Merge pull request #172 from cthulahoops/signing

Signing

fedireads/broadcast.py

@@ -63,37 +63,38 @@ def broadcast_task(sender_id, activity, recipients):
     return errors
 
 
-def sign_and_send(sender, activity, destination):
-    ''' crpyto whatever and http junk '''
+def make_signature(sender, destination, date):
     inbox_parts = urlparse(destination)
-    now = http_date()
     signature_headers = [
         '(request-target): post %s' % inbox_parts.path,
         'host: %s' % inbox_parts.netloc,
-        'date: %s' % now
+        'date: %s' % date,
     ]
     message_to_sign = '\n'.join(signature_headers)
-
-    if not sender.private_key:
-        # this shouldn't happen. it would be bad if it happened.
-        raise ValueError('No private key found for sender')
     signer = pkcs1_15.new(RSA.import_key(sender.private_key))
     signed_message = signer.sign(SHA256.new(message_to_sign.encode('utf8')))
-
     signature = {
         'keyId': '%s#main-key' % sender.actor,
         'algorithm': 'rsa-sha256',
         'headers': '(request-target) host date',
         'signature': b64encode(signed_message).decode('utf8'),
     }
-    signature = ','.join('%s="%s"' % (k, v) for (k, v) in signature.items())
+    return ','.join('%s="%s"' % (k, v) for (k, v) in signature.items())
+
+def sign_and_send(sender, activity, destination):
+    ''' crpyto whatever and http junk '''
+    now = http_date()
+
+    if not sender.private_key:
+        # this shouldn't happen. it would be bad if it happened.
+        raise ValueError('No private key found for sender')
 
     response = requests.post(
         destination,
         data=json.dumps(activity),
         headers={
             'Date': now,
-            'Signature': signature,
+            'Signature': make_signature(sender, destination, now),
             'Content-Type': 'application/activity+json; charset=utf-8',
         },
     )

fedireads/incoming.py

@@ -1,6 +1,8 @@
 ''' handles all of the activity coming in to the server '''
 import json
 from base64 import b64decode
+from urllib.parse import urldefrag
+
 from Crypto.Hash import SHA256
 from Crypto.PublicKey import RSA
 from Crypto.Signature import pkcs1_15
@@ -46,7 +48,7 @@ def shared_inbox(request):
         return HttpResponseBadRequest()
 
     try:
-        verify_signature(request)
+        verify_signature(activity.get('actor'), request)
     except ValueError:
         return HttpResponse(status=401)
 
@@ -82,7 +84,24 @@ def shared_inbox(request):
     return HttpResponse()
 
 
-def verify_signature(request):
+def get_public_key(key_actor):
+    try:
+        user = models.User.objects.get(actor=key_actor)
+        public_key = user.public_key
+        actor = user.actor
+    except models.User.DoesNotExist:
+        response = requests.get(
+            key_actor,
+            headers={'Accept': 'application/activity+json'}
+        )
+        if not response.ok:
+            raise ValueError('Could not load public key')
+        user_data = response.json()
+        public_key = user_data['publicKey']['publicKeyPem']
+
+    return RSA.import_key(public_key)
+
+def verify_signature(required_actor, request):
     ''' verify rsa signature '''
     signature_dict = {}
     for pair in request.headers['Signature'].split(','):
@@ -97,15 +116,13 @@ def verify_signature(request):
     except KeyError:
         raise ValueError('Invalid auth header')
 
-    response = requests.get(
-        key_id,
-        headers={'Accept': 'application/activity+json'}
-    )
-    if not response.ok:
-        raise ValueError('Could not load public key')
+    # TODO Use the fragment - actors can have multiple keys?
+    key_actor = urldefrag(key_id).url
 
-    actor = response.json()
-    key = RSA.import_key(actor['publicKey']['publicKeyPem'])
+    if key_actor != required_actor:
+        raise ValueError("Wrong actor created signature.")
+
+    key = get_public_key(key_actor)
 
     comparison_string = []
     for signed_header_name in headers.split(' '):
@@ -125,8 +142,6 @@ def verify_signature(request):
     # raises a ValueError if it fails
     signer.verify(digest, signature)
 
-    return True
-
 
 @app.task
 def handle_follow(activity):

fedireads/tests/test_signing.py

@@ -0,0 +1,92 @@
+from collections import namedtuple
+from urllib.parse import urlsplit
+
+from Crypto import Random
+from Crypto.PublicKey import RSA
+
+import responses
+
+from django.test import TestCase, Client
+from django.utils.http import http_date
+
+from fedireads.models import User
+from fedireads.broadcast import make_signature
+from fedireads.activitypub import get_follow_request
+from fedireads.settings import DOMAIN
+
+Sender = namedtuple('Sender', ('actor', 'private_key', 'public_key'))
+
+class Signature(TestCase):
+    def setUp(self):
+        self.mouse = User.objects.create_user('mouse', 'mouse@example.com', '')
+        self.rat = User.objects.create_user('rat', 'rat@example.com', '')
+        self.cat = User.objects.create_user('cat', 'cat@example.com', '')
+
+        random_generator = Random.new().read
+        key = RSA.generate(1024, random_generator)
+        private_key = key.export_key().decode('utf8')
+        public_key = key.publickey().export_key().decode('utf8')
+
+        self.fake_remote = Sender(
+            'http://localhost/user/remote',
+            private_key,
+            public_key,
+        )
+
+    def send_follow(self, sender, signature, now):
+        c = Client()
+        return c.post(
+            urlsplit(self.rat.inbox).path,
+            data=get_follow_request(
+                sender,
+                self.rat,
+            ),
+            content_type='application/json',
+            **{
+                'HTTP_DATE': now,
+                'HTTP_SIGNATURE': signature,
+                'HTTP_CONTENT_TYPE': 'application/activity+json; charset=utf-8',
+                'HTTP_HOST': DOMAIN,
+            }
+        )
+
+    def test_correct_signature(self):
+        now = http_date()
+        signature = make_signature(self.mouse, self.rat.inbox, now)
+        return self.send_follow(self.mouse, signature, now).status_code == 200
+
+    def test_wrong_signature(self):
+        ''' Messages must be signed by the right actor.
+            (cat cannot sign messages on behalf of mouse)
+        '''
+        now = http_date()
+        signature = make_signature(self.cat, self.rat.inbox, now)
+        assert self.send_follow(self.mouse, signature, now).status_code == 401
+
+    @responses.activate
+    def test_remote_signer(self):
+        responses.add(
+            responses.GET,
+            self.fake_remote.actor,
+            json={'publicKey': {
+                'publicKeyPem': self.fake_remote.public_key
+            }},
+            status=200)
+
+        now = http_date()
+        sender = self.fake_remote
+        signature = make_signature(sender, self.rat.inbox, now)
+        assert self.send_follow(sender, signature, now).status_code == 200
+
+    @responses.activate
+    def test_nonexistent_signer(self):
+        responses.add(
+            responses.GET,
+            self.fake_remote.actor,
+            json={'error': 'not found'},
+            status=404)
+
+        now = http_date()
+        sender = self.fake_remote
+        signature = make_signature(sender, self.rat.inbox, now)
+        assert self.send_follow(sender, signature, now).status_code == 401

requirements.txt

@@ -1,5 +1,5 @@
 celery==4.4.2
-coverage=5.1
+coverage==5.1
 Django==3.0.3
 django-model-utils==4.0.0
 environs==7.2.0
@@ -10,3 +10,4 @@ pycryptodome==3.9.4
 python-dateutil==2.8.1
 redis==3.4.1
 requests==2.22.0
+responses==0.10.14