No more secret certs
Under the system Laurie and Langley propose, a web browser that accessed an SSL certificate for https://mail.google.com or any other domain would automatically check the credential against an accompanying audit proof that's cryptographically tied to the publicly accessible log of valid certificates. Credentials that don't come with a corresponding proof would be summarily rejected. In the event the official log added an entry for an unauthorized certificate, the affected domain holder would be alerted immediately and could take steps to revoke it.
The system would still be vulnerable to forgeries if one of the log's maintainers colluded with the CA that issued the bogus certificate. But the fraud would require additional work on the part of the attackers and would be easily detected using the cryptographic audit logs of other maintainers.
The Google researchers said they designed the system to be compatible with browsers that don't support it. They went on to concede that the challenge of maintaining, hosting, and monitoring the logs presented “major scaling issues,” but they said “there are many web services with at least as high an uptime requirement.” And besides, the ability to distribute multiple copies of the cryptographically signed logs across the internet could lower the burden on any one maintainer.
It was only two months ago that Langley said that Convergence, an experimental project designed to remove the blind trust that internet users are currently forced to place in CAs, was too unworkable to be integrated into Google's Chrome browser. Moxie Marlinspike, the security researcher who designed the SSL alternative, said the challenge to any fix is finding agreement among the affected browser makers, website operators, CAs, and end users – and that will be no different this time.
“With all of this stuff, it's easy to come up with new ideas, and the hard part is getting them done,” Marlinspike told The Register. “At first glance, it seems this is a major undertaking in terms of getting it done. It would require every CA being complicit in changing the way they operate, as well as every browser and every webserver.” ®