Pay someone w/out their address?

[Kais]

There is a site, bitlotto.com, that pays out a winner to the lottery without even asking for a return address to send the payment to...How do they know which address to send to?

How do I find the address of someone who sent me some coins?

[SgtSpike]

There is a site, bitlotto.com, that pays out a winner to the lottery without even asking for a return address to send the payment to...How do they know which address to send to?

How do I find the address of someone who sent me some coins?

They send it back to the address that they were paid from.  So I might pay them from 123456789123456789, then when I win, they'll send me the jackpot back to that same address.

That's why they say don't use an online wallet for it - because the jackpot will be given to the online wallet company, not back to you.

[Kais]

So how do I find that address? Is it in my BTC client, or do   I have to use blockexplorer or something?

[SgtSpike]

Yes, use blockexplorer.  It won't show you what address the coins came from in the client GUI.

[Kais]

Sorry, I guess I don't yet understand blockexplorer either. When I search for a payment I received, there are many different addresses. Which one should I use to send the return payment to?

Thanks for your help!!

[SgtSpike]

Well, that's the difficult part...

How much did this person send, and what address did they send it to?  If you can't share that information, then I'm not sure I can help you.  It's difficult to explain over the forum without seeing the actual transaction.

[Pieter Wuille]

Bitcoin transactions do not have a from address. There is only optionally some identifiable address the used coins were last sent to, but you shouldn't rely on that. The client does not show you because it is a fallacy to think that bitcoin transactions have a return address.

[JoelKatz]

If there is one, you can use the address the 'change' was sent to. For example, say I pay you 1 bitcoin. My transaction will typically look like this:

In:
1 or more transactions that total more than 1 BTC

Out:
1BTC -> you
Rest -> change back to me

You can consider the address the change went to as belonging to the sender. Of course, if the sender was sending bitcoins to more than one place, this won't work.

[SgtSpike]

If there is one, you can use the address the 'change' was sent to. For example, say I pay you 1 bitcoin. My transaction will typically look like this:

In:
1 or more transactions that total more than 1 BTC

Out:
1BTC -> you
Rest -> change back to me

You can consider the address the change went to as belonging to the sender. Of course, if the sender was sending bitcoins to more than one place, this won't work.

Any address that the coins are coming from would be owned by the person who sent them though.  You could use any address out of that transaction, really.  As long as they didn't use sendmany to conduct it, all addresses in the transaction either belong to yourself or to the other party.

[Pieter Wuille]

This assumes that the address is controlled by the user and not some e-wallet, and that he will keep its corresponding private key for eternity. That's a pretty strong requirement.

There is one rule only really: only send to an address you know the owner wants you to.

[bitlotto]

This assumes that the address is controlled by the user and not some e-wallet, and that he will keep its corresponding private key for eternity. That's a pretty strong requirement.

There is one rule only really: only send to an address you know the owner wants you to.

Exactly. That's why I make sure to mention on my bitlotto instructions that people back up their wallet after buying a ticket. Just in case they lose it.

Unless you know the details, there is a risk about sending it back to the same address. You have to make sure they didn't use an Ewallet AND make sure they still have the wallet! People delete empty wallets. Or use an old backup that may not have that key anymore. Sending to the "change" address would also only work if they didn't use an Ewallet. You pretty much have to know those things before you proceed.