# fsdecrypt

Decryptor and extractor for SEGA arcade filesystem containers (fscrypt format). Works on Windows and Linux, no admin privileges required.

## Installation

Requires [Rust](https://www.rust-lang.org/tools/install).

```bash
cargo build --release
```

The binary will be at `target/release/fsdecrypt` (or `fsdecrypt.exe` on Windows).

## Usage

```bash
fsdecrypt <FILES>...
```

### Examples

```bash
# Extract a game APP container
fsdecrypt ABCD_1.00.00_20240101120000_0.app

# Extract an OPTION/DLC container
fsdecrypt ABCD_A001_20240101120000_0.opt

# Extract multiple files at once
fsdecrypt game_v1.app game_v2.app extras.opt

# Decrypt only (outputs raw .ntfs/.exfat image, no extraction)
fsdecrypt --no-extract ABCD_1.00.00_20240101120000_0.app
```

### Delta Updates

Games often ship incremental updates as a separate `.app` file. Just pass the update file — fsdecrypt will automatically find the base in the same folder and merge them:

```bash
fsdecrypt ABCD_1.01.00_20240215143000_1_1.00.00.app
```

You can also pass both explicitly:

```bash
fsdecrypt ABCD_1.00.00_20240101120000_0.app ABCD_1.01.00_20240215143000_1_1.00.00.app
```

The output folder is named after the input file (e.g. `ABCD_1.01.00_20240215143000_1_1.00.00/`).

## External Key Files

For games not in the built-in key database, place a file named `{GAME_ID}.bin` in the working directory:

- **16 bytes** for key only (IV derived automatically)
- **32 bytes** for key + IV

## License

[BSD Zero Clause License](LICENSE) (0BSD)