Yes, it's basically one message sent from the buyer's computer that includes a product code, payment info and a digital signature that authenticates the message. The digital signature is a hash of the info in the message based on a network key.
NewEgg is a great company. If someone has slam-dunk prior art for this, they should forward it on to them. Just yesterday I ordered a hard drive enclosure from them and it came the same day with the cheapest shipping! Outstanding.
Here is a sample claim:
A network-based system for processing payment messages, comprising:
a buyer computer; and
the buyer computer and the payment computer being interconnected by a public packet switched computer network;
the buyer computer being programmed to send to the payment computer a payment message for purchasing a product in response to a user request,
the payment message comprising a product identifier identifying the product,
the payment message comprising a universal resource locator containing all information required by the payment computer for authorizing purchase of the product and an authenticator that comprises a digital signature based on a cryptographic key;
the payment computer being programmed to receive the payment message and to authorize, based on the payment message, purchase of the product.