Abstract: Apparati, methods, and computer readable media for enabling two parties (1,2) to exchange encrypted messages, exchange symmetric cryptographic keys, and perform functions of public key cryptography. First and second key exchange algorithms use commuting pairs of subsets of a monoid. The first key exchange algorithm has four principal embodiments. In three of the embodiments, a set of matrices over a hyperbolic ring is used as the monoid. In the fourth embodiment, a braid group is used as the monoid. The second key exchange algorithm has five principal embodiments. In four of the embodiments, a set of matrices over a hyperbolic ring is used as the monoid. In the fifth embodiment, a braid group is used as the monoid.