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CAs bet the farm on the idea that doing two separate DNS queries instead of one will keep them safe. This is a ridiculous assumption. Sophisticated attackers ca
by peterwwillis 8y ago
CAs bet the farm on the idea that doing two separate DNS queries instead of one will keep them safe. This is a ridiculous assumption. Sophisticated attackers can often successfully attack multiple targets at once.
They can use a secondary challenge, but this being optional completely defeats the purpose. A MITM attack will allow an attacker to pretend to be the target during creation of a new cert, tricking a random CA into giving them a valid cert. You do not need to use the CA that the site owners use, so their use of an extra challenge is irrelevant.
- icebraining 8y agoLots of assumptions which are ridiculous in theory are pretty good in practice. Having to MITM multiple servers just to get a cert (which will most likely be detected on the CT logs) is orders of magnitudes harder than just clicking a button on Firesheep or adding a few lines of code to a router malware. Credit cards literally rely on every single merchant not leaking their info, yet as flawed as that is, there's no great pressure to replace them.
- AstralStorm 8y agoCredit cards have manual charge back as a fallback with human driven process. The equivalent fallback for certificates does not exist. You can only revoke.
- tptacek 8y agoThey're not just doing two queries. Anybody on HN with a strong opinion about DNS and CAs and a bare minimum of programming ability could rig up a fairly sophisticated DNS validation service in under a week. Just think about how you would do it, given a pretty reasonable budget.
- peterwwillis 8y agoI'm not thinking about a sophisticated service. I'm thinking about the weakest link in the chain that I could possibly exploit to generate fake certs. Pick the least secure CA with the least secure validation method and you now have valid fake certs. Even if DNS by itself was secure enough to validate, this is a single factor and there are many ways to exploit a single factor. Why a secondary mechanism/factor isn't required for critical infrastructure makes no sense.
- tptacek 8y agoI'm not making a point about the CA system as a whole, just about multi-perspective DNS verification.
- viraptor 8y agoI didn't say they do that. Just that it's one of the ways to avoid a single, targeted mitm. There are many other approaches and cab baseline requirements (3.2.2.4.) are not very specific on what's specifically expected.