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I have an offline wallet created by Bitcoin-QT. I want to send some of the bitcoins in this wallet to another address.

The most secure way I can think of is this:

  1. Boot from a Linux Live CD
  2. Install Bitcoin-qt and let Bitcoin-QT sync with the network
  3. Import the wallet to Bitcoin-QT and send bitcoins
  4. Save the wallet because of the change (https://en.bitcoin.it/wiki/Change) which was sent to a new created address in the wallet

But what happens if between step 3. and 4. your computer crashes? All bitcoins which should be left in your wallet are lost.

Is there a more secure way of sending bitcoins from your offline wallet with Bitcoin-QT? If not, whats the most secure way to do this in general?

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I don't think that is really a problem, but first of all why do you want to use a Linux Live boot? Is that to disable possibly installed malware? When you send your transaction make sure that you install your temporary bitcoin client on a persistent drive, e.g. not on the computers RAM (this will take a lot of time, so better clear out your computer instead of this approach). Your private key will be generated before you send your transaction, so you can't lose it when power shuts of.

This won't save you of course when power shuts down and your hard-drive crashes at the same moment, but when you are dealing with large amounts of bitcoins you could probably use some RAID configuration (e.g. RAID-1) for your hard-drives and still be fine. Or you could buy an external power source as backup.

  • Yes, I want to use a Linux Live CD because I am trusting it more to be maleware-free than my day-to-day system. – tymm Nov 21 '13 at 16:14
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You don't need to perform point 4 at all

All you need to do is generate and PRINT on paper your private key (Help > Debug window > Console > dumpprivkey your_wallet_address)

If you have private key you can restore later OFFLINE your current wallet.dat file on any PC or Mac computer

Here is how:

  1. Sync with the network without your wallet.dat

  2. Switch off internet connection and quit Bitcoin-qt

  3. Import wallet.dat with BTC on it

  4. If you don't have your wallet.dat file you can recreate it now: Run Bitcoin-qt and then click: Help > Debug window > Console > importprivkey your_wallet_private_key (it take a while because Bitcoin-qt must scan over 14 GB data (on my PC about half hour)) and then quit Bitcoin-qt

  5. Run Bitcoin-qt so your wallet will be updated

  6. Enter destination address and BTC value you want to send

  7. Switch on your internet connection and then click send button (so even if you have any malware or spy program on your computer it's impossible to steal your BTC because attacker have only few seconds when wallet.dat file with BTC on it is online)

NOTE: as a rule of thumb I always send all BTC from my current wallet.dat file and NEVER use it again

  1. Check on https://blockchain.info/address/your_wallet_address if your BTC was send and wait for 1 confirmation (if you give a tip it takes about 10 minutes, without tip about one hour)

  2. Switch off internet connection

You don't need to save your wallet.dat after step 9

You can restore later your current wallet.dat on ANY computer offline performing steps 1, 2 and 4 above)

Of course if you have a loot of BTC on ONE address it's smart move to split it on 10 different addressees

So even if something going wrong you lost only 10% of your BTC

Summary:

  1. Generate 10 (or 100) new BTC addressees on offline computer with Bitcoin-qt only (with fresh Windows, Linux or Mac OS install) - click: Receive and then 10 or 100 times click: +New Address

  2. Copy to TXT file all above addresses

  3. Generate and print for each BTC address private key (Help > Debug window > Console > dumpprivkey your_wallet_address)

  4. Delete wallet.dat file

  5. Restart or switch off your computer

Of course made 2 or more hard copy with printed private keys and store in 2 or more save places

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