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Two level efficient user authentication scheme

User authentication procedures are a computer system's first line of defense against malicious attacks that could potentially jeopardize its availability and reliability. Computational complexity considerations may prevent system designers from implementing efficient authentication procedures. This paper presents a robust two level authentication procedure is presented that is highly efficient and suitable for multi-user systems. Authentication is attained in only a single cycle of exchanges between the user and the authentication system. Further advantages arise from the fact that with the proposed technique, it is not necessary to store lists of passwords and therefore the overhead caused in systems with large numbers of registered users is minimal. The proposed architecture is shown to be reliable while creating significant economies in the amount of information that needs to be stored. These facts therefore render the architecture highly suitable for hardware implementations.