Proof of Origination of Transaction

[jgm]

For a given transaction, how can I prove that I was the originator?

Given that I hold the private key of the originator for a given transaction, can I produce some sort of signature after the fact that proves this, or would I have to originate an additional transaction to provide proof?

[DannyHamilton]

- snip -
can I produce some sort of signature after the fact that proves this
- snip -

Yes.

Some clients/wallets, such as Bitcoin-Qt, have this ability built in.

[jgm]

- snip -
can I produce some sort of signature after the fact that proves this
- snip -

Yes.

Some clients/wallets, such as Bitcoin-Qt, have this ability built in.

Thanks for the answer; I'm curious as to if there is any way in which additional information can be added to the transaction prior to signature generation, to allow for a challenge/response from the recipient?