Abstract
The complexity of computing the solutions of a system of multivariate polynomial equations by means of Gröbner bases computations is upper bounded by a function of the solving degree. In this paper, we discuss how to rigorously estimate the solving degree of a system, focusing on systems arising within public-key cryptography. In particular, we show that it is upper bounded by, and often equal to, the Castelnuovo-Mumford regularity of the ideal generated by the homogenization of the equations of the system, or by the equations themselves in case they are homogeneous. We discuss the underlying commutative algebra and clarify under which assumptions the commonly used results hold. In particular, we discuss the assumption of being in generic coordinates (often required for bounds obtained following this type of approach) and prove that systems that contain the field equations or their fake Weil descent are in generic coordinates. We also compare the notion of solving degree with that of degree of regularity, which is commonly used in the literature. We complement the paper with some examples of bounds obtained following the strategy that we describe.
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Acknowledgements
The authors are grateful to Albrecht Petzoldt for help with MAGMA computations, to Wouter Castryck for pointing out some typos in an earlier version of this paper, and to Marc Chardin, Teo Mora, Christophe Petit, and Pierre-Jean Spaenlehauer for useful discussions on the material of this paper. This work was made possible thanks to funding from Armasuisse.
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Caminata, A., Gorla, E. (2021). Solving Multivariate Polynomial Systems and an Invariant from Commutative Algebra. In: Bajard, J.C., Topuzoğlu, A. (eds) Arithmetic of Finite Fields. WAIFI 2020. Lecture Notes in Computer Science(), vol 12542. Springer, Cham. https://doi.org/10.1007/978-3-030-68869-1_1
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