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Let's say I have 10 bitcoins. I won't be using 8 of them any time soon. How can I put the 8 in a separate "offline" wallet not related to the bitcoin client?

This would be a good security measure. If the bitcoin client is ever compromised, only the remaining 2 bitcoins would be at risk.

It seems rather reckless to have all of one's savings in the same wallet.

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6 Answers 6

up vote 6 down vote accepted
  1. Go to your Bitcoin data directory
  2. Backup your wallet.dat to a safe location
  3. Move your wallet.dat away from the data directory
  4. Start Bitcoin. It will create new wallet.dat
  5. Get an address from the new wallet, save it in notepad
  6. Encrypt the wallet with some passphrase you will remember for a long time
  7. Turn Bitcoin off
  8. Go back to your Bitcoin data directory
  9. Take the new wallet.dat and store it somewhere safe
  10. Move your old wallet.dat file back into the data directory
  11. Run Bitcoin again.
  12. Send 8 Bitcoins to the address you saved in notepad

Now you have two wallet files - one with 2 bitcoins for your normal use, one with 8 bitcoins for keeping them safe. Just make sure not to lose either of the two wallets, or you'll lose your coins.

Keep your wallet.dats backed up and don't run duplicates at the same time.

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What happens if I run duplicates of the same wallet? For instance, if my mother accidentally spends 4 of those 8 backed up coins. Can I later take the original wallet file (of "8" coins), and spend the remaining 4? –  BitcoinButter Oct 24 '12 at 14:48
1  
@BitcoinButter Yes, you can, as long as your mother didn't spend those coins so many times the wallet had to use new addresses that were never part of the original wallet. Then only her wallet would be able to spend those coins. Copy of wallets drift apart after each use. This is why you shouldn't use the same wallet on more than 1 machine most of the time. –  ThePiachu Oct 24 '12 at 19:01
    
Does that hold for both sending and receiving address? –  BitcoinButter Oct 24 '12 at 19:48
1  
@BitcoinButter The most important information in the wallet are your keypairs. The public key is used for receiving bitcoins, the private one - for sending them. The wallet also stores information about all the transactions that took place on those keypairs, but that information can be retrieved from the block chain if needed. –  ThePiachu Oct 25 '12 at 5:04

I recently created a blog post about this: https://bitinnovate.com/creating-an-offline-bitcoin-wallet/

Steps for creating an offline bitcoin wallet

  1. Open the folder that contains your wallet.dat file
    • For Windows users: Go to Start -> Run (or press WinKey+R) and run this: %APPDATA%\Bitcoin
    • For Linux users: By default you Bitcoin should be here: ~/.bitcoin/
    • For Mac users: By default you Bitcoin should be here: ~/Library/Application Support/Bitcoin/
  2. Back up your wallet.dat file to a secure location
  3. Move your origional wallet.dat file out of this directory
  4. Start the Bitcoin client
  5. The Bitcoin client will automatically create a new wallet.dat file and a new address
  6. Copy the address and save it in notepad
  7. Encrypt the wallet with a secure passphrase
  8. Close the Bitcoin client
  9. Go back to the Bitcoin folder
  10. Move the new wallet.dat file out of this folder and store it somewhere safe. I suggest making multiple backups of this on multiple media types. I.e. CD, SD Card or a portable hard drive
  11. Move your old wallet.dat file back into the Bitcoin directory
  12. Run the Bitcoin client
  13. You can now send bitcoins to the address you copied down and they will be securely stored offline

To get the offline wallet back online. Move out the existing wallet.dat file and replace it with you offline file. Open the Bitcoin client and you will now have access to the bitcoins associated with that wallet.

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When linking to a post on another site it is generally a good idea to include some relevant part of that post in the answer, so that the answer is still useful even if the link does not work anymore. –  D.H. Nov 15 '12 at 21:06
  1. You better use off-line machine for generation secure bitcoin address. (see vanitygen)
  2. Thereafter send your money from on-line machine to this address.
  3. Bitcoin now are safe.
  4. Nobody know your private key.
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To save the copy/rename of your wallet.dat you could also use one of the alt-clients that have built in multiple wallet support. Both Armory and MultiBit show multiple wallets directly in the user interface.

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It seems there's a more secure and easier method. I'm a noob so please correct any mistakes, but I would suggest he create a paper wallet on bitaddress.org, print it off or memorize it or keep it on a USB flashdrive. Then he can go to his Bitcoin client, send 8 bitcoins to the public address of that newly-created private key and that will be most secure. Even if his client is hacked or PC crashes, those 8 bitcoins are damn secure.

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Founder of bitaddress.org steal your money like candy from a baby. –  user6203 Aug 5 '13 at 19:51

Step 1:

Step 2:

From Bitcoin.org client, send money, enter Bitcoin address, Qty 8 BTC. Press send.

Done.

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