Consider NSEC in enumeration of DNSSEC-enabled domains

For finding subdomains in "holes" in the wordlist, the [NSEC extension to DNSSEC](https://en.wikipedia.org/wiki/Domain_Name_System_Security_Extensions#Operation) might be useful to look at. This can also be used to skip over words which should not be necessary to resolve, as they should be "cryptographically provably non-existent".

See [more information on Wikipedia](https://en.wikipedia.org/wiki/Domain_Name_System_Security_Extensions#Authenticating_NXDOMAIN_responses_and_NSEC), the [nsec3 walker](https://dnscurve.org/nsec3walker.html) for alternate technologies, and of course other sources.