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Recent Submissions
Compiler Support for Constant-Time Programs in LLVM
(University of Waterloo, 2025-07-21) Aghakishiyev, Mehdi
Side-channel attacks aim to extract sensitive information by monitoring the additional information generated during program execution, such as execution time or power consumption. Certain coding patterns, such as using secret data in control flow and memory addressing instructions, cause the execution time of the program to vary based on secret input, making the program vulnerable to timing-based side-channel attacks. Constant-time programming offers a defense against such attacks; however, it is difficult to implement manually as it requires tracking secret data through complex program logic.
In this thesis, we propose an automated approach to generate constant-time programs based on static analysis and program transformations. First, we use taint tracking to monitor the flow of secret input through the program and mark branching and memory addressing instructions that depend on secret data. Then, we apply program transformation techniques such as branch linearization to remove these dependencies and produce constant-time code. We perform our analysis and transformations on LLVM IR and implement our tool as part of the LLVM Pass Infrastructure.
To evaluate our tool’s effectiveness, we apply our analysis and transformations to programs from the OISA benchmark. We validate our results through BliMe, an architecture performing hardware-enforced taint tracking to prevent side-channel attacks.
Point of collapse and continuation methods for large AC/DC systems
(Institute of Electrical and Electronics Engineers (IEEE), 2002-08-06) Canizares, Claudio A.; Alvarado, Fernando L.
The implementation of both point of collapse (PoC) methods and continuation methods for the computation of voltage collapse points (saddle-node bifurcations) in large AC/DC power systems is described. The performance of these methods is compared for real systems of up to 2158 buses. Computational details of the implementation of the PoC and continuation methods are detailed, and the unique problems encountered due to the presence of high-voltage direct-current (HVDC) transmission, area interchange power control, regulating transformers, and voltage and reactive power limits are discussed. The characteristics of a robust PoC power flow program are presented, and its application to detection and solution of voltage stability problems is demonstrated.
Calculating optimal system parameters to maximize the distance to saddle-node bifurcations
(Institute of Electrical and Electronics Engineers (IEEE), 2002-08-06) Canizares, Claudio A.
This paper presents a new methodology to calculate parameters of a nonlinear system, so that its distance to a saddle-node bifurcation is maximized with respect to the particular parameters that drive the system to bifurcation. The technique is thoroughly justified, specifying the conditions when it can be applied and the numeric mechanisms to obtain the desired solutions. A comparison is also carried out between the proposed method and a known methodology to determine closest saddle-node bifurcations in a particular power system model, showing that the new technique is a generalization of the previous method. Finally, applications to power systems are discussed, particularly regarding the design of some FACTS devices, and a simple generator-line-load example is studied to illustrate the use of the proposed technique to determine the optimal shunt and/or series compensation to maximize distances to voltage collapse. The effect of the optimal compensation on the stability of the sample system is also analyzed.
Comparison of PSS, SVC, and STATCOM controllers for damping power system oscillations
(Institute of Electrical and Electronics Engineers (IEEE), 2003-05-13) Mithulananthan, N.; Canizares, Claudio A.; Reeve, John; Rogers, Graham J.
This paper discusses and compares different control techniques for damping undesirable interarea oscillation in power systems by means of power system stabilizers (PSS), static VAr compensators (SVCs), and shunt static synchronous compensators (STATCOMs). The oscillation problem is analyzed from the point of view of Hopf bifurcations, an "extended" eigenanalysis to study different controllers, their locations, and the use of various control signals for the effective damping of these oscillations. The comparisons are based on the results obtained for the IEEE 50-machine, 145-bus test system, which is a benchmark for stability analysis.
Reactive Power and Voltage Control in Distribution Systems With Limited Switching Operations
(Institute of Electrical and Electronics Engineers (IEEE), 2009-03-31) Liu, M.B.; Canizares, C.A.; Huang, W.
An algorithm based on a nonlinear interior-point method and discretization penalties is proposed in this paper for the solution of the mixed-integer nonlinear programming (MINLP) problem associated with reactive power and voltage control in distribution systems to minimize daily energy losses, with time-related constraints being considered. Some of these constraints represent limits on the number of switching operations of transformer load tap changers (LTCs) and capacitors, which are modeled as discrete control variables. The discrete variables are treated here as continuous variables during the solution process, thus transforming the MINLP problem into an NLP problem that can be more efficiently solved exploiting its highly sparse matrix structure; a strategy is developed to round these variables off to their nearest discrete values, so that daily switching operation limits are properly met. The proposed method is compared with respect to other well-known MINLP solution methods, namely, a genetic algorithm and the popular GAMS MINLP solvers BARON and DICOPT. The effectiveness of the proposed method is demonstrated in the well-known PG&E 69-bus distribution network and a real distribution system in the city of Guangzhou, China, where the proposed technique has been in operation since 2003.