Cultivating a robust and efficient quantum-safe HTTPS

What happened

MTCs replace the heavy, serialized chain of signatures found in traditional PKI with compact Merkle Tree proofs . To ensure the scalability and efficiency of the ecosystem, Chrome has no immediate plan to add traditional X.509 certificates containing post-quantum cryptography to the Chrome Root Store .

Instead, Chrome, in collaboration with other partners, is developing an evolution of HTTPS certificates based on Merkle Tree Certificates (MTCs), currently in development in the PLANTS working group. In this model, a Certification Authority (CA) signs a single "Tree Head" representing potentially millions of certificates, and the "certificate" sent to the browser is merely a lightweight proof of inclusion in that tree.

MTCs enable the adoption of robust post-quantum algorithms without incurring the massive bandwidth penalty of classical X.509 certificate chains. Finally, with MTCs, transparency is a fundamental property of issuance: it is impossible to issue a certificate without including it in a public tree.

Key facts

• MTCs replace the heavy, serialized chain of signatures — found: in traditional PKI with compact Merkle Tree proofs