<p>Excuse me, your question is not clear to me. You probably lack some basic knowledge about private/public keys, addresses and transactions in Bitcoin. I suggest you look up some material on how Bitcoin works: </p>

<ul>
<li>Quick explanation: <a href="https://bitcoin.org/en/how-it-works" rel="nofollow noreferrer">https://bitcoin.org/en/how-it-works</a></li>
<li>Bitcoin Wiki: <a href="https://en.bitcoin.it/wiki/Main_Page" rel="nofollow noreferrer">https://en.bitcoin.it/wiki/Main_Page</a></li>
<li>Detailed guides and references: <a href="https://bitcoin.org/en/developer-documentation" rel="nofollow noreferrer">https://bitcoin.org/en/developer-documentation</a></li>
</ul>

<p>NOTE: I would add this as a comment, but I don't have enough reputation to do so.</p>

CC BY-SA 3.0
2017-08-16T15:02:36.060Z
Ok got it. It was my mistake. I thought coins are stored in your computer with every bitcoin as its own address. Now I understand it perfectly.
Ajit Hegde
CC BY-SA 3.0
2017-08-16T14:40:13.677Z
2017-08-16T14:40:13.677Z
elias19r
<p>Every private key owner can spend any amount of coins on appropriate address, but every coin on any address can be spent only once. After spending the coin it is suggested to go into another address which has another private key.</p>

<p><strong>upd:</strong> Technically they are stored on the blockchain file (>200GB now), which of course is able to copy and wanted to be copied, but your private key is the only ability to let your coins be moved in the chain - if (and only if) you have the proper key. So, the proper key is hard to get and easy to lose and you might not like the idea to copy it except of backup operation.</p>

CC BY-SA 3.0
2017-08-16T14:19:48.247Z
2017-08-21T00:20:16.620Z
2017-08-21T00:20:16.620Z
Eimrine
<p>Your private key gives you access to your public key/address (wallet). Yes you can copy the private key as many times as you like (as people do for backing it up) but the same key is used for that same public key/address or any other address derived from that private key. An analogy would be making multiple copies of you front door key. You will have multiple keys but they still only open one door.</p>

CC BY-SA 3.0
2017-08-16T14:21:40.657Z
2017-08-16T14:21:40.657Z
Josh
<p>I am very new to bitcoins. I have one question. Suppose some one copied their private key and saved it in their harddisk. Next they will do the transaction. Now since you already copied the private keys can you use it again?</p>

<p>How bitcoin prevent this?</p>

<p>I am asking this because. I wish to create something smaller for my brothers  school project. So I am out of ideas on how to prevent this.</p>

<transactions><blockchain><bitcoin-core><bitcoind><private-key>
What happens if you copied private key and try to use it again?
Ajit Hegde
# What happens if you copied private key and try to use it again?

(Asked by: username_0 on 2017-08-16)

I am very new to bitcoins. I have one question. Suppose some one copied their private key and saved it in their harddisk. Next they will do the transaction. Now since you already copied the private keys can you use it again?

How bitcoin prevent this?

I am asking this because. I wish to create something smaller for my brothers school project. So I am out of ideas on how to prevent this.

**Tags:** transactions, blockchain, bitcoin-core, bitcoind, private-key


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## 3 answers

### Answer by username_1 on 2017-08-16. Score: 0 | Accepted answer

Excuse me, your question is not clear to me. You probably lack some basic knowledge about private/public keys, addresses and transactions in Bitcoin. I suggest you look up some material on how Bitcoin works:

* Quick explanation: <https://bitcoin.org/en/how-it-works>
* Bitcoin Wiki: <https://en.bitcoin.it/wiki/Main_Page>
* Detailed guides and references: <https://bitcoin.org/en/developer-documentation>

NOTE: I would add this as a comment, but I don't have enough reputation to do so.

> **Comments:**
> **username_0**: Ok got it. It was my mistake. I thought coins are stored in your computer with every bitcoin as its own address. Now I understand it perfectly.  

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### Answer by username_2 on 2017-08-16. Score: 0

Every private key owner can spend any amount of coins on appropriate address, but every coin on any address can be spent only once. After spending the coin it is suggested to go into another address which has another private key.

**upd:** Technically they are stored on the blockchain file (>200GB now), which of course is able to copy and wanted to be copied, but your private key is the only ability to let your coins be moved in the chain - if (and only if) you have the proper key. So, the proper key is hard to get and easy to lose and you might not like the idea to copy it except of backup operation.


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### Answer by username_3 on 2017-08-16. Score: 0

Your private key gives you access to your public key/address (wallet). Yes you can copy the private key as many times as you like (as people do for backing it up) but the same key is used for that same public key/address or any other address derived from that private key. An analogy would be making multiple copies of you front door key. You will have multiple keys but they still only open one door.


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