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Idea that's been floated before: TOFU plus a distributed network of people automatically sharing what cert fingerprints they encounter. Chances are high that you already hit Facebook on your $device, and if you all of a sudden retrieved a certificate that didn't match the one you had before, or that most other people online hadn't seen, halt and throw up the warnings.

Given the exploitability, laziness, general failure to follow best practices, not to mention misaligned incentives that we're seeing from major CA vendors, having centralized CAs seems like an ever-worsening solution.




Where do you store the trust from all those people to be able to query the statistics? That's just another central point of failure.


It's not as if distributed hash stores are new...


That didn't answer anything. How can you trust the result if anyone can write there. How can you trust the individual store that it doesn't manipulate its contents, etc.


And how would rollover work?


It would wind up being visible to a large chunk of users simultaneously. Furthermore, since we're relying on the wisdom of the crowd rather than a true CA, you'd be able to trust companies' own CAs rather than delegating off to a not-so-trusted third party.

In other words, if someone claiming to be Facebook has told a significant number of people all over the world that Facebook's cert fingerprint is ABCD124, and that fingerprint matches what they're getting presented, it's probably legitimate. We can add additional points for the cert signer being the same one as the previous cert, lack of listing in a CRL, cert transparency logs, etc.

There's no reason this system couldn't bolt on top of the existing CA infrastructure to avoid a bootstrapping problem either.

It adds a probability value into the mix, in other words. That value has always existed, but now we expose it to the user in some way and stop pretending that it does not.


This is what HTTP Public Key Pinning is for; the hash of the public key of the cert tells browsers to not trust a cert for the same domain with a different public key: https://news.ycombinator.com/item?id=16582534




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