On the Complexity of Random Satisfiability Problems with Planted Solutions

The problem of identifying a planted assignment given a random $k$-satisfiability ($k$-SAT) formula consistent with the assignment exhibits a large algorithmic gap: while the planted solution becomes unique and can be identified given a formula with $O(n\log n)$ clauses, there are distributions over clauses for which the best-known efficient algorithms require $n^{k/2}$ clauses. We propose and study a unified model for planted $k$-SAT, which captures well-known special cases. An instance is described by a planted assignment $\sigma$ and a distribution on clauses with $k$ literals. We define its distribution complexity as the largest $r$ for which the distribution is not $r$-wise independent ($1 \le r \le k$ for any distribution with a planted assignment). Our main result is an unconditional lower bound, tight up to logarithmic factors, for statistical (query) algorithms [M. Kearns, J. ACM, 45 (1998), pp. 983--1006; V. Feldman, E. Grigorescu, L. Reyzin, S. S. Vempala, and Y. Xiao, J. ACM, 64 (2017), pp. 8:1--8:37], matching known upper bounds, which, as we show, can be implemented using a statistical algorithm. Since known approaches for problems over distributions have statistical analogues (spectral, Markov Chain Monte Carlo, gradient-based, convex optimization, etc.), this lower bound provides a rigorous explanation of the observed algorithmic gap. The proof introduces a new general technique for the analysis of statistical query algorithms. It also points to a geometric paring phenomenon in the space of all planted assignments. We describe consequences of our lower bounds to Feige's refutation hypothesis [U. Feige, Proceedings of the ACM Symposium on Theory of Computing, 2002, pp. 534--543] and to lower bounds on general convex programs that solve planted $k$-SAT. Our bounds also extend to other planted $k$-CSP models and, in particular, provide concrete evidence for the security of Goldreich's one-way function and the associated pseudorandom generator when used with a sufficiently hard predicate [O. Goldreich, preprint, ia.cr/2000/063, 2000].


Read More: https://epubs.siam.org/doi/abs/10.1137/16M1078471