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0 pointsnly11y ago0 comments

The objective is to leverage DNSSEC to prevent downgrade attacks. Whether or not you are connecting to a host over HTTP or HTTPS you need to query DNS, which makes it an ideal place to introduce a message to clients to tell them what they should be doing. In an ideal world, a DNSSEC enabled recursive resolver, querying a domain name under a DNSSEC-enabled TLD, should not be fooled to downgrade.

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tptacek11y ago

Again: this mitigates (but probably does not decisively solve) one avenue for downgrade attacks. But downgrade attacks against HTTPS would remain possible --- trivial, in fact, without HSTS, which leaves you with the first-contact problem with or without DNSSEC.

So again: what's the point? Compared to HSTS headers, DNSSEC is incredibly expensive.

nlyOP11y ago

The point is you can have a record in DNS that says "never use HTTP" that protects clients who haven't yet seen HSTS, and you can use a TLSA-like SRV record to protect clients who haven't yet seen HPKP.

Another thing you're missing is that the CA system almost boils down to the integrity of DNS already, since you can get a CA to issue a basic certificate for a domain simply through weak ownership verification (i.e. if someone controls or MITMs your MX records/responses you're fucked).

tptacek11y ago

Once again: you can foil domain validation with or without DNSSEC by downgrading SMTP.

Why bother with DNSSEC?

You also didn't address my ECC point upthread. Today, APNIC advises DNS administrators not to use the (crappy) P-256 ECDSA DNSSEC supports, because it breaks ~1/3rd of all resolvers. That's for the ECC variant DNSSEC actually "supports".

How exactly would you propose a rollout of Ed25519 (or equivalent) crypto in DNSSEC? Or, where is the flaw in my argument?

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0 pointsnly11y ago0 comments

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tptacek11y ago

So again: what's the point? Compared to HSTS headers, DNSSEC is incredibly expensive.

nlyOP11y ago

tptacek11y ago

Once again: you can foil domain validation with or without DNSSEC by downgrading SMTP.

Why bother with DNSSEC?

How exactly would you propose a rollout of Ed25519 (or equivalent) crypto in DNSSEC? Or, where is the flaw in my argument?

1 more reply

j / k navigate · click thread line to collapse