Cloudflare says it will begin issuing quantum-resistant TLS certificates in the first quarter of 2027, in what the company describes as a fundamental overhaul of how the web proves a site's identity.
The plan replaces today's WebPKI signature chains with Merkle Tree Certificates. Under the current system a browser validates a multi-link chain of signatures that a sufficiently powerful quantum computer running Shor's algorithm could eventually forge — along with the public keys of certificate transparency logs and the signed timestamps that prove a certificate was registered. Swapping every signature for a post-quantum one is considered resource-prohibitive because the signatures are much larger and the chain is long.
In the Merkle design, first announced by Google in February and since tested by both companies in limited pilots, a certificate authority signs only a single "tree head" that can stand for millions of certificates. Most of the time a browser receives a "landmark", a lightweight proof that the certificate is located somewhere in the tree. Cloudflare says this keeps the handshake data at about 40 kilobytes, roughly what browsers process now.
The approach also folds transparency logging into issuance itself. Today the append-only public logs — introduced industry-wide after the 2011 DigiNotar breach, in which 500 counterfeit certificates were minted for Google and other sites — are a separate process. "By coupling issuance and logging, transparency becomes a requirement for operation, rather than an add-on," Cloudflare engineer Mari Galicer said.
Cloudflare also points to supporting pieces of the plan: the Automated Certificate Management Environment (ACME) for continuous renewal, and an out-of-band mechanism to deliver a signature through, for example, a browser update if a server cannot supply a fresh landmark. The company has not yet published a migration date for the wider ecosystem, and browsers, operating systems and other certificate authorities would all have to follow for the change to take effect in practice.
