Hard instances of the constrained discrete logarithm problem

The discrete logarithm problem (DLP) generalizes to the constrained DLP, where the secret exponent x belongs to a set known to the attacker. The complexity of generic algorithms for solving the constrained DLP depends on the choice of the set. Motivated by cryptographic applications, we study explicit construction of sets for which the constrained DLP is hard. We draw on earlier results due to Erdos et al. and Schnorr, develop geometric tools such as generalized Menelaus' theorem for proving lower bounds on the complexity of the constrained DLP, and construct explicit sets with provable non-trivial lower bounds.