Add relayable signature verification for DiasporaComment

federation/entities/base.py

@@ -15,6 +15,7 @@ class BaseEntity(object):
     _children = []
     _allowed_children = ()
     _source_protocol = ""
+    _source_object = None
 
     def __init__(self, *args, **kwargs):
         self._required = []
@@ -33,6 +34,7 @@ class BaseEntity(object):
         2) Make sure all attrs in required have a non-empty value
         3) Loop through attributes and call their `validate_<attr>` methods, if any.
         4) Validate allowed children
+        5) Validate signatures
         """
         attributes = []
         validates = []
@@ -48,6 +50,7 @@ class BaseEntity(object):
         self._validate_required(attributes)
         self._validate_attributes(validates)
         self._validate_children()
+        self._validate_signatures()
 
     def _validate_required(self, attributes):
         """Ensure required attributes are present."""
@@ -82,6 +85,11 @@ class BaseEntity(object):
                     )
                 )
 
+    def _validate_signatures(self):
+        """Override in subclasses where necessary"""
+        pass
+
+
 class GUIDMixin(BaseEntity):
     guid = ""
 
@@ -164,6 +172,7 @@ class SignedMixin(BaseEntity):
     
     This will be needed to for example when relaying content.
     """
+    _sender_key = ""
     signature = ""
 
     def __init__(self, *args, **kwargs):

federation/entities/diaspora/entities.py

@@ -3,6 +3,8 @@ from lxml import etree
 
 from federation.entities.base import Comment, Post, Reaction, Relationship, Profile, Retraction
 from federation.entities.diaspora.utils import format_dt, struct_to_xml, get_base_attributes
+from federation.exceptions import SignatureVerificationError
+from federation.protocols.diaspora.signatures import verify_relayable_signature
 from federation.utils.diaspora import retrieve_and_parse_profile
 
 
@@ -39,6 +41,13 @@ class DiasporaComment(DiasporaEntityMixin, Comment):
         ])
         return element
 
+    def _validate_signatures(self):
+        super()._validate_signatures()
+        if not self._sender_key:
+            raise SignatureVerificationError("Cannot verify entity signature - no sender key available")
+        if not verify_relayable_signature(self._sender_key, self._source_object, self.signature):
+            raise SignatureVerificationError("Signature verification failed.")
+
 
 class DiasporaPost(DiasporaEntityMixin, Post):
     """Diaspora post, ie status message."""

federation/entities/diaspora/mappers.py

@@ -4,10 +4,10 @@ from datetime import datetime
 
 from lxml import etree
 
-from federation.entities.base import Image, Relationship, Post, Reaction, Comment, Profile, Retraction
+from federation.entities.base import Image, Relationship, Post, Reaction, Comment, Profile, Retraction, SignedMixin
 from federation.entities.diaspora.entities import (
     DiasporaPost, DiasporaComment, DiasporaLike, DiasporaRequest, DiasporaProfile, DiasporaRetraction)
-
+from federation.utils.diaspora import retrieve_and_parse_profile
 
 logger = logging.getLogger("federation")
 
@@ -43,7 +43,7 @@ def xml_children_as_dict(node):
     return dict((e.tag, e.text) for e in node)
 
 
-def element_to_objects(tree):
+def element_to_objects(tree, sender_key_fetcher=None):
     """Transform an Element tree to a list of entities recursively.
 
     Possible child entities are added to each entity `_children` list.
@@ -62,6 +62,18 @@ def element_to_objects(tree):
         if hasattr(cls, "fill_extra_attributes"):
             transformed = cls.fill_extra_attributes(transformed)
         entity = cls(**transformed)
+        # Add protocol name
+        entity._source_protocol = "diaspora"
+        # Save element object to entity for possible later use
+        entity._source_object = element
+        # If signable, fetch sender key
+        if issubclass(cls, SignedMixin):
+            if sender_key_fetcher:
+                entity._sender_key = sender_key_fetcher(entity.handle)
+            else:
+                profile = retrieve_and_parse_profile(entity.handle)
+                if profile:
+                    entity._sender_key = profile.public_key
         try:
             entity.validate()
         except ValueError as ex:
@@ -72,8 +84,6 @@ def element_to_objects(tree):
             continue
         # Do child elements
         entity._children = element_to_objects(element)
-        # Add protocol name
-        entity._source_protocol = "diaspora"
         # Add to entities list
         entities.append(entity)
         if cls == DiasporaRequest:
@@ -84,18 +94,20 @@ def element_to_objects(tree):
     return entities
 
 
-def message_to_objects(message):
+def message_to_objects(message, sender_key_fetcher=None):
     """Takes in a message extracted by a protocol and maps it to entities.
 
