Cloudflare plans to issue quantum-safe TLS certificates

Cloudflare said Tuesday it plans to issue quantum-proof TLS certificates, becoming one of the first certificate authorities to offer certificates built on cryptography widely believed to withstand attacks from quantum computers.

The Internet infrastructure provider said it will use an open-source platform that issues both classic TLS certificates and a post-quantum equivalent known as Merkle Tree Certificates. The hybrid certificates will be free to paying and non-paying users alike. To build the massive system and reach across the sprawling TLS ecosystem, Cloudflare has signed a definitive agreement to acquire an established, broadly trusted root from CA GlobalSign.

Why a new architecture is needed

Safeguarding the web's public key infrastructure (WebPKI) against quantum attacks requires fundamental architectural changes rather than a simple algorithm swap. Quantum-proof versions of today's X.509 certificates would add roughly 40 times the data required for a TLS handshake, the exchange that occurs each time a browser establishes a session with a server. The added computation and bandwidth would break the Internet as we know it.

Merkle Tree Certificates

In February, Google proposed a solution: Merkle Trees, hierarchical data structures that use cryptographic hashes to verify large amounts of information from a small fraction of their contents. The design, which Google and Cloudflare have been testing in limited pilot programs, cuts handshake data to about 40 kilobytes, roughly what is processed today.

Today's WebPKI proves a certificate's authenticity with a multi-link chain of quantum-vulnerable signatures. Merkle Tree Certificates replace that chain with a compact proof: a certificate authority signs a single "tree head" representing millions of certificates, and a browser usually handles a "landmark," a lightweight proof of a certificate's position in the tree. Logging also becomes part of issuance rather than a separate process. "By coupling issuance and logging, transparency becomes a requirement for operation, rather than an add-on," Cloudflare engineer Mari Galicer said.

Timeline and transparency

Cloudflare has applied for inclusion in the Chrome, Apple, Microsoft and Mozilla root programs, aiming at Chrome's quantum-resistant root program. Steve Goldsmith wrote that the company is not issuing certificates yet and that it is committing to the work in public, sharing the milestones as they land. Cloudflare expects to start issuing certificates in the first quarter of 2027, promising ACME-first issuance and mandatory renewal automation.