Sending address questions

[Kouye]

I've been playing around with the Bitcoin-QT client, and have a few questions.

I understood that when you send bitcoins to an address, you usually send a chunk of them which are split between the actual recipient and a "pocket change" address of yours.
This is clear. I also know using some modified client, you can force this change address to whatever you want.

What is not clear, is about the sending address.
I understood that the QT client autogenerates an address (or pulls one from a pre-generated list).
So basically, each time you send coins, a new sending address is used.

Sites such as SatochiDice use this auto-generated sending address to send back coins to you.
Which means, I guess, this autogenerated address cannot be used by anyone else and is bound to your client.

Out of curiosity, I tried sending some coins over to an auto-generated address my client used for a week old transaction. And it indeed recognized it as a self-payment, meaning this address (that appears nowhere in the client, which I found on blockchain.info) is actually not only a sending address, but one of my hidden wallet receiving addresses.

• Is that right ?
• If so, is there a timeout after which the address falls back into the pool to be used by another client ?
• If not, if anyone sends coin to a auto-generated sending address I used 6 months ago, would I still receive the coins ?

Now :
https://blockchain.info/fr/address/18CUaepqDiVFMKsfXUXhQi4ULFaCfTbVuJ
If I scroll down to May 1st, I see this guy sent a lot of small amounts of coins (to MiningUnited, if you dig up, which is probably a ponzi scam, please don't use!) using the same sending address.

I've tried to achieve that too, to no avail.
Thought I had a good lead with the client debug console, using the sendfrom command, which allows you to send coins from a specific account, but it still uses random auto-generated address.

So my final question:

• How can I choose the address I'm sending coins with ?

Thanks a lot for reading all this.

[CtmanGer]

Have a problem, too. Don´t know how to change sending address in qt


bought shares for miners (and generated bitcoins will be send only to address that was payed from)

want to have for each different miner I will have shares in, different addresses.
Want to use bitcoin qt only

[J35st3r]

Since nobody is answering this, I'll bump it up for you with what I know ...

Your bitcoin_qt addresses are unique to you. There is no public pool, they are yours and yours alone. The wallet generates 100 addresses when you create it, and uses them in-order as you create transactions and sends the change back to them. Any of them can be used as receiving addresses, but only the first one is shown as your default address. If you do a lot of transactions it will create more addresses. This is IMPORTANT because if you restore an old backup of a wallet it will not have these new addresses and you will LOSE any bitcoin that was sent to them. Keep your backups up to date.

Thee addresses are good for the life of your wallet, so as long as you have it, you will receive any coin sent to them.

Perhaps a clarification. Bitcoin does not actually live in the wallets, it lives in the blockchain (on all of the bitcoin nodes on the network). Your wallet just contains the keys to access your coin (private keys, hidden by default but you can export them, keep them very safe and very secret if you do).

Doing transactions via the debug console is beyond my expertise, you'll have to wait for a real expert to come along for that info.

[Open4lies]

real expert finally here

So my final question:

• How can I choose the address I'm sending coins with ?

You need a client with coin control feature. There is modified bitcoin-qt client as well with "coin control" if you search this forum

[PeterB]

Since nobody is answering this, I'll bump it up for you with what I know ...

Your bitcoin_qt addresses are unique to you. There is no public pool, they are yours and yours alone. The wallet generates 100 addresses when you create it, and uses them in-order as you create transactions and sends the change back to them. Any of them can be used as receiving addresses, but only the first one is shown as your default address. If you do a lot of transactions it will create more addresses. This is IMPORTANT because if you restore an old backup of a wallet it will not have these new addresses and you will LOSE any bitcoin that was sent to them. Keep your backups up to date.

Thee addresses are good for the life of your wallet, so as long as you have it, you will receive any coin sent to them.

Perhaps a clarification. Bitcoin does not actually live in the wallets, it lives in the blockchain (on all of the bitcoin nodes on the network). Your wallet just contains the keys to access your coin (private keys, hidden by default but you can export them, keep them very safe and very secret if you do).

Doing transactions via the debug console is beyond my expertise, you'll have to wait for a real expert to come along for that info.

Thanks for the info.

[Kouye]

Thanks for the answer, I was aware about the 100 addresses, and the process of creation of new ones.
What I still don't know, though, is how to force the sending address when using bitcoin-qt.

If I sent 12 TX, I can compile the list of the 12 sending addresses it used on blockchain.
But if I want my 13th TX to be sent re-using the 6th generated address (and not fetching next one from the 100), it seems impossible using this client.

Is forcing the sending address possible with any offline wallet software ?

[adworker]

Thanks for the answer, I was aware about the 100 addresses, and the process of creation of new ones.
What I still don't know, though, is how to force the sending address when using bitcoin-qt.

If I sent 12 TX, I can compile the list of the 12 sending addresses it used on blockchain.
But if I want my 13th TX to be sent re-using the 6th generated address (and not fetching next one from the 100), it seems impossible using this client.

Is forcing the sending address possible with any offline wallet software ?

From offline mode? Armoury has coin control afaik but didnt tested it.

[Kouye]

From offline mode? Armoury has coin control afaik but didnt tested it.

No I meant just from a wallet software using a local wallet.dat file, not an online stored wallet.
I'll look again into armory, but last time I checked it needed over 4G of RAM to run, and did not seem to have that feature either....
Will check again, thanks!

[J35st3r]

I'll bump you again as I'm interested in the answer too.

Re-reading your OP carefully, I think there is a little confusion about sending addresses and receiving addresses.

In the blockchain there are only transactions which move coin from one (or several) addresses to another (or several) addresses.

So transactions make the distinction between sending or receiving addresses, but the actual coin balance just exists on an address (which is what blockchain explorer shows you).

Now bitcoin_qt tries to hide all this from you by aggregating all the coin on all your addresses into your balance, and when you send some coin it just does it (by whatever heuristic was programmed in). You don't need to know the detail of the transactions, because its just easy

Now with a faucet, they need to be careful as they are sending tiny amounts (dust) so it is important to optimise the transactions, hence you see the same source address many times, unlike bitcoin_qt which sends the entire balance of a source address and splits it between the recipient and the new change address. As for why? ask Satoshi  

If you need to prove a transaction, you need to send from a specific address that you know the public signing key of. This is where I'm getting beyond my knowledge. As was said upthread, there are modified versions of bitcoin_qt that allow you to do this. And the online wallets (and probably the likes of Armoury etc) let you do it too. So let's wait for an expert again and get this resolved properly.

PS Oops, a bit stale (two posts intervening), but here goes anyway.