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It is possible using a "Certification Authority Authorization" (CAA) DNS record to specify which CA is allowed to sign certs for your domain and using DNSSEC yo

It is possible using a "Certification Authority Authorization" (CAA) DNS record to specify which CA is allowed to sign certs for your domain and using DNSSEC you get a separate channel of trust. However CAA (and DNSSEC) is rarely used, so most likely the MITM-part will just block lookups.

schoen 6y ago
Also, CAA is explicitly specified to only constrain certificate issuance, not certificate acceptance. Only the issuing CA is supposed to check it, not the browser. RFC 8659: A set of CAA records describes only current grants of authority to issue certificates for the corresponding DNS domain name. Since certificates are valid for a period of time, it is possible that a certificate that is not conformant with the CAA records currently published was conformant with the CAA records published at the time that the certificate was issued. Relying Parties MUST NOT use CAA records as part of certificate validation.
Melkman 6y ago
CAA is not the record for this. As @schoen already replied, it is only used by CA's to check if they are allowed to issue a certificate to a domain. But with DANE TLSA Resource Records you can pin a public key to a website. Alas the implementation of TLSA-RR checking in browsers is dependent on extensions at this time. I wish it was native in browsers with a big red sign when violated. When done in combination with DNSSEC it's very hard to fake certificates. Or more precisely asymmetric cryptography key pairs used by servers. Certificates for TLS would not be needed anymore if TLSA-RR's were standard practice. A company might still use a certificate to attest it's identity beyond internet domain ownership. Edit: This is for TLSA 3 1 1 and 3 1 2 records. That's what I have experience with. Just read on Wikipedia a lot more is possible with TLSA-RR's including certificate and CA pinning. https://en.wikipedia.org/wiki/DNS-based_Authentication_of_Named_Entities#TLSA_RR https://en.wikipedia.org/wiki/DNS-based_Authentication_of_Na...
- tptacek 6y ago
  It's unlikely ever to be native in browsers. Native DANE code was proposed in Firefox and actually landed in Chrome, which later removed it, because it (a) didn't work reliably on the actual Internet, and (b) in fallback mode, amounts to adding just one more CA to the pile of CAs Chrome already has to trust. When a CA can be shown to have misissued a certificate, Google can (and has, as it did in the Symantec case) distrust it, nuking the CA from orbit. It has no such powers with a CA baked into the DNS; Google can't distrust .COM. People should be careful what they wish for. But not too careful in this case; DNSSEC is moribund, and unlikely to be revived.

schoen 6y ago

Also, CAA is explicitly specified to only constrain certificate issuance, not certificate acceptance. Only the issuing CA is supposed to check it, not the browser. RFC 8659: A set of CAA records describes only current grants of authority to issue certificates for the corresponding DNS domain name. Since certificates are valid for a period of time, it is possible that a certificate that is not conformant with the CAA records currently published was conformant with the CAA records published at the time that the certificate was issued. Relying Parties MUST NOT use CAA records as part of certificate validation.

Melkman 6y ago

CAA is not the record for this. As @schoen already replied, it is only used by CA's to check if they are allowed to issue a certificate to a domain. But with DANE TLSA Resource Records you can pin a public key to a website. Alas the implementation of TLSA-RR checking in browsers is dependent on extensions at this time. I wish it was native in browsers with a big red sign when violated. When done in combination with DNSSEC it's very hard to fake certificates. Or more precisely asymmetric cryptography key pairs used by servers. Certificates for TLS would not be needed anymore if TLSA-RR's were standard practice. A company might still use a certificate to attest it's identity beyond internet domain ownership. Edit: This is for TLSA 3 1 1 and 3 1 2 records. That's what I have experience with. Just read on Wikipedia a lot more is possible with TLSA-RR's including certificate and CA pinning. https://en.wikipedia.org/wiki/DNS-based_Authentication_of_Named_Entities#TLSA_RR https://en.wikipedia.org/wiki/DNS-based_Authentication_of_Na...

tptacek 6y ago
It's unlikely ever to be native in browsers. Native DANE code was proposed in Firefox and actually landed in Chrome, which later removed it, because it (a) didn't work reliably on the actual Internet, and (b) in fallback mode, amounts to adding just one more CA to the pile of CAs Chrome already has to trust. When a CA can be shown to have misissued a certificate, Google can (and has, as it did in the Symantec case) distrust it, nuking the CA from orbit. It has no such powers with a CA baked into the DNS; Google can't distrust .COM. People should be careful what they wish for. But not too careful in this case; DNSSEC is moribund, and unlikely to be revived.