"Applying Reversible Logic to Cryptographic Hardware"

Himanshu Thapliyal
International Institute of Information Technology


Differential Power Analysis (DPA) presents a major challenge to mathematically-secure cryptographic protocols. Attackers can break the encryption by measuring the energy consumed in the working digital circuit. To prevent this type of attack, this paper proposes the use of reversible logic for designing the ALU of a cryptosystem. Ideally, reversible circuits dissipate zero energy. Thus, it would be of great significance to apply reversible logic to designing secure cryptosystems. As far as is known, this is the first attempt to apply reversible logic to developing secure cryptosystems. In a prototype of a reversible ALU for a crypto-processor, reversible designs of adders and Montgomery multipliers are presented. The reversible designs of a carry propagate adder, four-to-two and five-to-two carry save adders are presented using a reversible TSG gate. One of the important properties of the TSG gate is that it can work singly as a reversible full adder.  In order to design the reversible Montgomery multiplier, novel reversible sequential circuits are also proposed which are integrated with the proposed adders to design a reversible modulo multiplier. Nowadays, ECC (Elliptic Curve Cryptography) is major attraction compared to RSA as it offers equal security for a smaller key size thereby reducing processing overhead. The benefits of ECC, when compared with classical cryptosystems such as RSA, include: higher speed, lower power consumption and smaller certificates, which are especially useful for wireless applications. The major time and power consuming arithmetic operations operation in ECC are point additions and doubling. In order to have the big picture of reversible cryptographic hardware, the author has also demonstrated the reversible design of point doubling hardware. It is intended that this paper will provide a starting point for developing cryptosystems secure against DPA attacks.

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