     :param message: XML payload
     :type message: str
+    :param sender_key_fetcher: Function to fetch sender public key. If not given, key will always be fetched
+        over network
     :returns: list of entities
     """
     doc = etree.fromstring(message)
     if doc[0].tag == "post":
         # Skip the top <post> element if it exists
         doc = doc[0]
-    entities = element_to_objects(doc)
+    entities = element_to_objects(doc, sender_key_fetcher)
     return entities
 
 

federation/protocols/diaspora/signatures.py

@@ -16,10 +16,29 @@ Example Comment payload
 </XML>
 
 TODO:
-* Add method to verify author signature
 * Add method to create author signature
 
 https://diaspora.github.io/diaspora_federation/federation/relayable.html
 
 parent_author_signature part can be skipped as per discussion with Diaspora protcol team.
 """
+from base64 import urlsafe_b64decode
+
+from Crypto.Hash import SHA256
+from Crypto.PublicKey import RSA
+from Crypto.Signature import PKCS1_v1_5
+
+
+def verify_relayable_signature(public_key, doc, signature):
+    """
+    Verify the signed XML elements to have confidence that the claimed
+    author did actually generate this message.
+    """
+    props = []
+    for child in doc:
+        if child.tag not in ["author_signature", "parent_author_signature"]:
+            props.append(child.text)
+    content = ";".join(props)
+    sig_hash = SHA256.new(content.encode("ascii"))
+    cipher = PKCS1_v1_5.new(RSA.importKey(public_key))
+    return cipher.verify(sig_hash, urlsafe_b64decode(signature))

federation/tests/entities/diaspora/test_mappers.py

@@ -73,7 +73,8 @@ class TestDiasporaEntityMappersReceive(object):
         assert photo.public == False
         assert photo.created_at == datetime(2011, 7, 20, 1, 36, 7)
 
-    def test_message_to_objects_comment(self):
+    @patch("federation.entities.diaspora.mappers.DiasporaComment._validate_signatures")
+    def test_message_to_objects_comment(self, mock_validate):
         entities = message_to_objects(DIASPORA_POST_COMMENT)
         assert len(entities) == 1
         comment = entities[0]
@@ -85,6 +86,7 @@ class TestDiasporaEntityMappersReceive(object):
         assert comment.participation == "comment"
         assert comment.raw_content == "((text))"
         assert comment.signature == "((signature))"
+        mock_validate.assert_called_once_with()
 
     def test_message_to_objects_like(self):
         entities = message_to_objects(DIASPORA_POST_LIKE)

