The Internet is becoming an increasingly commercial arena in which payments are rendered for goods and services. This commerce can take a variety of forms from interactiny with a vendor via a World Wide Web browser to ordering by email from a CD-ROM catalog. Typically the shopping or selection phase is followed by a payment phase and then usually by a fulfillment or delivery phase.
Some people use such general secure channel or secure message systems for payments.
Frequently payment involves three or more parties such as a customer, merchant, and bank or payment system, with structured and interlocking messages that incorporate fields best encrypted for parties other than their initial recipient. For these reasons a number of specialized payment protocols have been adopted.