Secure Electronic Transaction (SET) was a standard protocol for securing credit card transactions over insecure networks, specifically, the Internet. SET was not itself a payment system, but rather a set of security protocols and formats that enable users to employ the existing credit card payment infrastructure on an open network in a secure fashion. However, it failed to gain traction. VISA now promotes the 3-D Secure scheme.
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SET was developed by SETco, led by VISA and MasterCard (and involving other companies such as GTE, IBM, Microsoft, Netscape, RSA, Safelayer --formerly SET Projects-- and VeriSign) starting in 1996. SET was based on X.509 certificates with several extensions. The first version was finalised in May 1997 and a pilot test was announced in July 1998.
SET allowed parties to cryptographically identify themselves to each other and exchange information securely. SET used a blinding algorithm that, in effect, would have let merchants substitute a certificate for a user's credit-card number. If SET were used, the merchant itself would never have had to know the credit-card numbers being sent from the buyer, which would have provided verified good payment but protected customers and credit companies from fraud.
SET was intended to become the de facto standard of payment method on the Internet between the merchants, the buyers, and the credit-card companies. Despite heavy publicity, it failed to win market share. Reasons for this include:
To meet the business requirements, SET incorporates the following features:
A SET system includes the following participants:
The sequence of events required for a transaction are as follows:
An important innovation introduced in SET is the dual signature. The purpose of the dual signature is the same as the standard electronic signature: to guarantee the authentication and integrity of data. It links two messages that are intended for two different recipients. In this case, the customer wants to send the order information (OI) to the merchant and the payment information (PI) to the bank. The merchant does not need to know the customer's credit card number, and the bank does not need to know the details of the customer's order. The link is needed so that the customer can prove that the payment is intended for this order.
The message digest (MD) of the OI and the PI are independently calculated by the customer. The dual signature is the encrypted MD (with the customer's secret key) of the concatenated MD's of PI and OI. The dual signature is sent to both the merchant and the bank. The protocol arranges for the merchant to see the MD of the PI without seeing the PI itself, and the bank sees the MD of the OI but not the OI itself. The dual signature can be verified using the MD of the OI or PI. It doesn't require the OI or PI itself. Its MD does not reveal the content of the OI or PI, and thus privacy is preserved.