Ciena University of Applied Sciences Bonn-Rhein-Sieg Entrust Nokia Zscaler The anticipated emergence of cryptographically relevant quantum computers (CRQCs) poses a threat to the authentication mechanisms used in TLS 1.3. This document defines a hybrid authentication mechanism that uses two independent certificates, one traditional and one post-quantum, ensuring that an attacker must break both algorithms to compromise a TLS connection. The two certificate chains are carried in a single Certificate message and two independent signatures are encoded in the CertificateVerify message.