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0 pointstom13371mo ago0 comments

> DNSSEC actually makes DNS more decentralized: without DNSSEC, the only way to guarantee a trustworthy response is to directly ask the authoritative nameservers. But with DNSSEC, you can query third-party caching resolvers and still be able to trust the response because only a legitimate answer will have a valid signature.

but how would one verify the signature if the DNSKEY expired and you cannot fetch a fresh one because the organisation providing those keys is down? As far as I understood the TTL for those keys is different and for DENIC it seems to be 1h [0]. So if they are down for more than an hour and all RRSIG caches expire, DNS zones which have a higher TTL than 1h but use DNSSEC would also be down?

[0] dig RRSIG de. @8.8.8.8

de. 3600 IN RRSIG DNSKEY 8 1 3600 20260519214514 20260505201514 26755 de. [...]

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3 comments · 1 top-level

gucci-on-fleek1mo ago· 2 in thread

> but how would one verify the signature if the DNSKEY expired and you cannot fetch a fresh one because the organisation providing those keys is down?

In theory, this shouldn't happen, because if you use the same TTLs for your DNSSEC records and your "regular" records, then if the regular records are present in the cache, the DNSSEC records will be too.

> So if they are down for more than an hour and all RRSIG caches expire, DNS zones which have a higher TTL than 1h but use DNSSEC would also be down?

Yes, but I'd argue that the DNSSEC records should have the same TTLs for exactly this reason. That's how my domain is set up at least:

  $ dig +nocmd +nocomments +nostats +dnssec @any.ca-servers.ca. maxchernoff.ca. DS
  ;maxchernoff.ca.                        IN      DS
  maxchernoff.ca.         86400   IN      DS      62673 15 2 487B95FEFF04265826F037C9DB2E1F14FF9ADBF2C7BE246A2B9F9BFD 481BE928
  maxchernoff.ca.         86400   IN      RRSIG   DS 13 2 86400 20260512131336 20260505104433 46762 ca. ppc9LrWniPWdAI2Xq1g3FrYJGQVYayA5TtgFRkJfqOqNfe6zu/n0gwti IO3c9pOoUpIum5gPB6GLOGbGU+sfhg==
  
  $ dig +nocmd +nocomments +nostats +dnssec @ns.maxchernoff.ca. maxchernoff.ca. DNSKEY
  ;maxchernoff.ca.                        IN      DNSKEY
  maxchernoff.ca.         86400   IN      DNSKEY  257 3 15 DYs9mPDMRx/hQ9R9iGLi1Ysx1eFdhlXeCujY6PqJWeU=
  maxchernoff.ca.         86400   IN      RRSIG   DNSKEY 15 2 86400 20260518072823 20260504055823 62673 maxchernoff.ca. RgPyEvB/kjXIvoidRNF/hfm7utzDs0kxXn4qJL17TUAVYOdbLl0Vd8zt E52bGBBFv2TNEnf9O9LkiT2GBH0jAA==
  
  $ dig +nocmd +nocomments +nostats +dnssec @ns.maxchernoff.ca. maxchernoff.ca. A
  ;maxchernoff.ca.                        IN      A
  maxchernoff.ca.         86400   IN      A       152.53.36.213
  maxchernoff.ca.         86400   IN      RRSIG   A 15 2 86400 20260518072823 20260504055823 62673 maxchernoff.ca. bRfTVHnMjCFRaIh5uc0aT1vD4yh1UZrqOZDRunLbxFI1eth6nNlTiOOC xti7axVoXwB6VAoHOAnW0nL0eeJNDQ==

tom1337OP1mo ago

Thanks for explaining. I thought that once any key in the chain-of-trust of any domains DNSSEC expired the whole record went stale but turns out that was a wrong assumption. If the DNSKEY and the other records have the same TTL and the DNSSEC verification is also "cached" then that makes a lot more sense.

gucci-on-fleek1mo ago

> I thought that once any key in the chain-of-trust of any domains DNSSEC expired the whole record went stale but turns out that was a wrong assumption.

No, that actually is true, but I think (?) that the part that you were missing is that DNSSEC records are mostly the same as any other record, so they can be cached the same way. And since most resolvers are DNSSEC-enabled these days, they'll tend to request (and therefore cache) the DNSSEC records at the same time as the regular records.

There are tons of edge cases here, but it should hopefully be pretty rare for a cache to have a current A/AAAA record and stale/missing DNSSEC records.

> the DNSSEC verification is also "cached"

Technically the verification itself isn't cached, but since verification only depends on the chain of DNSSEC records, and those records are cached, it has the same effect.

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