkob]

This seems really hard for a newbie to work out any chance of a more detailed breakdown?  or should noobs just stay clear?