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Author Topic: Paper wallet - spending a little - what is the risk?  (Read 963 times)
MNDan
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January 29, 2014, 06:29:14 PM
 #1

Hi all - I have a paper wallet with a bunch of bitcoin, and I just want to send a little to my online blockchain wallet.

If I do this, and correct me if I am wrong, blockchain just sends the "change" back to my original paper wallet. Everyone says you shouldn't do this, but I don't really understand the risk. Everyone can see the public key of my paper wallet the second I load it, so why is there a risk in sending the change back to the same paper wallet and having my public key made public twice?

thanks!
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January 29, 2014, 06:32:05 PM
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The address isn't exactly the public key: it's a double hash of the public key AIUI. The public key is revealed only when funds are spent from an address. For absolute maximum security, it's best not to reuse a paper wallet. However, this becomes totally critical when the change is sent to a third address (e.g. by bitcoind or Bitcoin-Qt) because it is not wholly unheard of for unwary users to have made the grave mistake of deleting the live wallet due to falsely believing the change has been returned to the paper wallet, thus losing a lot of money.

"Do not reuse cold wallet addresses" is basically sound advice, especially when you can easily create fresh ones.

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MNDan
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January 29, 2014, 08:27:46 PM
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Thanks! Great response.
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January 29, 2014, 11:07:55 PM
Last edit: January 30, 2014, 12:01:56 AM by odolvlobo
 #4

Hi all - I have a paper wallet with a bunch of bitcoin, and I just want to send a little to my online blockchain wallet.
If I do this, and correct me if I am wrong, blockchain just sends the "change" back to my original paper wallet. Everyone says you shouldn't do this, but I don't really understand the risk. Everyone can see the public key of my paper wallet the second I load it, so why is there a risk in sending the change back to the same paper wallet and having my public key made public twice?

You cannot send bitcoins using a paper wallet because it simply doesn't have the ability. In order to spend the bitcoins in a paper wallet, you must import the private key into a wallet that can send bitcoins.

Once you import the private key, you should destroy the paper wallet or at least store it very securely because anyone that sees it can still spend your bitcoins. Also, you shouldn't reuse the paper wallet because the key is now in another wallet and that might cause confusion.

Blockchain.info has a feature where you can "sweep" the private key. All that does is sends the bitcoins from the paper wallet's address to a new address in the blockchain.info wallet. In this case the paper wallet is no longer useful because it no longer contains any bitcoins, but there is no reason why you can't reuse it.

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January 31, 2014, 07:52:29 AM
 #5

for example theres still a risk to be ripped off irl
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January 31, 2014, 12:43:18 PM
 #6

When you send bitcoin out of an address, the public key (not to confuse with private key) will be known to the world.
That's why, bitcoin-qt will always generate a new change address for your every transaction.
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