A major step is required to integrate critical legal requirements into e-tendering system design. The current systems using ad-hoc security mechanisms do not meet the legal requirements for forming a complex electronic contract. This paper analyses the etendering process and its legal obligations. The mapping of these obligations to security policies has identified a set of essential security services (mechanisms) for e-tendering systems, with particular emphasis on the contract forming process. These essential security services provide a promising solution for a reliable etendering system.