Use specialized exceptions for handling security checks

pyrogram/client.py

@@ -35,6 +35,7 @@ import pyrogram
 from pyrogram import raw
 from pyrogram import utils
 from pyrogram.crypto import aes
+from pyrogram.errors import CDNFileHashMismatch
 from pyrogram.errors import (
     SessionPasswordNeeded,
     VolumeLocNotFound, ChannelPrivate,
@@ -1009,7 +1010,7 @@ class Client(Methods, Scaffold):
                             # https://core.telegram.org/cdn#verifying-files
                             for i, h in enumerate(hashes):
                                 cdn_chunk = decrypted_chunk[h.limit * i: h.limit * (i + 1)]
-                                assert h.hash == sha256(cdn_chunk).digest(), f"Invalid CDN hash part {i}"
+                                CDNFileHashMismatch.check(h.hash == sha256(cdn_chunk).digest())
 
                             f.write(decrypted_chunk)
 

pyrogram/crypto/mtproto.py

@@ -22,6 +22,7 @@ from io import BytesIO
 from os import urandom
 from typing import List
 
+from pyrogram.errors import SecurityCheckMismatch
 from pyrogram.raw.core import Message, Long
 from . import aes
 from ..session.internals import MsgId
@@ -61,7 +62,7 @@ def unpack(
     auth_key_id: bytes,
     stored_msg_ids: List[int]
 ) -> Message:
-    assert b.read(8) == auth_key_id
+    SecurityCheckMismatch.check(b.read(8) == auth_key_id)
 
     msg_key = b.read(16)
     aes_key, aes_iv = kdf(auth_key, msg_key, False)
@@ -69,7 +70,7 @@ def unpack(
     data.read(8)  # Salt
 
     # https://core.telegram.org/mtproto/security_guidelines#checking-session-id
-    assert data.read(8) == session_id
+    SecurityCheckMismatch.check(data.read(8) == session_id)
 
     try:
         message = Message.read(data)
@@ -87,17 +88,17 @@ def unpack(
 
     # https://core.telegram.org/mtproto/security_guidelines#checking-sha256-hash-value-of-msg-key
     # 96 = 88 + 8 (incoming message)
-    assert msg_key == sha256(auth_key[96:96 + 32] + data.getvalue()).digest()[8:24]
+    SecurityCheckMismatch.check(msg_key == sha256(auth_key[96:96 + 32] + data.getvalue()).digest()[8:24])
 
     # https://core.telegram.org/mtproto/security_guidelines#checking-message-length
     data.seek(32)  # Get to the payload, skip salt (8) + session_id (8) + msg_id (8) + seq_no (4) + length (4)
     payload = data.read()
     padding = payload[message.length:]
-    assert 12 <= len(padding) <= 1024
+    SecurityCheckMismatch.check(12 <= len(padding) <= 1024)
-    assert len(payload) % 4 == 0
+    SecurityCheckMismatch.check(len(payload) % 4 == 0)
 
     # https://core.telegram.org/mtproto/security_guidelines#checking-msg-id
-    assert message.msg_id % 2 != 0
+    SecurityCheckMismatch.check(message.msg_id % 2 != 0)
 
     if len(stored_msg_ids) > STORED_MSG_IDS_MAX_SIZE:
         del stored_msg_ids[:STORED_MSG_IDS_MAX_SIZE // 2]
@@ -105,21 +106,21 @@ def unpack(
     if stored_msg_ids:
         # Ignored message: msg_id is lower than all of the stored values
         if message.msg_id < stored_msg_ids[0]:
-            assert False
+            SecurityCheckMismatch.check(False)
 
         # Ignored message: msg_id is equal to any of the stored values
         if message.msg_id in stored_msg_ids:
-            assert False
+            SecurityCheckMismatch.check(False)
 
         time_diff = (message.msg_id - MsgId()) / 2 ** 32
 
         # Ignored message: msg_id belongs over 30 seconds in the future
         if time_diff > 30:
-            assert False
+            SecurityCheckMismatch.check(False)
 
         # Ignored message: msg_id belongs over 300 seconds in the past
         if time_diff < -300:
-            assert False
+            SecurityCheckMismatch.check(False)
 
     bisect.insort(stored_msg_ids, message.msg_id)
 

pyrogram/errors/__init__.py

@@ -18,3 +18,27 @@
 
 from .exceptions import *
 from .rpc_error import UnknownError
+
+
+class SecurityError(Exception):
+    """Generic security error."""
+
+    @classmethod
+    def check(cls, cond: bool):
+        """Raises this exception if the condition is false"""
+        if not cond:
+            raise cls
+
+
+class SecurityCheckMismatch(SecurityError):
+    """Raised when a security check mismatch occurs."""
+
+    def __init__(self):
+        super().__init__("A security check mismatch has occurred.")
+
+
+class CDNFileHashMismatch(SecurityError):
+    """Raised when a CDN file hash mismatch occurs."""
+
+    def __init__(self):
+        super().__init__("A CDN file hash mismatch has occurred.")

