<p>Reusing an address is a security issue if you have a weak random number generator, as was an issue with the Android Bitcoin Wallet. I should note this was android's fault for using a bad generator and was fixed quickly by the app developer, though some people lost coins because they had signed multiple messages (i.e. transactions) with the same address and the number generator used the same random number for more than one transaction, for more info you can see this: <a href="http://gigaom.com/2013/08/12/why-bitcoin-users-using-android-wallet-apps-need-to-upgrade/" rel="nofollow">http://gigaom.com/2013/08/12/why-bitcoin-users-using-android-wallet-apps-need-to-upgrade/</a></p>

<p>If you'd like to know more about why using the same random number in two messages is bad, you can read about ECDSA (ecliptic curve digital signature algorithm) here: <a href="https://en.bitcoin.it/wiki/Protocol_specification#Signatures" rel="nofollow">https://en.bitcoin.it/wiki/Protocol_specification#Signatures</a></p>

<p>Also if you are concerned with the people you transfer bitcoins with knowing how much money you have and when you're sending money, and possibly to whom, you should consider keeping your addresses and transactions separate. This involves choosing which inputs you use to send transactions, using a system like armory allows you to do this.</p>

CC BY-SA 3.0
2014-02-19T13:01:24.477Z
Do you have a source for "some people lost coins" because of the android rng bug?
Jannes
CC BY-SA 3.0
2014-03-11T05:20:06.923Z
I agree with James that it would be nice to have a source on "some people lost coins". Even with that, though, it sounds like only the people who reused an address lost coins, not even other users of the same buggy pRNG.
Daniel H
CC BY-SA 3.0
2014-07-13T18:56:53.000Z
You can look through this thread here, it talks a lot about the issue with the Android Bitcoin Wallet https://bitcointalk.org/index.php?topic=271486.0/ . About 55 bitcoins were stolen , and it is verifiable since they come from addresses that were compromised due to bad signatures.
k kurokawa
CC BY-SA 3.0
2014-02-19T10:28:56.157Z
2014-02-19T10:28:56.157Z
Mark
<p>There is already <a href="https://bitcoin.stackexchange.com/q/20621/1725" title="Is it safe to reuse a Bitcoin address?">a question</a> that ask why you shouldn't reuse addresses, but it's about whether or not it's a bad idea for the person who would do the reusing. I understand there are several reasons you'd want to avoid reusing (e.g., fear that ECDSA isn't secure, privacy and anonymity concerns, difficulty of tracking senders, etc.); as far as I can tell, it's still sometimes worth it on an individual level to reuse an address.</p>

<p>However, the Bitcoin Wiki says in multiple places (<a href="https://en.bitcoin.it/wiki/Firstbits#Contradicts_design_of_Bitcoin" rel="nofollow noreferrer" title="One argument against Firstbits and vanity addresses">here</a> and <a href="https://en.bitcoin.it/wiki/FAQ#Why_does_my_Bitcoin_address_keep_changing.3F" rel="nofollow noreferrer" title="Why the default client changes your receiving address">here</a>) that reusing an address degrades the security of the whole network; I also think I've seen this claim elsewhere but can't track down the source anymore. I don't understand how this could degrade the security of the network, and if it does, what's to prevent an attacker from repeatedly doing this before an attack if it would help?</p>

<security><vanity-address><address-reuse><firstbits>
Does it hurt the network to reuse addresses?
Daniel H
# Does it hurt the network to reuse addresses?

(Asked by: username_0 on 2014-02-19)

There is already [a question](https://bitcoin.stackexchange.com/q/20621/1725 "Is it safe to reuse a Bitcoin address?") that ask why you shouldn't reuse addresses, but it's about whether or not it's a bad idea for the person who would do the reusing. I understand there are several reasons you'd want to avoid reusing (e.g., fear that ECDSA isn't secure, privacy and anonymity concerns, difficulty of tracking senders, etc.); as far as I can tell, it's still sometimes worth it on an individual level to reuse an address.

However, the Bitcoin Wiki says in multiple places ([here](https://en.bitcoin.it/wiki/Firstbits#Contradicts_design_of_Bitcoin "One argument against Firstbits and vanity addresses") and [here](https://en.bitcoin.it/wiki/FAQ#Why_does_my_Bitcoin_address_keep_changing.3F "Why the default client changes your receiving address")) that reusing an address degrades the security of the whole network; I also think I've seen this claim elsewhere but can't track down the source anymore. I don't understand how this could degrade the security of the network, and if it does, what's to prevent an attacker from repeatedly doing this before an attack if it would help?

**Tags:** security, vanity-address, address-reuse, firstbits


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## 1 answers

### Answer by username_1 on 2014-02-19. Score: 2

Reusing an address is a security issue if you have a weak random number generator, as was an issue with the Android Bitcoin Wallet. I should note this was android's fault for using a bad generator and was fixed quickly by the app developer, though some people lost coins because they had signed multiple messages (i.e. transactions) with the same address and the number generator used the same random number for more than one transaction, for more info you can see this: <http://gigaom.com/2013/08/12/why-bitcoin-users-using-android-wallet-apps-need-to-upgrade/>

If you'd like to know more about why using the same random number in two messages is bad, you can read about ECDSA (ecliptic curve digital signature algorithm) here: <https://en.bitcoin.it/wiki/Protocol_specification#Signatures>

Also if you are concerned with the people you transfer bitcoins with knowing how much money you have and when you're sending money, and possibly to whom, you should consider keeping your addresses and transactions separate. This involves choosing which inputs you use to send transactions, using a system like armory allows you to do this.

> **Comments:**
> **username_2**: Do you have a source for "some people lost coins" because of the android rng bug?  
> **username_0**: I agree with James that it would be nice to have a source on "some people lost coins". Even with that, though, it sounds like only the people who reused an address lost coins, not even other users of the same buggy pRNG.  
> **username_3**: You can look through this thread here, it talks a lot about the issue with the Android Bitcoin Wallet https://bitcointalk.org/index.php?topic=271486.0/ . About 55 bitcoins were stolen , and it is verifiable since they come from addresses that were compromised due to bad signatures.  

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