- FatBrain creates a form that will be filled in by a Alice and
sent on to EasyPay.
- FatBrain signs all of the form except for shipping address and
credit card information, which is filled in by Alice.
- Alice fills in the form, encrypts the payment authorization
element in a key shared with EasyPay, and returns it to
FatBrain.
- FatBrain processes the form and confirms the integrity of the
order (the book title and price) and passes the encrypted credit
card info to EasyPay.
This protocol is faulty, but it demonstrates the use of
selective signing and encryption.
