Post-Quantum Cryptography: Preparing for Q-Day

Quantum computers pose a real threat to many cryptographic systems today. Algorithms such as RSA and ECC may eventually be broken within a short amount of time — a scenario often referred to as “Q-Day.” However, there is no need for panic. With post-quantum cryptography (PQC), standardized and quantum-resistant algorithms are already emerging. In particular, algorithms like CRYSTALS-Kyber, which are part of the latest NIST standards, are increasingly being adopted in browsers, servers, and modern protocols such as TLS and QUIC. In this talk, I provide an accessible introduction to the foundations of quantum mechanics relevant to cryptography and explain why quantum computers threaten classical cryptographic algorithms. We take a deeper look at what Q-Day actually means in practice and how organizations can start preparing today. Beyond the fundamentals, the talk offers a deeper technical insight into lattice-based cryptography, including the mathematical principles behind CRYSTALS-Kyber and other modern post-quantum algorithms. Using hands-on examples with OpenSSL, NGINX, and hybrid TLS configurations, I demonstrate how existing web applications can be gradually adapted for the post-quantum era.