add DNSSEC chain validation

lib/contacts.py

@@ -1,12 +1,13 @@
 import sys
 import re
 import dns
-import traceback
 
 import bitcoin
+import dnssec
 from util import StoreDict, print_error
 from i18n import _
 
+
 class Contacts(StoreDict):
 
     def __init__(self, config):
@@ -18,7 +19,6 @@ class Contacts(StoreDict):
                 'address': k,
                 'type': 'address'
             }
-
         if k in self.keys():
             _type, addr = self[k]
             if _type == 'address':
@@ -26,62 +26,32 @@ class Contacts(StoreDict):
                     'address': addr,
                     'type': 'contact'
                 }
-
         out = self.resolve_openalias(k)
         if out:
-            address, name = out
-            validated = False
+            address, name, validated = out
             return {
                 'address': address,
                 'name': name,
                 'type': 'openalias',
                 'validated': validated
             }
-
         raise Exception("Invalid Bitcoin address or alias", k)
 
     def resolve_openalias(self, url):
-        '''Resolve OpenAlias address using url.'''
-        print_error('[OA] Attempting to resolve OpenAlias data for ' + url)
-
-        url = url.replace('@', '.')  # support email-style addresses, per the OA standard
+        # support email-style addresses, per the OA standard
+        url = url.replace('@', '.')
+        records, validated = dnssec.query(url, dns.rdatatype.TXT)
         prefix = 'btc'
-        retries = 3
-        err = None
-        for i in range(0, retries):
-            try:
-                resolver = dns.resolver.Resolver()
-                resolver.timeout = 2.0
-                resolver.lifetime = 4.0
-                records = resolver.query(url, dns.rdatatype.TXT)
-                for record in records:
-                    string = record.strings[0]
-                    if string.startswith('oa1:' + prefix):
-                        address = self.find_regex(string, r'recipient_address=([A-Za-z0-9]+)')
-                        name = self.find_regex(string, r'recipient_name=([^;]+)')
-                        if not name:
-                            name = address
-                        if not address:
-                            continue
-                        return (address, name)
-                err = _('No OpenAlias record found.')
-                break
-            except dns.resolver.NXDOMAIN:
-                err = _('No such domain.')
-                continue
-            except dns.resolver.Timeout:
-                err = _('Timed out while resolving.')
-                continue
-            except DNSException:
-                err = _('Unhandled exception.')
-                continue
-            except Exception, e:
-                err = _('Unexpected error: ' + str(e))
-                continue
-            break
-        if err:
-            print_error(err)
-        return 0
+        for record in records:
+            string = record.strings[0]
+            if string.startswith('oa1:' + prefix):
+                address = self.find_regex(string, r'recipient_address=([A-Za-z0-9]+)')
+                name = self.find_regex(string, r'recipient_name=([^;]+)')
+                if not name:
+                    name = address
+                if not address:
+                    continue
+                return address, name, validated
 
     def find_regex(self, haystack, needle):
         regex = re.compile(needle)

lib/dnssec.py

@@ -0,0 +1,123 @@
+#!/usr/bin/env python
+#
+# Electrum - lightweight Bitcoin client
+# Copyright (C) 2015 Thomas Voegtlin
+#
+# This program is free software: you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation, either version 3 of the License, or
+# (at your option) any later version.
+#
+# This program is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+# GNU General Public License for more details.
+#
+# You should have received a copy of the GNU General Public License
+# along with this program. If not, see <http://www.gnu.org/licenses/>.
+
+
+
+# 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 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
+from dns.exception import DNSException
+
+
+from util import print_error
+
+
+# hard-coded root KSK
+root_KSK = 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) == 2, 'No DNSSEC record found'
+    if answer[0].rdtype == dns.rdatatype.RRSIG:
+        rrsig, rrset = answer
+    else:
+        rrset, rrsig = answer
+    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 keys
+    root_rrset = check_query(ns, '', dns.rdatatype.DNSKEY, {dns.name.root: root_KSK})
+    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)
+        # 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:
+                good_ds = dns.dnssec.make_ds(name, dnskey, 'SHA256')
+                if ds == good_ds:
+                    break
+            else:
+                continue
+            break
+        else:
+            print ds_rrset
+            raise BaseException("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):
+    resolver = dns.resolver.get_default_resolver()
+    # 8.8.8.8 is Google's public DNS server
+    resolver.nameservers = ['8.8.8.8']
+    ns = resolver.nameservers[0]
+    try:
+        out = get_and_validate(ns, url, rtype)
+        validated = True
+    except BaseException as e:
+        #traceback.print_exc(file=sys.stderr)
+        print_error("DNSSEC error:", str(e))
+        out = resolver.query(url, rtype)
+        validated = False
+    return out, validated