Information Theoretic Distinguishers for Timing Attacks with Partial Profiles: Solving the Empty Bin Issue

In any side-channel attack, it is desirable to exploit all the available leakage data to compute the distinguisher’s values. The profiling phase is essential to obtain an accurate leakage model, yet it may not be exhaustive. As a result, information theoretic distinguishers may come up on previously unseen data, a phenomenon yielding empty bins. A strict application of the maximum likelihood method yields a distinguisher that is not even sound. Ignoring empty bins reestablishes soundness, but seriously limits its performance in terms of success rate. The purpose of this paper is to remedy this situation. In this research, we propose six different techniques to improve the performance of information theoretic distinguishers. We study them thoroughly by applying them to timing attacks, both with synthetic and real leakages. Namely, we compare them in terms of success rate, and show that their performance depends on the amount of profiling, and can be explained by a bias-variance analysis. The result of our work is that there exist use-cases, especially when measurements are noisy, where our novel information theoretic distinguishers (typically the soft-drop distinguisher) perform the best compared to known side-channel distinguishers, despite the empty bin situation.

Interband cascade technology for energy-efficient mid-infrared free-space communication

Space-to-ground high-speed transmission is of utmost importance for the development of a worldwide broadband network.Mid-infrared wavelengths offer numerous advantages for building such a system,spanning from low atmospheric attenuation to eye-safe operation and resistance to inclement weather conditions.We demonstrate a full interband cascade system for high-speed transmission around a wavelength of 4.18μm.The low-power consumption of both the laser and the detector in combination with a large modulation bandwidth and sufficient output power makes this technology ideal for a free-space optical communication application.Our proof-of-concept experiment employs a radio-frequency optimized Fabry–Perot interband cascade laser and an interband cascade infrared photodetector based on a type-II InAs/GaSb superlattice.The bandwidth of the system is evaluated to be around 1.5 GHz.It allows us to achieve data rates of 12 Gbit/s with an on–off keying scheme and 14 Gbit/s with a 4-level pulse amplitude modulation scheme.The quality of the transmission is enhanced by conventional pre-and post-processing in order to be compatible with standard error-code correction.

Linewidth narrowing in self-injection-locked on-chip lasers

Stable laser emission with narrow linewidth is of critical importance in many applications,including coherent communications,LIDAR,and remote sensing.In this work,the physics underlying spectral narrowing of self-injection-locked on-chip lasers to Hz-level lasing linewidth is investigated using a composite-cavity structure.Heterogeneously integrated III–V/SiN lasers operating with quantum-dot and quantum-well active regions are analyzed with a focus on the effects of carrier quantum confinement.The intrinsic differences are associated with gain saturation and carrier-induced refractive index,which are directly connected with 0-and 2-dimensional carrier densities of states.Results from parametric studies are presented for tradeoffs involved with tailoring the linewidth,output power,and injection current for different device configurations.Though both quantum-well and quantum-dot devices show similar linewidth-narrowing capabilities,the former emits at a higher optical power in the self-injection-locked state,while the latter is more energy-efficient.Lastly,a multi-objective optimization analysis is provided to optimize the operation and design parameters.For the quantum-well laser,minimizing the number of quantum-well layers is found to decrease the threshold current without significantly reducing the output power.For the quantum-dot laser,increasing the quantum-dot layers or density in each layer increases the output power without significantly increasing the threshold current.These findings serve to guide more detailed parametric studies to produce timely results for engineering design.

Extreme events in quantum cascade lasers

We demonstrate experimentally that mid-infrared quantum cascade lasers(QCLs)operating under external optical feedback exhibit extreme pulses.These events can be triggered by adding small amplitude periodic modulation,with the highest success rate for the case of a pulse-up excitation.These findings broaden the potential applications for QCLs,which have already been proven to be a semiconductor laser of interest for spectroscopic applications and countermeasure systems.The ability to trigger extreme events paves the way for optical neuron-like systems where information propagates as a result of high intensity bursts.