Can i re-use BTC adress in my case?

[Mikcik]

Hello i have a cold storage with electrum wallet. (not a paper wallet).

I have a question - i wanna sent Bitcoin to an adress for the 1st time in my life . I just wanna sent like 50 USD worth of it to an exchange adress, just for a test how it works... When i spent from any adress i HAVE TO spent the whole ammount - the ammount im sending to someone else and tha remaining value which is called "change" to some of MY adress. I know that. I know when spending from an adress i always have to spent the whole ammount (to different adresses). I understand bitcoin was built this way due to some technical stuff.

But can i sent the change to my original adress? It should be possible and Electrum should allow me to do so, correct?

1) I dont care at this point about anonymity i just wanna test sending the 50 USD via BTC to an exchange and than back. So anonymity doesnt concern me at this point.
2) When spending from adress from which i already spent my future transactions will be a bit bigger in terms of data size (bytes, or kilobytes or whatever) so i might want to pay a higher fee but i dont care about that much.

So in my example, for this one time, i should be OK with reusing the adress, correct?  (or is there some hidden danger im not aware of)?

[AdolfinWolf]

Yes, this is possible.

Although i wouldn't recommend it as it poses a "huge" risk to your privacy, and that of the bitcoin network. ( due to everyone knowing who owns what).

See https://bitcoin.stackexchange.com/questions/12746/can-a-bitcoin-transaction-have-the-same-address-for-input-and-output?rq=1

This transaction for example is using both the change and spent adress as one adress -> https://blockchain.info/tx-index/b345c51064074f5d6c0e11187326567765eb4fa3236ca1be440ccb5745775238
https://bitcoin.stackexchange.com/a/12747/61384

[Mikcik]

Yes, this is possible.

Although i wouldn't recommend it as it poses a "huge" risk to your privacy, and that of the bitcoin network. ( due to everyone knowing who owns what).

See https://bitcoin.stackexchange.com/questions/12746/can-a-bitcoin-transaction-have-the-same-address-for-input-and-output?rq=1

This transaction for example is using both the change and spent adress as one adress -> https://blockchain.info/tx-index/b345c51064074f5d6c0e11187326567765eb4fa3236ca1be440ccb5745775238
https://bitcoin.stackexchange.com/a/12747/61384

thanks... so in electrum waller somewhere there will be field in the "sent" tab which will say "change" and there i wil enter the same adress from which im sending, correct?
Regarding the security it doesnt matter as far as i understand it, since its only for 1 transaction, in future transactions i will be using another adresses, so it really doesnt matter for one time, does it?

[mocacinno]

Yes, this is possible.

Although i wouldn't recommend it as it poses a "huge" risk to your privacy, and that of the bitcoin network. ( due to everyone knowing who owns what).

See https://bitcoin.stackexchange.com/questions/12746/can-a-bitcoin-transaction-have-the-same-address-for-input-and-output?rq=1

This transaction for example is using both the change and spent adress as one adress -> https://blockchain.info/tx-index/b345c51064074f5d6c0e11187326567765eb4fa3236ca1be440ccb5745775238
https://bitcoin.stackexchange.com/a/12747/61384

thanks... so in electrum waller somewhere there will be field in the "sent" tab which will say "change" and there i wil enter the same adress from which im sending, correct?
Regarding the security it doesnt matter as far as i understand it, since its only for 1 transaction, in future transactions i will be using another adresses, so it really doesnt matter for one time, does it?

I don't think there is a "change" field in the "sent" tab. I think you have to go to your preferences and make sure the field "use change address" in the "transactions" tab is unchecked...

However, i'm still not sure why you would do such a thing...

[kelvinyong]

From what I know is that, you can use it multiple times. I started not long ago and have been sending and receiving from my coinpot wallet to exchanges and gamble sites. But there are certain crypto like monero and certain coins that requires certain weird address which I'm not so clear of as well.

[mocacinno]

From what I know is that, you can use it multiple times. I started not long ago and have been sending and receiving from my coinpot wallet to exchanges and gamble sites. But there are certain crypto like monero and certain coins that requires certain weird address which I'm not so clear of as well.

You can re-use those addresses to, but like AdolfinWolf already said: you're compromising your anonimity... If you're fine with that AND you're using a recent wallet, there should be no problem with address re-use. In the past, there were problems with signatures re-using the same R value, in which case multiple signatures could be used to calculate your private key, but in recent times, i don't think there are wallets that still have this problem.

The main question remains: why would you re-use a address generated by a HD wallet? Personally, i do re-use my vanity address, but addresses generated by a HD wallet are single-use only.

[odolvlobo]

You didn't explain why ypu want to reuse an address.

1. It is possible to re-use addresses, though there is rarely a good reason.
2. Unless I'm missing something, Electrum doesn't let you specify the change address.
3. The size of a transaction does not depend on which addresses are used.

[digimarketblockchain]

You can use 1 address. They say that using the address repeatedly might be capable of getting hacked.

[AdolfinWolf]

You didn't explain why ypu want to reuse an address.

1. It is possible to re-use addresses, though there is rarely a good reason.
2. Unless I'm missing something, Electrum doesn't let you specify the change address.
3. The size of a transaction does not depend on which addresses are used.

2.
It does actually, simply go to Electrum -> Preferences -> Change adresses, and simply untick it, and it should work/ always send the coins back to the adress they were originally sent from.

