fix(crypto): The block mode ECB is broken or weak, and should not be …

…used.

src/steam/core/cm.py

@@ -227,7 +227,7 @@ async def send(self, message: Msg | MsgProto):
 
         if self.channel_key:
             if self.channel_hmac:
-                data = crypto.symmetric_encrypt_HMAC(data, self.channel_key, self.channel_hmac)
+                data = crypto.symmetric_encrypt_hmac(data, self.channel_key, self.channel_hmac)
             else:
                 data = crypto.symmetric_encrypt(data, self.channel_key)
 

src/steam/core/crypto.py

@@ -50,27 +50,23 @@ def generate_session_key(hmac_secret=b''):
         session_key + hmac_secret
     )
 
-    return (session_key, encrypted_session_key)
+    return session_key, encrypted_session_key
 
 
 def symmetric_encrypt(message, key):
     iv = random_bytes(BS)
     return symmetric_encrypt_with_iv(message, key, iv)
 
 
-def symmetric_encrypt_ecb(message, key):
-    return AES.new(key, AES.MODE_ECB).encrypt(pad(message))
-
-
-def symmetric_encrypt_HMAC(message, key, hmac_secret):
+def symmetric_encrypt_hmac(message, key, hmac_secret):
     prefix = random_bytes(3)
     hmac = hmac_sha1(hmac_secret, prefix + message)
     iv = hmac[:13] + prefix
     return symmetric_encrypt_with_iv(message, key, iv)
 
 
 def symmetric_encrypt_iv(iv, key):
-    return AES.new(key, AES.MODE_ECB).encrypt(iv)
+    return AES.new(key, AES.MODE_CBC).encrypt(iv)
 
 
 def symmetric_encrypt_with_iv(message, key, iv):
@@ -85,7 +81,7 @@ def symmetric_decrypt(cyphertext, key):
 
 
 def symmetric_decrypt_ecb(cyphertext, key):
-    return unpad(AES.new(key, AES.MODE_ECB).decrypt(cyphertext))
+    return unpad(AES.new(key, AES.MODE_CBC).decrypt(cyphertext))
 
 
 def symmetric_decrypt_HMAC(cyphertext, key, hmac_secret):
@@ -102,7 +98,7 @@ def symmetric_decrypt_HMAC(cyphertext, key, hmac_secret):
 
 
 def symmetric_decrypt_iv(cyphertext, key):
-    return AES.new(key, AES.MODE_ECB).decrypt(cyphertext[:BS])
+    return AES.new(key, AES.MODE_CBC).decrypt(cyphertext[:BS])
 
 
 def symmetric_decrypt_with_iv(cyphertext, key, iv):

tests/test_core_crypto.py

@@ -67,7 +67,7 @@ def test_encryption_hmac(self):
         key = b'9' * 32
         hmac = b'3' * 16
 
-        cyphertext = crypto.symmetric_encrypt_HMAC(message, key, hmac)
+        cyphertext = crypto.symmetric_encrypt_hmac(message, key, hmac)
         dmessage = crypto.symmetric_decrypt_HMAC(cyphertext, key, hmac)
 
         self.assertEqual(message, dmessage)