Game & Watch Encryption Utility

This program allows you to import and export data to and from your Game & Watch: Super Mario Bros. external flash dump. This program supports the main data region encrypted via OTFDEC, and also both NVRAM regions encrypted via AES-GCM.

Configuration

First, you must create your config file. Please use keyinfo.sample.json as a template, filling in the keys and IVs with actual values for the Game & Watch. Save this file as keyinfo.json in your working directory.

The keys may be found in the following offsets in the Game & Watch's memory:

• OTFDEC
  • Key: 0x080106f4
  • Nonce: 0x080106e4
• AES-GCM
  • Key: 0x200011c8
  • IV: 0x200011d8

Note that the program expects the keys as arrays of uints, as this is how the keys are supplied to the HAL inside the firmware. If you are reading the values as bytes, make sure to convert each uint's endian.

Usage

There are two operations, import and export. import encrypts and writes data to the flash dump, while export decrypts and writes data as separate files. They both take the following options:

-c|--config <key-file>     Path to key file
-d|--data <data-file>      Path to main data
-n1|--nvram1 <nvram-file>  Path to first NVRAM copy
-n2|--nvram2 <nvram-file>  Path to second NVRAM copy

Supply -c if you want to point to a different keyinfo.json. The other options can be supplied if you are interested in importing or exporting their respective files.

For example, to dump main data, you could run the following:

GameAndWatchDecrypt export -d main_data.bin spi_flash_dump.bin

where spi_flash_dump.bin is the path to where your flash dump is.

To build a new image, you could run the following:

GameAndWatchDecrypt import -d main_data.bin -n1 nvram1.bin -n2 nvram2.bin new_image.bin

Standalone mode

You may use this program as a standalone encryptor for your own STM32 application. Set the key params for the encryption you are using, then use one of the following commands:

• otfdec: Encrypts/decrypts OTFDEC region. File is "loaded" at file base address in the config, so be sure to set it and your OTFDEC start/end addresses correctly. Replaces plaintext file with ciphertext and vice versa.
• aesenc: Encrypts using AES-GCM. Replaces plaintext file with tag and ciphertext concatenated.
• aesdec: Decrypts using AES-GCM. Replaces the concatenated tag and ciphertext with plaintext.

Each command takes the path of the file you want to operate on and replaces the contents of the file with the resulting data.