Write docs for compiling the engine with script encryption key

Retrieved from old godot wiki and adapted according to current source:
https://github.com/ScyDev/godot/wiki/Export-Encrypt-Scripts

Co-authored-by: Lukas Sägesser (SkyDev) <[email protected]>

development/compiling/compiling_with_script_encryption_key.rst

@@ -0,0 +1,86 @@
+.. _doc_compiling_with_script_encryption_key:
+
+.. highlight:: shell
+
+Compiling with script encryption key
+====================================
+
+The export dialog gives you the option to encrypt your scripts with an 256bit
+AES key, when releasing your game. This will make sure your scripts are not
+stored in plain text and can not easily be ripped by some script kiddie.
+Of course the key needs to be stored in the binary, but if it's compiled,
+optimized and without symbols, it would take some effort to find it.
+
+For this to work, you need to build the export templates from source,
+with that same key.
+
+Step by step (Linux)
+--------------------
+
+1. Generate a 256bit AES key in HEX. You can use the aes-256-cbc variant from
+   `this service <https://asecuritysite.com/encryption/keygen>`_.
+
+   Alternatively, you can generate it yourself by using OpenSSL:
+
+   ::
+
+       openssl enc -aes-256-cbc -k secret -P -md sha1 > godot.gdkey
+
+   This should output the following to ``godot.gdkey`` file:
+
+   ::
+
+       salt=5786FE8B91CA048A
+       key=D2F90FCC4FCA64B8990F916EF5A73230C1841601D1EA06B2380EC0F530E4EF85
+       iv =047C353AEC9E6C211515E3341BF9C61B
+
+   You can generate the key without redirecting the output to a file, but
+   that way you can minimize the risk of exposing the key.
+
+
+2. Set this key as environment variable in the console that you will use to
+   compile Godot, like this:
+
+   ::
+
+       export SCRIPT_AES256_ENCRYPTION_KEY="your_generated_key"
+
+
+3. Compile Godot export templates and set them as custom export templates
+   in the export preset options.
+
+4. Set the encryption key in the ``Script`` tab of the export preset:
+
+   .. image:: img/script_encryption_key.png
+
+5. Export the project. The game should run with encrypted scripts now.
+
+Possible Errors
+---------------
+
+If you get an error like below, it means the key wasn't properly included in
+your Godot build. Godot is encrypting the scripts during export, but can't read
+them at runtime.
+
+::
+
+   ERROR: open_and_parse: Condition ' String::md5(md5.digest) != String::md5(md5d) ' is true. returned: ERR_FILE_CORRUPT
+      At: core/io/file_access_encrypted.cpp:103
+   ERROR: load_byte_code: Condition ' err ' is true. returned: err
+      At: modules/gdscript/gdscript.cpp:755
+   ERROR: load: Condition ' err != OK ' is true. returned: RES()
+      At: modules/gdscript/gdscript.cpp:2135
+   ERROR: Failed loading resource: res://Node2D.gde
+      At: core/io/resource_loader.cpp:279
+   ERROR: poll: res://Node2D.tscn:3 - Parse Error: [ext_resource] referenced nonexistent resource at: res://Node2D.gd
+      At: scene/resources/scene_format_text.cpp:439
+   ERROR: load: Condition ' err != OK ' is true. returned: RES()
+      At: core/io/resource_loader.cpp:202
+   ERROR: Failed loading resource: res://Node2D.tscn
+      At: core/io/resource_loader.cpp:279
+   ERROR: Failed loading scene: res://Node2D.tscn
+      At: main/main.cpp:1727
+   WARNING: cleanup: ObjectDB Instances still exist!
+        At: core/object.cpp:2081
+   ERROR: clear: Resources Still in use at Exit!
+      At: core/resource.cpp:425

development/compiling/index.rst

@@ -18,3 +18,4 @@ Compiling
    compiling_with_mono
    packaging_godot
    optimizing_for_size
+   compiling_with_script_encryption_key