Post-quantum readiness for TLS at Meta

This post details Meta's migration to post-quantum cryptography (PQC) for TLS, specifically focusing on hybrid key exchange using Kyber with X25519. It highlights the challenges encountered, including large packet sizes impacting TLS resumption and TCP Fast Open, leading to the use of Kyber512 for certain internal communications to maintain performance. A multithreading race condition in the liboqs library was identified and fixed. The post also discusses cross-domain resumption handshake thrash and the strategies employed to mitigate it. The technical contributions include the implementation of hybrid key exchange in Fizz, the use of liboqs, and the analysis and resolution of specific performance and stability issues related to PQC deployment at scale.