An electronic payment system is needed for compensation for information, goods and services provided through the Internet - such as access to copyrighted materials, database searches or consumption of system resources - or as a convenient form of payment for external goods and services - such as merchandise and services provided outside the Internet. it helps to automate sales activities, extends the potential number of customers and may reduce the amount of paperwork.
security: payment systems are very likely to become a target for criminal attacks.flexibility: different models for different situations (anonymity, accountability, risk).computational efficiency: support for micropayment; per-transaction cost must be small enough so that they are insignificant.
secure (or non-secure) presentation: the customer provides credit card information over a secure (or even clear) transportation means.
customer registration: the customer gets a password or digital signature based on a credit card (hides the credit card information from the merchant, but still clears through the credit card).
credit-debit instruments: similar to customer registration but only one bill per month either through credit card or debit check.
electronic currency: this method has potential for anonymity but requires tamper resistant hardware.
server scrip: the customer gets a kind of coupons from an agent that can be spend only with one particular merchant. this reduces the risk of double spending and allows off-line transactions.
direct transfer: the customer initiates the transfer of funds to the account of the merchant. this method provides no anonymity.
collection agent: the merchant refers the customer to a third party who collects payment using one of the methods mentioned above.