python - Programmatically check if domains are DNSSEC protected

Question

As the title says I want to programmatically check if a DNS response for a domain are protected with DNSSEC.
How could I do this?

It would be great, if there is a pythonic solution for this.

UPDATE: changed request to response, sorry for the confusion

Answer 1

Using a DNS resolver (e.g. dnspython), you can query the domain for its DNSKEY RRset and turn on the DO (dnssec OK) query flag. If the query succeeds, the answer will have the AD (authenticated data) flag set and will contain the RRSIG signatures for the zone (if it is signed).

Update: a basic example using dnspython

import dns.name
import dns.query
import dns.dnssec
import dns.message
import dns.resolver
import dns.rdatatype

# get nameservers for target domain
response = dns.resolver.query('example.com.',dns.rdatatype.NS)

# we'll use the first nameserver in this example
nsname = response.rrset[0].to_text() # name
response = dns.resolver.query(nsname,dns.rdatatype.A)
nsaddr = response.rrset[0].to_text() # IPv4

# get DNSKEY for zone
request = dns.message.make_query('example.com.',
                                 dns.rdatatype.DNSKEY,
                                 want_dnssec=True)

# send the query
response = dns.query.udp(request,nsaddr)
if response.rcode() != 0:
    # HANDLE QUERY FAILED (SERVER ERROR OR NO DNSKEY RECORD)

# answer should contain two RRSET: DNSKEY and RRSIG(DNSKEY)
answer = response.answer
if len(answer) != 2:
    # SOMETHING WENT WRONG

# the DNSKEY should be self signed, validate it
name = dns.name.from_text('example.com.')
try:
    dns.dnssec.validate(answer[0],answer[1],{name:answer[0]})
except dns.dnssec.ValidationFailure:
    # BE SUSPICIOUS
else:
    # WE'RE GOOD, THERE'S A VALID DNSSEC SELF-SIGNED KEY FOR example.com