Bitcoin Forum

Is it safe to re-use a paper wallet BTC address after spending it all? I spent it all in one transfer, so there was no "change" to be sent back to me. Does this make it safe to use this wallet again? I know for a fact that this private key is safe because I generated and printed it on an offline computer.

Does the mere fact of me having done a spend transfer with it on the blockchain make it less secure?

Why not generate a new paper wallet, just in case?

You will relate future transactions to previous transactions by reusing your public key. The effect is diminished anonymity, it's not really a security concern.

You had to import the private key somewhere to spend the Bitcoins from the paper wallet, so it's as secure as the place you've used it on.

this should be a technical answer as opposed to the o so common paranoia

Ah, that's a good point. Thanks


Yes, I'm looking for the technical reasons. I just want to fully understand how it works so I can truly make the best decision for myself.

Thanks for the answer. Yes, however I suppose it could be if the place where I used my private key ever got hacked or leaked it based on Birdy's answer.

Looks like it's generating new keys for me.

Well, re-using keys makes you vulnerable to flawed RNGs.

What are RNGs?

random number generators. see: the recent issue with android based wallets.

Flawed RNG == random number generator what returns only one number every time. Happened once in the history on a dumb hardware wallet.

When you don't reuse addresses, your bitcoins are protected by ECDSA (Elliptic Curve Digital Signature Algorithm), SHA-256 and RIPEMD-160. On a first transaction you publish your public key, so only ECDSA lefts. However, I believe that it is still pretty secure.

Notice that satoshi dice uses the same address over and over. As do many other block chain based games. Most vanity addresses are reused. Some mining pools reuse the same address for sending your mining income, directly or indirectly. Donation addresses are usually reused.

Congratulations for posting the only technical post.
ECDSA is indeed enough. If an EC becomes broken, Bitcoin won't be the first target.

Thank you for the explanation!

The fact that others make poor decisions isn't evidence that the decisions aren't poor.

While ECDSA is "enough" when used properly, there are issues that can arise that reduce your security when it is not used properly.

As an example, if the random number generator that is used to generate the k value when singing a transaction isn't sufficiently "random" it becomes possible for someone to use multiple signatures from the same private key to compute that private key and steal your bitcoins.  If you use a new address for each transaction, then you never have multiple signatures from the same private key, so this is no longer an issue.

Awesome. Another great technical reason. This is exactly what I need to hear. I feel like i actaully understand the benefits of not re-using a key now. Thank you everyone

Forgive the intrusion, but I'm curious, Danny. Do you really discard the private keys once you cleared the unspent output, as you state on your BTC trading post? Or do you keep them in archive wallets "just in case"?

It is safest to assume that I discard them regardless of what I actually do.  No harm at all can come from accepting that I discard them.