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shincert's comments

shincert | 8 years ago | on: Ask HN: Secure DNS resolution in a system

> Basically, unless everything is 100% DNSSEC, there's an opportunity for tampering. Fortunately, though, OCSP responses are signed, as we mentioned earlier. If the OCSP response comes with a valid signature, it can be trusted -- whether DNSSEC is in use or not. A response with an invalid signature (for whatever reason) obviously cannot be trusted. Let me ask you that first question again with this in mind: will running your own DNS server increase the security any? Will it increase the amount of trust you have in the validity of the certificates presented to you by clients?

That was very enlightening, thank you for your help.

I can see it won't improve my trust on the OCSP responses or CRLs, but would it not be desirable to encrypt as much traffic (i.e. DNS queries) as I can in an effort to prohibit a potential attacker from employing traffic analysis techniques with the goal to learn something? This hypothetical scenario doesn't seem so farfetched to me.

Eventually, my encrypted DNS query will be forwarded to a DNS resolver that doesn't employ encryption and it will be in the clear, but how would the attacker know where to look next? If the original DNS query is encrypted, an attacker sniffing the network will not be able to know which DNS resolver the query was forwarded to, right? If so then he can't follow up on that and I've successfully disabled it from learning what the DNS query was about.

In short, I am not trying to increase my trust in the exchanges, but rather hide them as much as possible for the sake of obscurity. Is this reasonable?

shincert | 8 years ago | on: Ask HN: Secure DNS resolution in a system

> Assuming the RRs for the domains you are querying are signed, that's (IMO) probably all you need to do. While OCSP happens over plain-text HTTP, the responses are also signed so that you can verify them.

I will make sure that's the case. What I didn't explain yet is that I am doing this for a university project and I am fishing for extra points. So I was trying to justify running my own DNS server. Is it reasonable?

> I don't think there's much more you can really do (as the DNS queries/responses will travel over the Internet "in the clear" -- and, thus, subject to tampering/modification).

I really should have done more research on this, but I imagined I could encrypt the DNS queries themselves and forward them to a public recursive DNS server. Could I not use DNSCRYPT or DNS-over-TLS for this purpose?

> Also, an attacker could block your HTTP requests (for CRL downloads/OCSP queries). How does your application react when it doesn't get a response? "Fail open" or "fail closed"?

Assuming the server has at least downloaded an initial CRL, I could always fallback to that. I haven't played much with this yet, but I think that's the big advantage of a CRL versus an OCSP query, no?

I guess I should "fail closed" to cover all holes but then I'm basically letting the attacker DoS the server. What is best?

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