Google on Friday unveiled its plan for its Chrome browser to secure HTTPS certificates against quantum computer attacks without breaking the Internet.
The objective is a tall order. The quantum-resistant cryptographic data needed to transparently publish TLS certificates is roughly 40 times bigger than the classical cryptographic material used today. Today’s X.509 certificates are about 64 bytes in size, and comprise six elliptic curve signatures and two EC public keys. This material can be cracked through the quantum-enabled Shor’s algorithm. Certificates containing the equivalent quantum-resistant cryptographic material are roughly 2.5 kilobytes. All this data must be transmitted when a browser connects to a site.
The bigger they come, the slower they move
“The bigger you make the certificate, the slower the handshake and the more people you leave behind,” said Bas Westerbaan, principal research engineer at Cloudflare, which is partnering with Google on the transition. “Our problem is we don’t want to leave people behind in this transition.” Speaking to Ars, he said that people will likely disable the new encryption if it slows their browsing. He added that the massive size increase can also degrade “middle boxes,” which sit between browsers and the final site.
To bypass the bottleneck, companies are turning to Merkle Trees, a data structure that uses cryptographic hashes and other math to verify the contents of large amounts of information using a small fraction of material used in more traditional verification processes in public key infrastructure.
Merkle Tree Certificates, “replace the heavy, serialized chain of signatures found in traditional PKI with compact Merkle Tree proofs,” members of Google’s Chrome Secure Web and Networking Team wrote Friday. “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.”