THE QUANTUM INTELLIGENCER

Cloudflare has begun automatically selecting post-quantum key exchange for connections to compatible origin servers, and now reports protected traffic of some 45 billion connections per day. The new Automatic Key Exchange capability probes each origin to learn which cryptographic algorithms it supports, then selects the strongest compatible option for TLS 1.3, preferring the hybrid post-quantum algorithm X25519MLKEM768 and falling back to classical keys where necessary. The arrangement answers a structural limitation of the TLS 1.3 handshake, in which the client must send a key share before the server states its preference, a sequence that frequently ends in a retry and added latency. Cloudflare states that daily rescans and a gradual deployment have reduced the proportion of connections demanding a HelloRetryRequest from approximately 52 per cent to 3.7 per cent. The facility is enabled by default for new and existing domains whose origins support TLS 1.3; more granular controls and detection methods are said to be in development. It should be said plainly what this result is not. The capability governs one leg of the journey only, the passage from Cloudflare's edge to an origin server, and only where both ends speak TLS 1.3. It says nothing of connections that must still fall back to classical keys, a fallback that remains part of the design for origins whose probes disclose no compatible support. None of this is offered as apology. A narrow result, in the engineering sense, is one that does exactly what it claims and no more; this is such a result, and the reduction in retries already recorded is a reduction earned on the leg it controls. It establishes that a busy exchange can perform this negotiation without the penalty it once paid. It does not establish that the whole internet will follow, nor that hybrid key exchange is thereby vindicated for every handshake. Those are larger questions, for larger instruments. —Ada H. Pemberley Dispatch from The Prepared E0