My bank already knows my email address and phone number(s).
I would expect that the easiest way of doing this would be for the banks to handle it all - when I buy something my bank gets a receipt signed by the shop's bank to say that I did buy item X at time Y at location Z. My bank could perhaps then countersign the receipt to link that strongly to my identity.
It would be particularly good if the format included a standard representation of tax paid (VAT etc.) - would make filling out expense claims so much easier.
I would expect that the easiest way of doing this would be for the banks to handle it all - when I buy something my bank gets a receipt signed by the shop's bank to say that I did buy item X at time Y at location Z. My bank could perhaps then countersign the receipt to link that strongly to my identity.
It would be particularly good if the format included a standard representation of tax paid (VAT etc.) - would make filling out expense claims so much easier.