Beyond Post-quantum Stereotypes

The talk opens with a refresher on classical secure communication. Two parties use asymmetric cryptography to agree on a shared key over an untrusted network, then switch to symmetric encryption for the traffic. Certificates from a trusted authority guard against a man-in-the-middle, and security is measured by the work an attacker needs to forge or decrypt data.

The middle section covers the quantum threat. Shor's algorithm would break the factoring and discrete logarithm problems behind RSA, ECDH and ECDSA, while Grover's algorithm weakens symmetric keys, so AES-128 falls short and AES-256 remains acceptable. The speakers describe the lattice and hash-based schemes standardised by NIST, stress that they run on ordinary hardware, and explain hybrid designs that pair a classical and a post-quantum algorithm so both must be broken. They also outline the store-now, decrypt-later risk for recorded traffic and the forged-signature risk for certificates.

The closing part is practical. Organizations should inventory where cryptography is used, since many browsers, CDNs, reverse proxies and recent OpenSSH releases already negotiate hybrid key exchange, while some Windows services and VPNs lag behind. For auditors, post-quantum implementations are still classical software: check conformance to standards and test vectors, random number generation, key handling, and side channels such as timing and cache leakage.