  A Post-Quantum Key Exchange is needed since the availability of quantum
computers that allegedly allow breaking classical algorithms like
Diffie-Hellman, El Gamal, RSA and others within a practical amount of time is
broadly assumed in literature. Although our survey suggests that practical
quantum computers appear to be by far less advanced as actually required to
break state-of-the-art key negotiation algorithms, it is of high scientific
interest to develop fundamentally immune key negotiation methods. A novel
polymorphic algorithm based on permutable functions and defined over the field
of real numbers is proposed. The proposed key exchange can operate with at
least four different strategies. The cryptosystem itself is highly variable
and, due to the fact that rounding operations are inevitable and mandatory on a
traditional computer system, decoherence of the quantum computer system would
lead to a premature end of the computation on quantum systems.
