<p>The paper proposes a cryptosystem for information exchange between subscribers that leverages surjective mappings of finite associative commutative rings with unity, along with systems of linear congruences over these rings. The authors present algorithms for constructing surjective mappings of rings, as well as the exchange protocol and the computational features of the protocol’s implementation tools. The system is designed to avoid cumbersome calculations and the need to construct ring operation tables. Its security relies on the combinatorial complexity associated with the set of surjective mappings and isomorphisms between finite rings of relatively small orders. Algorithms for solving systems of linear congruences, used in the exchange protocol, are applied for message encryption and have polynomial complexity. The operation of the cryptosystem is illustrated with examples.</p>