Clock Gating (CG) is a well known technique to reduce dynamic power consumption by stopping the clock to avoid unnecessary transitions in synchronous circuits. The abilities of different CG-styles to save power at a flip-flop level, depending on the input activity, are analysed in this paper. Also, since conventional CG techniques usually do not take into account leakage power, some optimization procedures and guidelines are presented for leakage reduction. Focusing on those structures that do not need a latch to remove undesired transitions in gated clock, a leakage value of a fourth of the original one is achieved without degradation in timing performances.

One of the best methods to improve the security of cryptographic systems used to exchange sensitive information is to attack them to find their vulnerabilities and to strengthen them in subsequent designs. Trivium stream cipher is one of the lightweight ciphers designed for security applications in the Internet of things (IoT). In this paper, we present a complete setup to attack ASIC implementations of Trivium which allows recovering the secret keys using the active non-invasive technique attack of clock manipulation, combined with Differential Fault Analysis (DFA) cryptanalysis. The attack system is able to inject effective transient faults into the Trivium in a clock cycle and sample the faulty output. Then, the internal state of the Trivium is recovered using the DFA cryptanalysis through the comparison between the correct and the faulty outputs. Finally, a backward version of Trivium was also designed to go back and get the secret keys from the initial internal states. The key recovery has been verified with numerous simulations data attacks and used with the experimental data obtained from the Application Specific Integrated Circuit (ASIC) Trivium. The secret key of the Trivium were recovered experimentally in 100% of the attempts, considering a real scenario and minimum assumptions.

The learning of digital design at the RT level by the students improves with practical work, which can be developed in teams, allow both the gradual advance of complexity as the learning progresses, and the proposal to be attractive to them, such as playing simple games. FPGAs and development boards offer a very suitable platform for the implementation of these designs. This paper presents a work in the Advanced Digital Design course (4th year of the Degree) consisting of the construction of a slightly adapted version of the game “Simon Says” in which the player must memorize a sequence that becomes more difficult for as levels pass. The work, which occupies the second half of the semester, is carried out by teams of three students and must have a demonstrator implemented on a Digilent Nexys4-DDR board.

Different techniques used by a CAD tool that automatically optimize power consumption at gate-level circuit have been investigated in terms of switching noise generation. Such techniques, clock-gating, sleep-mode and others at a gate-level are usual saving power techniques, but are rarely applied to switching noise reduction. The reduction of peaks in supply current is of great interest due to their impact in sensitive parts of a circuit. An estimation of these peaks has been done at a gate level by two different tools (PrimePower and NanoSim, both from Synopsys) providing both the power supply current waveform along time, the average and the peak power for different synthesized circuits to check the effectiveness of such low-power techniques for switching noise reduction. As conclusions, although both tools provide an estimation of peak power, only NanoSim gives accurate values, and how these optimization techniques for low-power are, in general, useful for switching noise reduction.

A new technique to build edge-triggered flip-flops based on the use of ‘weak’ transistors is presented. This technique can be applied to most CMOS differential latches with only some further design considerations. Despite of hardware costs, resulting flip-flops are very suited for high-performance and low-noise applications.