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#!/usr/bin/env python
#
# Validate a TLS certificate with DANE-EE usage.
# Get a TLS certificate from a HTTP server and verify it with
# DANE/DNSSEC. Only supports TLSA usage=3 (DANE-EE)
#
import os.path, sys, socket, hashlib
from M2Crypto import SSL, X509
import getdns
def usage():
print """\
Usage: %s [hostname] [port]\
""" % os.path.basename(sys.argv[0])
sys.exit(1)
def compute_hash(func, string):
"""compute hash of string using given hash function"""
h = func()
h.update(string)
return h.hexdigest()
def get_addresses(hostname):
extensions = {
"return_both_v4_and_v6" : getdns.EXTENSION_TRUE
}
ctx = getdns.Context()
try:
results = ctx.address(name=hostname, extensions=extensions)
except getdns.error, e:
print(str(e))
sys.exit(1)
status = results.status
address_list = []
if status == getdns.RESPSTATUS_GOOD:
for addr in results.just_address_answers:
address_list.append((addr['address_type'], addr['address_data']))
else:
print "getdns.address(): failed, return code: %d" % status
return address_list
def get_tlsa_rdata_set(replies, requested_usage=None):
tlsa_rdata_set = []
for reply in replies:
for rr in reply['answer']:
if rr['type'] == getdns.RRTYPE_TLSA:
rdata = rr['rdata']
usage = rdata['certificate_usage']
selector = rdata['selector']
matching_type = rdata['matching_type']
cadata = rdata['certificate_association_data']
cadata = str(cadata).encode('hex')
if usage == requested_usage:
tlsa_rdata_set.append(
(usage, selector, matching_type, cadata) )
return tlsa_rdata_set
def get_tlsa(port, proto, hostname):
extensions = {
"dnssec_return_only_secure" : getdns.EXTENSION_TRUE,
}
qname = "_%d._%s.%s" % (port, proto, hostname)
ctx = getdns.Context()
try:
results = ctx.general(name=qname,
request_type=getdns.RRTYPE_TLSA,
extensions=extensions)
except getdns.error, e:
print(str(e))
sys.exit(1)
status = results.status
if status == getdns.RESPSTATUS_GOOD:
return get_tlsa_rdata_set(results.replies_tree, requested_usage=3)
else:
print "getdns.general(): failed, return code: %d" % status
return None
def verify_tlsa(cert, usage, selector, matchtype, hexdata1):
if selector == 0:
certdata = cert.as_der()
elif selector == 1:
certdata = cert.get_pubkey().as_der()
else:
raise ValueError("selector type %d not recognized" % selector)
if matchtype == 0:
hexdata2 = hexdump(certdata)
elif matchtype == 1:
hexdata2 = compute_hash(hashlib.sha256, certdata)
elif matchtype == 2:
hexdata2 = compute_hash(hashlib.sha512, certdata)
else:
raise ValueError("matchtype %d not recognized" % matchtype)
if hexdata1 == hexdata2:
return True
else:
return False
if __name__ == '__main__':
try:
hostname, port = sys.argv[1:]
port = int(port)
except:
usage()
tlsa_rdata_set = get_tlsa(port, "tcp", hostname)
for (iptype, ipaddr) in get_addresses(hostname):
print "Connecting to %s at address %s ..." % (hostname, ipaddr)
ctx = SSL.Context()
if iptype == "IPv4":
sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
elif iptype == "IPv6":
sock = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)
else:
raise ValueError, "Unknown address type: %s" % iptype
sock.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
connection = SSL.Connection(ctx, sock=sock)
# set TLS SNI extension if available in M2Crypto on this platform
# Note: the official M2Crypto release does not yet (as of late 2014)
# have support for SNI, sigh, but patches exist.
try:
connection.set_tlsext_host_name(hostname)
except AttributeError:
pass
# Per https://tools.ietf.org/html/draft-ietf-dane-ops, for DANE-EE
# usage, certificate identity checks are based solely on the TLSA
# record, so we ignore name mismatch conditions in the certificate.
try:
connection.connect((ipaddr, port))
except SSL.Checker.WrongHost:
pass
chain = connection.get_peer_cert_chain()
cert = chain[0]
# find a matching TLSA record entry for the certificate
tlsa_match = False
for (usage, selector, matchtype, hexdata) in tlsa_rdata_set:
if verify_tlsa(cert, usage, selector, matchtype, hexdata):
tlsa_match = True
print "Matched TLSA record %d %d %d %s" % \
(usage, selector, matchtype, hexdata)
else:
print "Didn't match TLSA record %d %d %d %s"% \
(usage, selector, matchtype, hexdata)
if not tlsa_match:
print "No Matching DANE-EE TLSA record found."
connection.close()
ctx.close()
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