A vendor I am dealing with wants me to make a donation to a third party organization (e.g., Greenpeace) in order to be eligible for certain benefits in his shop. The vendor is willing to accept an email receipt of payment to this organization over PayPal as proof that I have done this. I have done this, and provided the vendor the email as proof (which he as accepted), but it occurs to me that it is apparently impossible for the vendor to verify I haven't altered the content of the email receipt to make it look like I have made a payment that I haven't. So either the vendor makes the payment for me, in which case I have to trust the vendor's honesty, or the vendor has to trust that I am not manipulating the email receipt. This seems problematic.
Is there a way for PayPal to incorporate, say, a digitally signed QR representation of key facts of a transaction into email receipts, such that vendors may be assured, with strong cryptographic backing, that the key facts presented in human-readable email have not been altered; or alternately, is there a way to directly "share" with the vendor the fact-of transaction with a third party (e.g. Greenpeace), without resorting to alterable media such as email?
