Digital Payment

None of the schemes covered so far is well suited for Digital Payment

Payment systems have diverse requirements

For low-cost items (information):

Transaction must be quick and easy
Strong security is less important

For higher-cost items (hard goods):

Non-repudiation is important (vendor-signed receipts)
Off-line payment aproval may be necessary

Other Issues:

Which comes first? The payment or the goods?

How much new software/hardware is required to use a payment scheme?

Who manages the accounts?

What allowances for privacy are made?