Chrome Root Store

Merkle Tree Certificates Proposed to Enable Lightweight Post-Quantum HTTPS in Chrome

Google Chrome developers, together with industry partners and the IETF PLANTS working group, are introducing Merkle Tree Certificates (MTC) as the first HTTPS change designed to address performance challenges of post-quantum cryptography. The new format replaces parts of traditional X.509 certificate chains with compact inclusion proofs inside a Merkle tree whose root is signed by a certificate authority. This approach significantly reduces the size of authentication data exchanged during TLS handshakes while preserving strong post-quantum security properties. MTC also enforces Certificate Transparency by design, making it impossible to issue a public certificate without recording it in a publicly verifiable log. Performance evaluations are currently underway with Cloudflare, and initial public MTC logs operated by experienced CT log providers are planned for early 2027. A dedicated post-quantum Chrome Root Store supporting only MTC is scheduled for the third quarter of 2027 and will run in parallel with the existing root store.