How can I prove that I sent Bitcoins to someone?

[LaOrtega]

Hi there.

Lets say that I sent some BTC from my wallet to someone's address.  How can I prove to the person that I was the one who sent the bitcoins?

I can look up their address and see that my bitcoins arrived there, but how do i prove to them that those were indeed the bitcoins from my wallet and not some from someone else.

I'm sure this has been answered before, but when I type in words like "proof" and "transaction" into the search bar too many posts are returned.

Can someone please help me out?

Thanks.

[BurtW]

Hi there.

Lets say that I sent some BTC from my wallet to someone's address.  How can I prove to the person that I was the one who sent the bitcoins?

I can look up their address and see that my bitcoins arrived there, but how do i prove to them that those were indeed the bitcoins from my wallet and not some from someone else.

I'm sure this has been answered before, but when I type in words like "proof" and "transaction" into the search bar too many posts are returned.

Can someone please help me out?

Thanks.

The Bitcoins were sent from an address you control so you can sign a message proving that you have the private key of the address that the coins were sent from.

Like this message:

I sent 0.869 BTC from 1BurtWEejbnKeBRsvcydJvsNztB1bXV5iQ to 1HJzFEUPybQJeEJz8h292jSgtYg1XPyHR4  2013-04-24 22:36:41

Signature:  HIZxlOZ7erYDmvj8mKn3vInL7/75nQcGQzMmJ9ye4QCnFf0cfLzAI6vAcUcvdyKBm/5+cYftTOSd+CDV1wdi0ck=

Now all you need is the message text, the signature and the public Bitcoin address (1BurtWEejbnKeBRsvcydJvsNztB1bXV5iQ) to verify the message.

If you enter these three things into the client in the verify message dialog it will verify that I do in fact have the private key for the public address 1BurtWEejbnKeBRsvcydJvsNztB1bXV5iQ

[DannyHamilton]

- snip -
The Bitcoins were sent from an address you control so you can sign a message proving that you have the private key of the address that the coins were sent from.
- snip -

Unfortunately, the Bitcoin-Qt wallet doesn't display the addresses that it sends "change" to.

If all the bitcoins in your transaction came from "change" addresses, there is nothing in the user interface that makes it easy to sign a message using any of those addresses.

It can be done, but not without significant technical know-how.

It would be nice if a future version of the wallet would address this issue.

[ahgadget]

Great explanation - thanks!