Character sums with exponential functions

Abstract

Let ϑ be an integer of multiplicative order t≥1 modulo a prime p. Sums of the formare introduced and estimated, with a sequence such that kz1, …, kzT is a permutation of z1, …, zT, both sequences taken modulo t, for sufficiently many distinct modulo t values of k. Such sequences includexn for x = 1 ,…,t with an integer n≥1;xn for x = 1 ,…,t and gcd (x, t) = 1 with an integer n≥1;ex for x = 1 ,…,T with an integer e, where T is the period of the sequence ex modulo t.Some of the results can be extended to composite moduli and to sums of multiplicative characters as well. Character sums with the above sequences have some cryptographic motivation and applications and have been considered in several papers by J. B. Friedlander, D. Lieman and I. E. Shparlinski. In particular several previous bounds are generalized and improved.