Cloudflare to issue quantum-safe TLS certificates using Merkle Tree design

Cloudflare announced plans to issue quantum-safe TLS certificates starting in the first quarter of 2027, using an open-source platform that supports both classic and post-quantum certificates. The hybrid certificates will be available at no cost to all users, including both paying and non-paying Cloudflare customers.

To accelerate adoption across the web’s public key infrastructure (WebPKI), Cloudflare will acquire a trusted certificate root from GlobalSign. This acquisition is intended to enable millions of websites to adopt post-quantum certificates without additional performance overhead or infrastructure changes.

The company emphasized that the transition to quantum-resistant certificates requires fundamental architectural changes, not merely swapping algorithms. Earlier approaches that attempted to directly replace classical X.509 certificates with quantum-proof variants were found to increase handshake data by roughly 40 times, which would break compatibility with existing internet infrastructure.

Cloudflare and Google have been testing a solution based on Merkle Trees, a hierarchical data structure that uses cryptographic hashes to verify large datasets with minimal data transmission. This design reduces handshake data to about 40 kilobytes—comparable to current TLS handshakes—while enabling quantum-resistant authentication.

Under the current WebPKI system, certificate authenticity relies on a chain of quantum-vulnerable signatures. Cloudflare’s plan replaces these chains with compact Merkle Tree proofs, where a certificate authority signs a single “tree head” that can represent millions of certificates. Browsers typically receive a lightweight “landmark” proof confirming the certificate’s presence in the tree.

The company also highlighted the integration of public transparency logs into the certificate issuance process. Unlike today’s system, where logging is a separate step, Merkle Tree Certificates embed logging as a core part of issuance. This design ensures that transparency becomes a requirement for operation rather than an optional add-on, helping prevent counterfeit certificates such as those issued during the 2011 DigiNotar breach.

Cloudflare’s approach includes the use of the Automated Certificate Management Environment (ACME), an open-source protocol for automated certificate issuance and renewal. Additionally, the quantum-resistant certificates will support out-of-band signature delivery—for example, via browser updates—if technical issues prevent real-time landmark updates.