Abstract: Cryptographic techniques are disclosed which employ at least a five-pass protocol (5PP) for a cryptographic exchange of a secret data matrix between two computer systems. This 5PP approach improves the functioning of the computer systems by making their encrypted communications more resistant to potential quantum computing-based attacks while still resisting brute-force attacks by eavesdroppers. For example, the 5PP approach can be used to improve public-key cryptography. The system may comprise a first computer system and a second computer system, where a secret data matrix is known by the first computer system but is not shared with the second computer system in unobscured form.