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dnssec.py
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dnssec.py
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#!/usr/bin/env python3
#
# Electrum ABC - lightweight eCash client
# Copyright (C) 2020 The Electrum ABC developers
# Copyright (C) 2015 Thomas Voegtlin
#
# Permission is hereby granted, free of charge, to any person
# obtaining a copy of this software and associated documentation files
# (the "Software"), to deal in the Software without restriction,
# including without limitation the rights to use, copy, modify, merge,
# publish, distribute, sublicense, and/or sell copies of the Software,
# and to permit persons to whom the Software is furnished to do so,
# subject to the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS
# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
# ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN
# CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
# SOFTWARE.
# Check DNSSEC trust chain.
# Todo: verify expiration dates
#
# Based on
# http://backreference.org/2010/11/17/dnssec-verification-with-dig/
# https://github.com/rthalley/dnspython/blob/master/tests/test_dnssec.py
import dns.dnssec
import dns.message
import dns.name
import dns.query
import dns.rdatatype
import dns.rdtypes.ANY.CNAME
import dns.rdtypes.ANY.DLV
import dns.rdtypes.ANY.DNSKEY
import dns.rdtypes.ANY.DS
import dns.rdtypes.ANY.NS
import dns.rdtypes.ANY.NSEC
import dns.rdtypes.ANY.NSEC3
import dns.rdtypes.ANY.NSEC3PARAM
import dns.rdtypes.ANY.RRSIG
import dns.rdtypes.ANY.SOA
import dns.rdtypes.ANY.TXT
import dns.rdtypes.IN.A
import dns.rdtypes.IN.AAAA
import dns.resolver
from .printerror import print_error
# hard-coded trust anchors (root KSKs)
trust_anchors = [
# KSK-2017:
dns.rrset.from_text(
".",
1,
"IN",
"DNSKEY",
"257 3 8"
" AwEAAaz/tAm8yTn4Mfeh5eyI96WSVexTBAvkMgJzkKTOiW1vkIbzxeF3+/4RgWOq7HrxRixHlFlExOLAJr5emLvN7SWXgnLh4+B5xQlNVz8Og8kvArMtNROxVQuCaSnIDdD5LKyWbRd2n9WGe2R8PzgCmr3EgVLrjyBxWezF0jLHwVN8efS3rCj/EWgvIWgb9tarpVUDK/b58Da+sqqls3eNbuv7pr+eoZG+SrDK6nWeL3c6H5Apxz7LjVc1uTIdsIXxuOLYA4/ilBmSVIzuDWfdRUfhHdY6+cn8HFRm+2hM8AnXGXws9555KrUB5qihylGa8subX2Nn6UwNR1AkUTV74bU=",
),
# KSK-2010:
dns.rrset.from_text(
".",
15202,
"IN",
"DNSKEY",
"257 3 8 AwEAAagAIKlVZrpC6Ia7gEzahOR+9W29euxhJhVVLOyQbSEW0O8gcCjF"
" FVQUTf6v58fLjwBd0YI0EzrAcQqBGCzh/RStIoO8g0NfnfL2MTJRkxoX"
" bfDaUeVPQuYEhg37NZWAJQ9VnMVDxP/VHL496M/QZxkjf5/Efucp2gaD"
" X6RS6CXpoY68LsvPVjR0ZSwzz1apAzvN9dlzEheX7ICJBBtuA6G3LQpz"
" W5hOA2hzCTMjJPJ8LbqF6dsV6DoBQzgul0sGIcGOYl7OyQdXfZ57relS"
" Qageu+ipAdTTJ25AsRTAoub8ONGcLmqrAmRLKBP1dfwhYB4N7knNnulq QxA+Uk1ihz0=",
),
]
def check_query(ns, sub, _type, keys):
q = dns.message.make_query(sub, _type, want_dnssec=True)
response = dns.query.tcp(q, ns, timeout=5)
assert response.rcode() == 0, "No answer"
answer = response.answer
assert len(answer) != 0, ("No DNS record found", sub, _type)
assert len(answer) != 1, ("No DNSSEC record found", sub, _type)
if answer[0].rdtype == dns.rdatatype.RRSIG:
rrsig, rrset = answer
elif answer[1].rdtype == dns.rdatatype.RRSIG:
rrset, rrsig = answer
else:
raise RuntimeError("No signature set in record")
if keys is None:
keys = {dns.name.from_text(sub): rrset}
dns.dnssec.validate(rrset, rrsig, keys)
return rrset
def get_and_validate(ns, url, _type):
# get trusted root key
root_rrset = None
for dnskey_rr in trust_anchors:
try:
# Check if there is a valid signature for the root dnskey
root_rrset = check_query(
ns, "", dns.rdatatype.DNSKEY, {dns.name.root: dnskey_rr}
)
break
except dns.dnssec.ValidationFailure:
# It's OK as long as one key validates
continue
if not root_rrset:
raise dns.dnssec.ValidationFailure("None of the trust anchors found in DNS")
keys = {dns.name.root: root_rrset}
# top-down verification
parts = url.split(".")
for i in range(len(parts), 0, -1):
sub = ".".join(parts[i - 1 :])
name = dns.name.from_text(sub)
# If server is authoritative, don't fetch DNSKEY
query = dns.message.make_query(sub, dns.rdatatype.NS)
response = dns.query.udp(query, ns, 3)
assert response.rcode() == dns.rcode.NOERROR, "query error"
rrset = (
response.authority[0] if len(response.authority) > 0 else response.answer[0]
)
rr = rrset[0]
if rr.rdtype == dns.rdatatype.SOA:
continue
# get DNSKEY (self-signed)
rrset = check_query(ns, sub, dns.rdatatype.DNSKEY, None)
# get DS (signed by parent)
ds_rrset = check_query(ns, sub, dns.rdatatype.DS, keys)
# verify that a signed DS validates DNSKEY
for ds in ds_rrset:
for dnskey in rrset:
htype = "SHA256" if ds.digest_type == 2 else "SHA1"
good_ds = dns.dnssec.make_ds(name, dnskey, htype)
if ds == good_ds:
break
else:
continue
break
else:
raise RuntimeError("DS does not match DNSKEY")
# set key for next iteration
keys = {name: rrset}
# get TXT record (signed by zone)
rrset = check_query(ns, url, _type, keys)
return rrset
def query(url, rtype):
# 8.8.8.8 is Google's public DNS server
nameservers = ["8.8.8.8"]
ns = nameservers[0]
try:
out = get_and_validate(ns, url, rtype)
validated = True
except Exception as e:
# traceback.print_exc(file=sys.stderr)
print_error("DNSSEC error:", str(e))
resolver = dns.resolver.get_default_resolver()
out = resolver.query(url, rtype)
validated = False
return out, validated