I wish I can sign et check signed item validity. I didn't found anything like that.
Did I miss something ?
What do you thing would be the best way ? proxy ? own implmentation ?

There is the AES Context that might be usable for what you are looking for. If you need more encryption algorithms, you’ll probably need to use a C# library with the C# version of Godot or write a C++ GDExtension/GDNative module.