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Author Topic: Bitcoin client with this feature  (Read 2108 times)
Weent1987
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July 21, 2015, 05:53:12 AM
 #1

From https://bitcoin.org/en/protect-your-privacy

"You can use a Bitcoin client like Bitcoin Core that makes it difficult to track your transactions by creating a new change address each time you send a payment. For example, if you receive 5 BTC on address A, and you later send 2 BTC to address B, the remaining change must be sent back to you. Some Bitcoin clients are designed to send the change to a new address C in such a way that it becomes difficult to know if you own Bitcoin address B or C."

which client has this feature?
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Muhammed Zakir
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July 21, 2015, 09:13:51 AM
 #2

Desktop wallets: Electrum, Armory and Bitcoin Core. I think Multibit HD use unused address for change but I am not sure about it.

In fact, al most all of the HD wallets use new address to receive change unless you change default settings or you manually choose change address.

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July 21, 2015, 10:23:48 PM
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Both Electrum and Armory has this feature enabled by default, although you can turn this off (if you do wish to turn it off for one transaction then you will need to reenable it prior to sending another transaction), and AFAIK bitcoin core does not allow you to disable this.

You should note however, that if anyone who you trade with (either send to or receive from) were to ever start reusing their addresses (even once, although to have a major effect, it would need to happen more often), then the privacy you get by using change addresses properly is diminished, so I would not rely on this alone to be an effective way to maintain your privacy when there is a lot at stake to avoiding others knowing what you are up to
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July 23, 2015, 05:58:34 PM
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I wonder why change addresses were implemented as a way for more privacy. In fact it's a tool to slowly find out all the addresses one owns in a wallet. I have it disabled since a long time and think about privacy on my own. Connecting your addresses is way to easy otherwise.
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July 24, 2015, 03:48:53 AM
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I wonder why change addresses were implemented as a way for more privacy. In fact it's a tool to slowly find out all the addresses one owns in a wallet. I have it disabled since a long time and think about privacy on my own. Connecting your addresses is way to easy otherwise.
If change addresses are used properly then it should be difficult to know with certainty which other addresses a certain person owns. If you reuse addresses then an attacker will know with much greater certainty how much bitcoin you have, and the privacy of those that you trade with will be diminished.
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August 01, 2015, 02:15:41 PM
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I wonder why change addresses were implemented as a way for more privacy. In fact it's a tool to slowly find out all the addresses one owns in a wallet. I have it disabled since a long time and think about privacy on my own. Connecting your addresses is way to easy otherwise.
If change addresses are used properly then it should be difficult to know with certainty which other addresses a certain person owns. If you reuse addresses then an attacker will know with much greater certainty how much bitcoin you have, and the privacy of those that you trade with will be diminished.

I think it is relatively easy to guess which is a change address.

The big problem with them is that all the change money on them has to be sent out too, at some point. And that normally, when you don't take care, in a transactions where all the outputs to the change addresses become inputs in a transaction. Voila... all change addresses identified.
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August 04, 2015, 11:10:47 PM
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I think it is relatively easy to guess which is a change address.
If your trading partners engages in the practice of reusing addresses then it should be easy to determine which addresses of your are change addresses. This is even true to some extent if your trading partner's trading partner reuses addresses.

However if everyone you trade with uses a fresh address each time they receive bitcoin then there would be very little information available to an attacker that would allow them to conclude which addresses belong to the same person.
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August 05, 2015, 09:40:34 AM
 #8

As for mobile wallets: Mycelium (Android) and breadwallet (iOS) are HD wallets, they provide this feature as well.

Theoretically, you may be able to guess what change addresses belong to the same user. But after a few transactions, it looks like this:



Now which addresses on the right hand side still belong to the original owner? Nobody can tell.

In theory, there's no difference between theory and practice. In practice, there is.
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omahapoker
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August 08, 2015, 09:36:48 AM
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I think it is relatively easy to guess which is a change address.
If your trading partners engages in the practice of reusing addresses then it should be easy to determine which addresses of your are change addresses. This is even true to some extent if your trading partner's trading partner reuses addresses.

However if everyone you trade with uses a fresh address each time they receive bitcoin then there would be very little information available to an attacker that would allow them to conclude which addresses belong to the same person.

You are right. And yes, there still are surprisingly many services like that. For example purse.io. I don't know why they do it that way but it surely is very bad for privacy. I asked them to change that but they only admitted that i have good knowledge of bitcoin but didn't change it till now.
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August 08, 2015, 09:40:48 AM
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As for mobile wallets: Mycelium (Android) and breadwallet (iOS) are HD wallets, they provide this feature as well.

Theoretically, you may be able to guess what change addresses belong to the same user. But after a few transactions, it looks like this:



Now which addresses on the right hand side still belong to the original owner? Nobody can tell.

But transactions doesn't look that way that 3 outputs are done. That's rather special.

They normally look like one output to a target address and one output to the input address or a change address. Then when you have one output with many decimal values and one with mostly zero at the end then you can guess pretty good that the output with the many decimal values is your change address.

Even if you can't guess. At one point you have many dust in change addresses and you need to send it out. Doing that in one transaction saves fee but it could, on the way reveal ALL change addresses you used as yours and all addresses you used to fill that change addresses.

It's really something to be cautious with.
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