dnssec.py

#!/usr/bin/env python
#
# Electrum - lightweight Bitcoin client
# Copyright (C) 2015 Thomas Voegtlin
#
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# obtaining a copy of this software and associated documentation files
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# BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN
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# 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 traceback
# import sys
import time
import struct


import dns.name
import dns.query
import dns.dnssec
import dns.message
import dns.resolver
import dns.rdatatype
import dns.rdtypes.ANY.NS
import dns.rdtypes.ANY.CNAME
import dns.rdtypes.ANY.DLV
import dns.rdtypes.ANY.DNSKEY
import dns.rdtypes.ANY.DS
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


# Pure-Python version of dns.dnssec._validate_rsig
import ecdsa
from . import rsakey


def python_validate_rrsig(rrset, rrsig, keys, origin=None, now=None):
    from dns.dnssec import ValidationFailure, ECDSAP256SHA256, ECDSAP384SHA384
    from dns.dnssec import _find_candidate_keys, _make_hash, _is_ecdsa, _is_rsa, _to_rdata, _make_algorithm_id

    if isinstance(origin, str):
        origin = dns.name.from_text(origin, dns.name.root)

    for candidate_key in _find_candidate_keys(keys, rrsig):
        if not candidate_key:
            raise ValidationFailure('unknown key')

        # For convenience, allow the rrset to be specified as a (name, rdataset)
        # tuple as well as a proper rrset
        if isinstance(rrset, tuple):
            rrname = rrset[0]
            rdataset = rrset[1]
        else:
            rrname = rrset.name
            rdataset = rrset

        if now is None:
            now = time.time()
        if rrsig.expiration < now:
            raise ValidationFailure('expired')
        if rrsig.inception > now:
            raise ValidationFailure('not yet valid')

        hash = _make_hash(rrsig.algorithm)

        if _is_rsa(rrsig.algorithm):
            keyptr = candidate_key.key
            (bytes,) = struct.unpack('!B', keyptr[0:1])
            keyptr = keyptr[1:]
            if bytes == 0:
                (bytes,) = struct.unpack('!H', keyptr[0:2])
                keyptr = keyptr[2:]
            rsa_e = keyptr[0:bytes]
            rsa_n = keyptr[bytes:]
            n = ecdsa.util.string_to_number(rsa_n)
            e = ecdsa.util.string_to_number(rsa_e)
            pubkey = rsakey.RSAKey(n, e)
            sig = rrsig.signature

        elif _is_ecdsa(rrsig.algorithm):
            if rrsig.algorithm == ECDSAP256SHA256:
                curve = ecdsa.curves.NIST256p
                key_len = 32
            elif rrsig.algorithm == ECDSAP384SHA384:
                curve = ecdsa.curves.NIST384p
                key_len = 48
            else:
                # shouldn't happen
                raise ValidationFailure('unknown ECDSA curve')
            keyptr = candidate_key.key
            x = ecdsa.util.string_to_number(keyptr[0:key_len])
            y = ecdsa.util.string_to_number(keyptr[key_len:key_len * 2])
            assert ecdsa.ecdsa.point_is_valid(curve.generator, x, y)
            point = ecdsa.ellipticcurve.Point(curve.curve, x, y, curve.order)
            verifying_key = ecdsa.keys.VerifyingKey.from_public_point(point, curve)
            r = rrsig.signature[:key_len]
            s = rrsig.signature[key_len:]
            sig = ecdsa.ecdsa.Signature(ecdsa.util.string_to_number(r),
                                        ecdsa.util.string_to_number(s))

        else:
            raise ValidationFailure('unknown algorithm %u' % rrsig.algorithm)

        hash.update(_to_rdata(rrsig, origin)[:18])
        hash.update(rrsig.signer.to_digestable(origin))

        if rrsig.labels < len(rrname) - 1:
            suffix = rrname.split(rrsig.labels + 1)[1]
            rrname = dns.name.from_text('*', suffix)
        rrnamebuf = rrname.to_digestable(origin)
        rrfixed = struct.pack('!HHI', rdataset.rdtype, rdataset.rdclass,
                              rrsig.original_ttl)
        rrlist = sorted(rdataset)
        for rr in rrlist:
            hash.update(rrnamebuf)
            hash.update(rrfixed)
            rrdata = rr.to_digestable(origin)
            rrlen = struct.pack('!H', len(rrdata))
            hash.update(rrlen)
            hash.update(rrdata)

        digest = hash.digest()

        if _is_rsa(rrsig.algorithm):
            digest = _make_algorithm_id(rrsig.algorithm) + digest
            if pubkey.verify(bytearray(sig), bytearray(digest)):
                return

        elif _is_ecdsa(rrsig.algorithm):
            diglong = ecdsa.util.string_to_number(digest)
            if verifying_key.pubkey.verifies(diglong, sig):
                return

        else:
            raise ValidationFailure('unknown algorithm %s' % rrsig.algorithm)

    raise ValidationFailure('verify failure')


# replace validate_rrsig
dns.dnssec._validate_rrsig = python_validate_rrsig
dns.dnssec.validate_rrsig = python_validate_rrsig
dns.dnssec.validate = dns.dnssec._validate



from .logging import get_logger


_logger = get_logger(__name__)


# 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 Exception('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 Exception("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 BaseException as e:
        _logger.info(f"DNSSEC error: {str(e)}")
        resolver = dns.resolver.get_default_resolver()
        out = resolver.query(url, rtype)
        validated = False
    return out, validated