Both quantum-dot cellular automata (QCA) and reversible logic are emerging technologies that are promising alternatives to overcoming the scaling and heat dissipation issues, respectively, in the current CMOS designs. Here, the fundamentals of QCA and reversible logic are studied; the feasibility of incorporating reversible logic in QCA designs is also demonstrated. Based on two existing designs, an improved version of the reversible gates, namely the Feynman Gate and the Toffoli Gate, were implemented in QCA technology using QCADesigner. The proposed design of the QCA-based Feynman Gate is faster by ½ cycle as compared to the existing design; while the proposed Toffoli Gate has the same latency as the existing design but it is readily to be cascaded into a more complex design. A 4-bit ripple carry adder in QCA is then designed using the proposed Feynman and Toffoli gates to realize a reversible QCA full adder. This 4-bit QCA adder with reversible logic consists of 2030 QCA cells, has a latency of 7 clock cycles and 8 garbage outputs.

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<span>Cryptographic applications require numbers that are random and pseudorandom. Keys must be produced in a random manner in order to be used in common cryptosystems. Random or pseudorandom inputs at different terminals are also required in a lot of cryptographic protocols. For example, producing digital signatures using supporting quantities or in verification procedures that requires generating challenges. Random number generation is an important part of cryptography because there are flaws in random number generation that can be taken advantage by attackers that compromised encryption systems that are algorithmically secure. True random number generators (TRNGs) are the best in producing random numbers. This paper presents a True Random Number Generator that uses memristor based ring oscillators in the design. The designs are implemented in 0.18 µm complementary metal oxide semiconductor (CMOS) technology using LT SPICE IV. Different window functions for the memristor model was applied to the TRNG and compared. Statistical tests results of the output random numbers produced showed that the proposed TRNG design can produce random output regardless of the window function.</span>

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