Support receiving Diaspora new style encrypted JSON payloads

Decrypt the JSON and extract the Magic Envelope inside.

Closes #83

CHANGELOG.md

@@ -2,6 +2,10 @@
 
 ## [unreleased]
 
+### Added
+* New style Diaspora private encrypted JSON payloads are now supported in the receiving side. Outbound private Diaspora payloads are still sent as legacy encrypted payloads. ([issue](https://github.com/jaywink/federation/issues/83))
+    * No additional changes need to be made when calling `handle_receive` from your task processing. Just pass in the full received XML or JSON payload as a string with recipient user object as before.
+
 ### Fixed
 * Fix getting sender from a combination of legacy Diaspora encrypted payload and new entity names (for example `author`). This combination probably only existed in this library.
 * Correctly extend entity `_children`. Certain Diaspora payloads caused `_children` for an entity to be written over by an empty list, causing for example status message photos to not be saved. Correctly do an extend on it. ([issue](https://github.com/jaywink/federation/issues/89))

federation/protocols/diaspora/encrypted.py

@@ -0,0 +1,31 @@
+import json
+from base64 import b64decode
+
+from Crypto.Cipher import PKCS1_v1_5, AES
+from lxml import etree
+
+
+def pkcs7_unpad(data):
+    """Remove the padding bytes that were added at point of encryption."""
+    if isinstance(data, str):
+        return data[0:-ord(data[-1])]
+    else:
+        return data[0:-data[-1]]
+
+
+class EncryptedPayload:
+    """Diaspora encrypted JSON payloads."""
+
+    @staticmethod
+    def decrypt(payload, private_key):
+        """Decrypt an encrypted JSON payload and return the Magic Envelope document inside."""
+        cipher = PKCS1_v1_5.new(private_key)
+        aes_key = json.loads(
+            cipher.decrypt(b64decode(payload.get("aes_key")), sentinel=None)
+        )
+        key = b64decode(aes_key.get("key"))
+        iv = b64decode(aes_key.get("iv"))
+        encrypted_magic_envelope = b64decode(payload.get("encrypted_magic_envelope"))
+        encrypter = AES.new(key, AES.MODE_CBC, iv)
+        content = encrypter.decrypt(encrypted_magic_envelope)
+        return etree.fromstring(pkcs7_unpad(content))

federation/protocols/diaspora/protocol.py

@@ -2,6 +2,7 @@ import json
 import logging
 import warnings
 from base64 import b64decode, urlsafe_b64decode, b64encode, urlsafe_b64encode
+from json import JSONDecodeError
 from urllib.parse import unquote_plus
 
 from Crypto.Cipher import AES, PKCS1_v1_5
@@ -13,6 +14,7 @@ from lxml import etree
 
 from federation.exceptions import EncryptedMessageError, NoSenderKeyFoundError, SignatureVerificationError
 from federation.protocols.base import BaseProtocol
+from federation.protocols.diaspora.encrypted import EncryptedPayload
 from federation.protocols.diaspora.magic_envelope import MagicEnvelope
 
 logger = logging.getLogger("federation")
@@ -55,17 +57,35 @@ class Protocol(BaseProtocol):
 
     Mostly taken from Pyaspora (https://github.com/lukeross/pyaspora).
     """
-    def receive(self, payload, user=None, sender_key_fetcher=None, skip_author_verification=False, *args, **kwargs):
+    def __init__(self):
+        super().__init__()
+        self.encrypted = self.legacy = False
+
+    def get_json_payload_magic_envelope(self, payload):
+        """Encrypted JSON payload"""
+        private_key = self._get_user_key(self.user)
+        return EncryptedPayload.decrypt(payload=payload, private_key=private_key)
+
+    def store_magic_envelope_doc(self, payload):
+        """Get the Magic Envelope, trying JSON first."""
+        try:
+            json_payload = json.loads(payload)
+            logger.debug("diaspora.protocol.store_magic_envelope_doc: json payload: %s", json_payload)
+            self.doc = self.get_json_payload_magic_envelope(json_payload)
+        except JSONDecodeError:
+            # XML payload
+            xml = unquote_plus(payload)
+            xml = xml.lstrip().encode("utf-8")
+            logger.debug("diaspora.protocol.store_magic_envelope_doc: xml payload: %s", xml)
+            self.doc = etree.fromstring(xml)
+
+    def receive(self, payload, user=None, sender_key_fetcher=None, skip_author_verification=False):
         """Receive a payload.
 
         For testing purposes, `skip_author_verification` can be passed. Authorship will not be verified."""
         self.user = user
         self.get_contact_key = sender_key_fetcher
-        # Prepare payload
-        xml = unquote_plus(payload)
-        xml = xml.lstrip().encode("utf-8")
-        logger.debug("diaspora.protocol.receive: xml content: %s", xml)
-        self.doc = etree.fromstring(xml)
+        self.store_magic_envelope_doc(payload)
         # Check for a legacy header
         self.find_header()
         # Open payload and get actual message
@@ -83,7 +103,6 @@ class Protocol(BaseProtocol):
         return self.user.private_key
 
     def find_header(self):
-        self.encrypted = self.legacy = False
         self.header = self.doc.find(".//{"+PROTOCOL_NS+"}header")
         if self.header != None:
             # Legacy public header found