Google and other browser makers require that all TLS certificates be published to public transparency logs, which are append-only distributed ledgers. Website owners can check the logs in real time to ensure that no fake certificates have been issued for the domains they use. The transparency programs were implemented in response to the 2011 hack of Netherlands-based DigiNotar, which allowed the creation of 500 fake certificates for Google and other websites, some of which were used to spy on web users in Iran.
Once feasible, Shor’s algorithm could be used to create classical encryption signatures and break the classical encryption public key of the certificate log. Ultimately, an attacker can use a forged signed certificate timestamp to trick a browser or operating system into believing that a certificate has been registered when it has not.
To rule out this possibility, Google is adding cryptographic content from quantum-resistant algorithms like ML-DSA. This addition would allow forgery only if an attacker breaks both classical and post-quantum encryption. The new arrangement is part of what Google is calling a quantum-resistant root store, which will complement the company’s Chrome root store, set to be formed in 2022.
MTCs use Merkle Trees to provide quantum-resistant assurance that a certificate has been published without adding at most long keys and hashes. Westerbaan said that using other techniques to reduce data size, MTCs would be approximately the same 64-byte length they are now.
The new system has already been implemented in Chrome. Currently, Cloudflare is enrolling approximately 1,000 TLS certificates to test how well the MTC works. For now, Cloudflare is building out the distributed ledger. The plan is for CAs to eventually take on that role. The Internet Engineering Task Force standards body recently formed a working group called PKI, Logs, and Tree Signatures, which is coordinating with other key players to develop long-term solutions.
“We see the adoption of MTC and quantum-resistant root stores as an important opportunity to ensure the strength of the foundation of the ecosystem today,” Google’s Friday blog post said. “By designing for the specific demands of the modern, agile Internet, we can accelerate the adoption of post-quantum resilience for all web users.”
<a href