pyrogram/session/auth.py

@@ -27,6 +27,7 @@ import pyrogram
 from pyrogram import raw
 from pyrogram.connection import Connection
 from pyrogram.crypto import aes, rsa, prime
+from pyrogram.errors import SecurityCheckMismatch
 from pyrogram.raw.core import TLObject, Long, Int
 from .internals import MsgId
 
@@ -210,33 +211,33 @@ class Auth:
                 # Security checks
                 #######################
 
-                assert dh_prime == prime.CURRENT_DH_PRIME
+                SecurityCheckMismatch.check(dh_prime == prime.CURRENT_DH_PRIME)
                 log.debug("DH parameters check: OK")
 
                 # https://core.telegram.org/mtproto/security_guidelines#g-a-and-g-b-validation
                 g_b = int.from_bytes(g_b, "big")
-                assert 1 < g < dh_prime - 1
+                SecurityCheckMismatch.check(1 < g < dh_prime - 1)
-                assert 1 < g_a < dh_prime - 1
+                SecurityCheckMismatch.check(1 < g_a < dh_prime - 1)
-                assert 1 < g_b < dh_prime - 1
+                SecurityCheckMismatch.check(1 < g_b < dh_prime - 1)
-                assert 2 ** (2048 - 64) < g_a < dh_prime - 2 ** (2048 - 64)
+                SecurityCheckMismatch.check(2 ** (2048 - 64) < g_a < dh_prime - 2 ** (2048 - 64))
-                assert 2 ** (2048 - 64) < g_b < dh_prime - 2 ** (2048 - 64)
+                SecurityCheckMismatch.check(2 ** (2048 - 64) < g_b < dh_prime - 2 ** (2048 - 64))
                 log.debug("g_a and g_b validation: OK")
 
                 # https://core.telegram.org/mtproto/security_guidelines#checking-sha1-hash-values
                 answer = server_dh_inner_data.write()  # Call .write() to remove padding
-                assert answer_with_hash[:20] == sha1(answer).digest()
+                SecurityCheckMismatch.check(answer_with_hash[:20] == sha1(answer).digest())
                 log.debug("SHA1 hash values check: OK")
 
                 # https://core.telegram.org/mtproto/security_guidelines#checking-nonce-server-nonce-and-new-nonce-fields
                 # 1st message
-                assert nonce == res_pq.nonce
+                SecurityCheckMismatch.check(nonce == res_pq.nonce)
                 # 2nd message
                 server_nonce = int.from_bytes(server_nonce, "little", signed=True)
-                assert nonce == server_dh_params.nonce
+                SecurityCheckMismatch.check(nonce == server_dh_params.nonce)
-                assert server_nonce == server_dh_params.server_nonce
+                SecurityCheckMismatch.check(server_nonce == server_dh_params.server_nonce)
                 # 3rd message
-                assert nonce == set_client_dh_params_answer.nonce
+                SecurityCheckMismatch.check(nonce == set_client_dh_params_answer.nonce)
-                assert server_nonce == set_client_dh_params_answer.server_nonce
+                SecurityCheckMismatch.check(server_nonce == set_client_dh_params_answer.server_nonce)
                 server_nonce = server_nonce.to_bytes(16, "little", signed=True)
                 log.debug("Nonce fields check: OK")
 

pyrogram/session/session.py

@@ -29,7 +29,10 @@ from pyrogram import __copyright__, __license__, __version__
 from pyrogram import raw
 from pyrogram.connection import Connection
 from pyrogram.crypto import mtproto
-from pyrogram.errors import RPCError, InternalServerError, AuthKeyDuplicated, FloodWait, ServiceUnavailable
+from pyrogram.errors import (
+    RPCError, InternalServerError, AuthKeyDuplicated, FloodWait,
+    ServiceUnavailable, SecurityCheckMismatch
+)
 from pyrogram.raw.all import layer
 from pyrogram.raw.core import TLObject, MsgContainer, Int, FutureSalt, FutureSalts
 from .internals import MsgId, MsgFactory
@@ -230,7 +233,7 @@ class Session:
                 self.auth_key_id,
                 self.stored_msg_ids
             )
-        except AssertionError:
+        except SecurityCheckMismatch:
             self.connection.close()
             return