# Counting points on genus-3 hyperelliptic curves with explicit real multiplication

We propose a Las Vegas probabilistic algorithm to compute the zeta function of a genus-3 hyperelliptic curve defined over a finite field F_q, with explicit real multiplication by an order Z[η] in a totally real cubic field. Our main result states that this algorithm requires an expected number of O(( q)^6) bit-operations, where the constant in the O() depends on the ring Z[η] and on the degrees of polynomials representing the endomorphism η. As a proof-of-concept, we compute the zeta function of a curve defined over a 64-bit prime field, with explicit real multiplication by Z[2cos(2π/7)].

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