DEVOURED
Automatic Key Exchange: faster, post-quantum secure origin handshakes for 45 billion daily connections (and counting)
Cloudflare is now proactively probing origin servers to determine supported encryption algorithms, cutting TLS handshake latency by 150 ms at p90.
What: The new 'Automatic Key Exchange' feature replaces static guesses with active measurements of an origin server's capabilities, allowing for post-quantum hybrid (X25519MLKEM768) handshakes on the first packet.
Why it matters: Proactive capability discovery is replacing the standard TLS 1.3 'retry' mechanism to make the internet faster while simultaneously accelerating the adoption of post-quantum cryptography.
Takeaway: Check your origin server's post-quantum support using the Cloudflare Radar tool; if your server supports X25519MLKEM768, ensure your TLS middleboxes are configured to pass it through.
Deep dive
- Cloudflare previously used a static guess (X25519) for initial TLS handshakes, which forced a HelloRetryRequest (HRR) for any origin preferring other curves.
- The new system actively probes origins to map supported key agreement algorithms.
- Automatic Key Exchange is enabled by default for all Cloudflare-proxied domains.
- HRR rates dropped from 52% to 3.7% following the rollout.
- The system prefers post-quantum hybrid X25519MLKEM768 where supported.
- It enables per-subdomain granular security preferences.
- Automatic daily rescans detect changes in server configurations.
Decoder
- HelloRetryRequest (HRR): A TLS 1.3 message sent by a server to a client to request a different key agreement algorithm when the initial choice is unsupported or undesirable.
- Post-quantum hybrid: A cryptographic scheme combining a classical algorithm (like X25519) with a post-quantum algorithm (like ML-KEM) to provide security against both current and future quantum computer-based attacks.
- P90: A performance metric representing the 90th percentile of data, meaning 90% of requests perform better than this number.
- Q-Day: The hypothetical future date when quantum computers become powerful enough to break current asymmetric encryption standards.
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