Google Chrome Introduces Merkle Tree Certificates to Enable Quantum-Safe HTTPS

Google announced a new Chrome program to make HTTPS certificate authentication resilient to future quantum attacks by evolving Certificate Transparency (CT) toward Merkle Tree Certificates (MTCs). The approach is designed to mitigate the risk that a sufficiently capable quantum computer running Shor’s algorithm could forge classical signatures used in today’s PKI/CT ecosystem (e.g., forging Signed Certificate Timestamps to make unlogged certificates appear valid). Rather than immediately adding post-quantum X.509 certificate chains into the Chrome Root Store, Google is pursuing MTCs through the IETF’s new PLANTS working group (PKI, Logs, And Tree Signatures), replacing heavyweight serialized signature chains with compact Merkle proofs of inclusion anchored by a CA-signed tree head.

Google’s design combines classical and post-quantum cryptography (including ML-DSA) so an attacker would need to break both to successfully forge proofs, while keeping handshake/CT authentication data small. Ars Technica reports Google is using “clever math” to keep MTC-related authentication artifacts roughly 64 bytes (similar to current CT proofs) despite post-quantum key and signature size growth, and that the system is already implemented in Chrome with Cloudflare enrolling roughly 1,000 TLS certificates to test MTC behavior; Cloudflare is currently generating the distributed ledger, with a plan for CAs to eventually assume that role.