3

In my security class with David Wagner, we talked about some of the reasons why DNSSEC is not widely adopted right now. One of the reasons was that for backward compatibility reasons, clients need to accept both signed DNS records and unsigned ones. This means that websites have little incentive to start supporting DNSSEC, as a MITM can spoof a DNS record simply by not including a signature.

It seems that an easy solution to this would be to provide signed statements that a website does not currently support DNSSEC, similar to the way signed negative responses work for subdomains.

Is this a part of DNSSEC, and if not, why not? What other solutions are there to this problem / is it a problem?

  • Something like that does exist. I haven't yet tried to fully understand the details, but I can tell you where to find one relevant part of the spec: tools.ietf.org/html/rfc5155#section-6 – kasperd Feb 3 '15 at 23:46
2

This means that websites have little incentive to start supporting DNSSEC, as a MITM can spoof a DNS record simply by not including a signature.

This is incorrect. If a MITM attacker sends a result without a signature to a client that supports DNSSEC, the resolve will fail. This is because there is a signed DS record for that domain returned by the TLD's nameservers. The MITM attacker cannot also strip that record, as (s)he will then need to provide a response will a valid signed NSEC/NSEC3 record proving that the requested DS record doesn't exist. This is impossible without obtaining the TLD's (or root's) private key.

It seems that an easy solution to this would be to provide signed statements that a website does not currently support DNSSEC, similar to the way signed negative responses work for subdomains.

Is this a part of DNSSEC, and if not, why not? What other solutions are there to this problem / is it a problem?

There is no specific record responsible for domains that don't support DNSSEC. Instead, the server will prove that the DS record (which indicates the domain uses DNSSEC) doesn't exist.

One of the reasons was that for backward compatibility reasons

The EDNS specification is fully backwards compatible. As DNSSEC uses EDNS, it is also fully backwards compatible. Clients that don't support DNSSEC simply won't request (and the server won't respond with) DNSSEC signatures. These clients will not receive the benefits of DNSSEC, but will be able to query DNSSEC signed zones with no problems. The use of DS records on the root nameservers and the TLD nameservers allows for TLDs and domains to not be signed without any issues (However, such TLDs/domains will obviously not receive the benefits of DNSSEC).

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.