federation/tests/protocols/diaspora/test_signatures.py

@@ -0,0 +1,37 @@
+from lxml import etree
+
+from federation.protocols.diaspora.signatures import verify_relayable_signature
+
+xml = "<XML><post><comment><guid>0dd40d800db1013514416c626dd55703</guid><parent_guid>69ab2b83-aa69-4456-ad0a-dd669" \
+      "7f54714</parent_guid><text>Woop Woop</text><diaspora_handle>jaywink@iliketoast.net</diaspora_handle>" \
+      "<author_signature>A/vVRxM3V1ceEH1JrnPOaIZGM3gMjw/fnT9TgUh3poI4q9eH95AIoig+3eTA8XFuGvuo0tivxci4e0NJ1VLVkl/aqp8" \
+      "rvBNrRI1RQkn2WVF6zk15Gq6KSia/wyzyiJHGxNGM8oFY4qPfNp6K+8ydUti22J11tVBEvQn+7FPAoloF2Xz1waK48ZZCFs8Rxzj+4jlz1Pmu" \
+      "XCnTj7v7GYS1Rb6sdFz4nBSuVk5X8tGOSXIRYxPgmtsDRMRrvDeEK+v3OY6VnT8dLTckS0qCwTRUULub1CGwkz/2mReZk/M1W4EbUnugF5pts" \
+      "lmFqYDYJZM8PA/g89EKVpkx2gaFbsC4KXocWnxHNiue18rrFQ5hMnDuDRiRybLnQkxXbE/HDuLdnognt2S5wRshPoZmhe95v3qq/5nH/GX1D7" \
+      "VmxEEIG9fX+XX+Vh9kzO9bLbwoJZwm50zXxCvrLlye/2JU5Vd2Hbm4aMuAyRAZiLS/EQcBlsts4DaFu4txe60HbXSh6nqNofGkusuzZnCd0VO" \
+      "bOpXizrI8xNQzZpjJEB5QqE2gbCC2YZNdOS0eBGXw42dAXa/QV3jZXGES7DdQlqPqqT3YjcMFLiRrWQR8cl4hJIBRpV5piGyLmMMKYrWu7hQS" \
+      "rdRAEL3K6mNZZU6/yoG879LjtQbVwaFGPeT29B4zBE97FIo=</author_signature><parent_author_signature/></comment>" \
+      "</post></XML>"
+
+signature = "A/vVRxM3V1ceEH1JrnPOaIZGM3gMjw/fnT9TgUh3poI4q9eH95AIoig+3eTA8XFuGvuo0tivxci4e0NJ1VLVkl/aqp8rvBNrRI1RQk" \
+            "n2WVF6zk15Gq6KSia/wyzyiJHGxNGM8oFY4qPfNp6K+8ydUti22J11tVBEvQn+7FPAoloF2Xz1waK48ZZCFs8Rxzj+4jlz1PmuXCnT" \
+            "j7v7GYS1Rb6sdFz4nBSuVk5X8tGOSXIRYxPgmtsDRMRrvDeEK+v3OY6VnT8dLTckS0qCwTRUULub1CGwkz/2mReZk/M1W4EbUnugF5" \
+            "ptslmFqYDYJZM8PA/g89EKVpkx2gaFbsC4KXocWnxHNiue18rrFQ5hMnDuDRiRybLnQkxXbE/HDuLdnognt2S5wRshPoZmhe95v3qq" \
+            "/5nH/GX1D7VmxEEIG9fX+XX+Vh9kzO9bLbwoJZwm50zXxCvrLlye/2JU5Vd2Hbm4aMuAyRAZiLS/EQcBlsts4DaFu4txe60HbXSh6n" \
+            "qNofGkusuzZnCd0VObOpXizrI8xNQzZpjJEB5QqE2gbCC2YZNdOS0eBGXw42dAXa/QV3jZXGES7DdQlqPqqT3YjcMFLiRrWQR8cl4h" \
+            "JIBRpV5piGyLmMMKYrWu7hQSrdRAEL3K6mNZZU6/yoG879LjtQbVwaFGPeT29B4zBE97FIo="
+
+pubkey = "-----BEGIN PUBLIC KEY-----\nMIICIjANBgkqhkiG9w0BAQEFAAOCAg8AMIICCgKCAgEAuCfU1G5X+3O6vPdSz6QY\nSFbgdbv3KPv" \
+         "xHi8tRmlyOLdLt5i1eqsy2WCW1iYNijiCL7OfbrvymBQxe3GA9S64\nVuavwzQ8nO7nzpNMqxY5tBXsBM1lECCHDOvm5dzINXWT9Sg7P1" \
+         "8iIxE/2wQEgMUL\nAeVbJtAriXM4zydL7c91agFMJu1aHp0lxzoH8I13xzUetGMutR1tbcfWvoQvPAoU\n89uAz5j/DFMhWrkVEKGeWt1" \
+         "YtHMmJqpYqR6961GDlwRuUsOBsLgLLVohzlBsTBSn\n3580o2E6G3DEaX0Az9WB9ylhNeV/L/PP3c5htpEyoPZSy1pgtut6TRYQwC8wns" \
+         "qO\nbVIbFBkrKoaRDyVCnpMuKdDNLZqOOfhzas+SWRAby6D8VsXpPi/DpeS9XkX0o/uH\nJ9N49GuYMSUGC8gKtaddD13pUqS/9rpSvLD" \
+         "rrDQe5Lhuyusgd28wgEAPCTmM3pEt\nQnlxEeEmFMIn3OBLbEDw5TFE7iED0z7a4dAkqqz8KCGEt12e1Kz7ujuOVMxJxzk6\nNtwt40Sq" \
+         "EOPcdsGHAA+hqzJnXUihXfmtmFkropaCxM2f+Ha0bOQdDDui5crcV3sX\njShmcqN6YqFzmoPK0XM9P1qC+lfL2Mz6bHC5p9M8/FtcM46" \
+         "hCj1TF/tl8zaZxtHP\nOrMuFJy4j4yAsyVy3ddO69ECAwEAAQ==\n-----END PUBLIC KEY-----\n"
+
+
+def test_verify_relayable_signature():
+    doc = etree.XML(xml)
+    root = doc.find(".//comment")
+    assert verify_relayable_signature(pubkey, root, signature)