Cloudflare Measures Origin TLS Preferences, Cutting Handshake Retries from 52% to 3.7%
Cloudflare has replaced its static X25519 guess for origin TLS handshakes with per-origin measurement. HelloRetryRequests on scanned origins fell from roughly 52% to 3.7%, removing over 150 ms from p90 latency. Post-quantum connections completing in one round trip rose from 0% to 99.2%, though only 12.8% of origins support it. By Steef-Jan Wiggers
Cloudflare has begun actively probing origins to measure their TLS preferences, which has led to a significant reduction in handshake retries. Previously, Cloudflare assumed X25519 as the key agreement algorithm for every origin, but measurements showed this guess was optimal only for about 30% of connections. By probing, Cloudflare discovered that 30% of origins preferred X25519 or X384, incurring an extra round trip for incorrect guesses.
The new ability to probe per-origin has uncovered thousands of instances where post-quantum support was never revealed passively. Cloudflare now leads with the preferred algorithm, reducing handshake latency by removing the HelloRetryRequest. This improvement has cut handshake retries from 52% to 3.7% and reduced the p90 handshake latency by over 150ms.
Written by urgent.news from InfoQ's reporting — not their text. Machine-written — may contain errors; check the original before relying on it.
