Hecke operators with odd determinant and binary frameproof codes beyond the probabilistic bound?

Abstract

We give a slight improvement on Xing's lower bound for frameproof codes constructed from algebraic curves. Combined with some additional number-theoretic assumptions (still conjectural) and a concatenation process, this should lead to the existence of a family of binary 2-frameproof codes of asymptotic rate going beyond the up to now best known (non-constructive) lower bound.