[mai2] Support encryption (#130)

Similar to O.N.G.E.K.I. and CHUNITHM, with the caveat that the obfuscated endpoint is created using `md5(endpoint + salt)` instead of using PBKDF2 like other games.

Tested and confirmed working on FESTiVAL+.

The current implementation is also affected by #129, so I'm open to ideas.

Reviewed-on: Hay1tsme/artemis#130
Co-authored-by: beerpsi <beerpsi@duck.com>
Co-committed-by: beerpsi <beerpsi@duck.com>

titles/mai2/config.py

@@ -1,3 +1,5 @@
+from typing import Dict
+
 from core.config import CoreConfig
 
 
@@ -70,8 +72,32 @@ class Mai2UploadsConfig:
         )
 
 
+class Mai2CryptoConfig:
+    def __init__(self, parent_config: "Mai2Config") -> None:
+        self.__config = parent_config
+
+    @property
+    def keys(self) -> Dict[int, list[str]]:
+        """
+        in the form of:
+        internal_version: [key, iv, salt]
+        key and iv are hex strings
+        salt is a normal UTF-8 string
+        """
+        return CoreConfig.get_config_field(
+            self.__config, "mai2", "crypto", "keys", default={}
+        )
+
+    @property
+    def encrypted_only(self) -> bool:
+        return CoreConfig.get_config_field(
+            self.__config, "mai2", "crypto", "encrypted_only", default=False
+        )
+
+
 class Mai2Config(dict):
     def __init__(self) -> None:
         self.server = Mai2ServerConfig(self)
         self.deliver = Mai2DeliverConfig(self)
         self.uploads = Mai2UploadsConfig(self)
+        self.crypto = Mai2CryptoConfig(self)