Cloudflare Research: Post-Quantum Key Agreement

On essentially all domains served (1) through Cloudflare, including this one, we have enabled hybrid post-quantum key agreement. We are also rolling out support for post-quantum key agreement for connection from Cloudflare to origins (3). Check out our blog post the state of the post-quantum Internet for more context.

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Deployed key agreements

Available with TLSv1.3 including HTTP/3 (QUIC)

Default for Chrome 124-130 on Desktop. For older Chrome or on Mobile, you need to toggle TLS 1.3 hybridized Kyber support (enable-tls13-kyber) in chrome://flags.
Default for Edge 124+.
Default for recent Opera and Brave.
Firefox 124+ if you turn on security.tls.enable_kyber in about:config. Firefox 128+ and network.http.http3.enable_kyber for QUIC/HTTP3.
Our fork of Go.
Default for Go 1.23. [new!]
BoringSSL.
Our fork of QUIC-go.
Goutam Tamvada's fork of Firefox.
Open Quantum Safe C library.
Zig 0.11.0+
nginx when compiled with BoringSSL (guide).
Caddy HTTP server nightly compiled with Go 1.23+.
Botan C++ library 3.2.0+ (instructions)
ISRG's fork of Rustls [new!]

The state of the post-quantum Internet (early 2024)
tldr.fail explains how large post-quantum ClientHello could break buggy software.

You can reach us directly at ask-research@cloudflare.com with questions and feedback.