This was added as a commit in https://github.com/spesmilo/electrum/commit/e123774ea8d2b9f30c958c7710cfe797bb7cd4b2, before that, it would still be possible using the command line.


If you want to actually set it to a custom change adress, you should check this out -> https://www.reddit.com/r/Electrum/comments/7bzq7w/is_it_possible_to_define_a_custom_change_address/dpm515j/

[thedarksun]

Possible but don't do this. My friend done something equal to your stiuation and he was close to lose his whole coins, so if you want you can try.

[Mikcik]

You didn't explain why ypu want to reuse an address.

1. It is possible to re-use addresses, though there is rarely a good reason.
2. Unless I'm missing something, Electrum doesn't let you specify the change address.
3. The size of a transaction does not depend on which addresses are used.

3) YOu are wrong AFAIK...adresses which have a lot of inputs (like a public donation adress where people sent you a LOT of small transactions) actually ARE bigger in data size (Kb) and thus they might be more expensive to sent, since in bitcoin you pay sathoshie/per byte. That means the bigger the "adress" (the more inputs or outputs) it has, the biiger its data size is and thus the more you might pay to spent such adress... YOu didnt know this :-O...??

GUYS... wtf... i expect im talking to pros here...
Regarding why i wanna re-use one of my particular adresses is: I have written (that means backuped) the private key on paper on several places and im t lazy to replace all the backupfiles (written on paper) withthe new private key.

[Mikcik]

Also a question, electrum wallet did generate by default 26 adresses (and corresponding private keys). If i sent small ammount of BTC "outside" (to an exchange for example). The "unspent" ammount will be automatically sent to ANY of the remaining 25 adresses it generated, correct? I by default cannot select the where the "unspent ammount", or the "change" will be sent, correct?

And what if i want to sent another (small) ammoutn outside, the "change" will be sent to another unused adress from the remaining 24 adresses electrum generated, correct? What if i sent additional 24 transcations, what then? Electrum will use one of those 26 adresses that it used  before?

[odolvlobo]

You didn't explain why ypu want to reuse an address.

1. It is possible to re-use addresses, though there is rarely a good reason.
2. Unless I'm missing something, Electrum doesn't let you specify the change address.
3. The size of a transaction does not depend on which addresses are used.

3) YOu are wrong AFAIK...adresses which have a lot of inputs (like a public donation adress where people sent you a LOT of small transactions) actually ARE bigger in data size (Kb) and thus they might be more expensive to sent, since in bitcoin you pay sathoshie/per byte. That means the bigger the "adress" (the more inputs or outputs) it has, the biiger its data size is and thus the more you might pay to spent such adress... YOu didnt know this :-O...??

Perhaps I wasn't clear. If your transaction has three inputs, it doesn't matter which addresses are associated with those inputs. Whether they are all different addresses or all the same address, the transaction is the same size.

So, whether someone sends you 0.001 BTC to a single address 1000 times, or 0.001 BTC to 1000 addresses, your transaction sending 1 BTC will be the same size.

[mocacinno]

You didn't explain why ypu want to reuse an address.

1. It is possible to re-use addresses, though there is rarely a good reason.
2. Unless I'm missing something, Electrum doesn't let you specify the change address.
3. The size of a transaction does not depend on which addresses are used.

3) YOu are wrong AFAIK...adresses which have a lot of inputs (like a public donation adress where people sent you a LOT of small transactions) actually ARE bigger in data size (Kb) and thus they might be more expensive to sent, since in bitcoin you pay sathoshie/per byte. That means the bigger the "adress" (the more inputs or outputs) it has, the biiger its data size is and thus the more you might pay to spent such adress... YOu didnt know this :-O...??

GUYS... wtf... i expect im talking to pros here...
Regarding why i wanna re-use one of my particular adresses is: I have written (that means backuped) the private key on paper on several places and im t lazy to replace all the backupfiles (written on paper) withthe new private key.

you don't have to use all unspent outputs... One address can be funded with hundreds of transactions, meaning the private key belonging to that address has to be used to create signatures for transaction spending any combination of those unspent outputs.
You don't have to create one big transaction spending all those unspent outputs at once...
So, it does not matter to the transaction size if you use one unspent output to address A or an unspent output to address B to fund address C.. It does matter how many unspent outputs you use....

Also a question, electrum wallet did generate by default 26 adresses (and corresponding private keys). If i sent small ammount of BTC "outside" (to an exchange for example). The "unspent" ammount will be automatically sent to ANY of the remaining 25 adresses it generated, correct? I by default cannot select the where the "unspent ammount", or the "change" will be sent, correct?

And what if i want to sent another (small) ammoutn outside, the "change" will be sent to another unused adress from the remaining 24 adresses electrum generated, correct? What if i sent additional 24 transcations, what then? Electrum will use one of those 26 adresses that it used  before?

Electrum uses a gap limit... It automatically derives more addresses... It always uses the next unused address, it has a different derivation path for change addresses. So, no, when using electrum as a standard user, the change addresses will not be reused..

[kelvinyong]

So, whether someone sends you 0.001 BTC to a single address 1000 times, or 0.001 BTC to 1000 addresses, your transaction sending 1 BTC will be the same size.
[/quote]

Ohh, that makes sense.