Secure electronic transaction (SET) is a significant e-commerce protocol designed to improve the security of credit card purchases. In this paper we discuss various security measures and protocols which are used till date and are still used for the security of online transaction in which electronic cash flows from buyer to the supplier or merchant. Various issues discussed in this paper are SET protocol, Authenticated and Key Agreement for P2P-Based Networks, Mutual Authentication between Cardholder and Merchant, Biometric Mechanism for enhanced Security of Online Transaction, Using a Mobile Device to Enhance Customer Trust in the Security of Remote Transactions, Digital content mediator for secure P2P online transactions, Sensitive Data Transfer Security Model finally we will see the SMS-Based Authentication Scheme.