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JujuforceandClaude Opus 4.6
c896f362ba
When multiple APP files are provided (base seq=0 + delta seq>0), fsdecrypt now automatically links and merges the differencing VHD into the parent using Set-VHD + Merge-VHD (Windows/Hyper-V only). Triggers a single UAC prompt for elevation. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
122 lines
4.3 KiB
Markdown
122 lines
4.3 KiB
Markdown
# fsdecrypt
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Decryptor and extractor for SEGA arcade filesystem containers (fscrypt format).
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Handles AES-128-CBC encrypted container images used on SEGA Nu/ALLS arcade hardware, automatically parsing the embedded BootID header to identify the game and container type, then decrypting and extracting the contents.
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## Features
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- Decrypts OS, APP, and OPTION (DLC) containers
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- Extracts NTFS-based containers (OS/APP) including internal VHD images
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- Extracts ExFAT-based containers (OPTION/DLC packs)
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- **Auto-merges delta update VHDs** with their base on Windows (Hyper-V)
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- Preserves file timestamps during extraction
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- Built-in key database for 70+ game titles
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- Supports external key files for unlisted games
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- Progress bars with transfer speed and ETA
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## Installation
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Requires [Rust](https://www.rust-lang.org/tools/install) 1.56+ (edition 2021).
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```bash
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cargo build --release
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```
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The binary will be at `target/release/fsdecrypt` (or `fsdecrypt.exe` on Windows).
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## Usage
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```
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fsdecrypt [OPTIONS] <FILES>...
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```
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### Arguments
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- `<FILES>...` - One or more encrypted container files (`.app`, `.opt`, etc.)
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### Options
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- `--no-extract` - Decrypt the container to a raw image file without extracting its contents
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- `-h, --help` - Print help
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- `-V, --version` - Print version
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### Examples
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```bash
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# Decrypt and extract an APP container
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fsdecrypt ABCD_1.00.00_20240101120000_0.app
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# Decrypt and extract an OPTION container
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fsdecrypt ABCD_A001_20240101120000_0.opt
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# Process multiple containers at once
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fsdecrypt game_v1.app game_v2.app extras.opt
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# Decrypt only, skip extraction
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fsdecrypt --no-extract ABCD_1.00.00_20240101120000_0.app
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```
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### Delta Updates
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When a game ships incremental updates, you get a base `.app` (seq=0) and one or more delta `.app` files (seq>0). Pass them all together and fsdecrypt handles the rest:
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```bash
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# Base + delta update: fsdecrypt extracts both VHDs, then auto-merges
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fsdecrypt ABCD_1.00.00_20240101120000_0.app ABCD_1.01.00_20240215143000_1_1.00.00.app
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```
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The merge workflow (Windows only, requires Hyper-V):
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1. Both containers are decrypted and their internal VHDs extracted
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2. `Set-VHD` links the delta (differencing) VHD to its parent
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3. `Merge-VHD` merges the delta into the base VHD
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4. A UAC prompt will appear since these cmdlets require elevation
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If you only provide the delta without its base, fsdecrypt will extract the VHD and print a warning with instructions.
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### Output
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By default, the tool extracts container contents directly:
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| Type | Extracted contents |
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|--------|--------------------|
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| OS | `internal_{seq}.vhd` |
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| APP | `internal_{seq}.vhd` (auto-merged if delta + base provided) |
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| OPTION | Directory with all DLC files |
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With `--no-extract`, a raw decrypted image is written instead:
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| Type | Output filename |
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|--------|-----------------|
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| OS | `{os_id}_{version}_{timestamp}_{seq}.ntfs` |
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| APP | `{game_id}_{version}_{timestamp}_{seq}.ntfs` |
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| OPTION | `{game_id}_{option}_{timestamp}_{seq}.exfat` |
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## External Key Files
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For games not in the built-in database, place a key file named `{GAME_ID}.bin` in the working directory:
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- **16 bytes**: AES-128 key only (IV will be derived automatically)
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- **32 bytes**: AES-128 key (first 16 bytes) + IV (last 16 bytes)
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## How It Works
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1. The first 128 bytes of the container are decrypted using a hardcoded master key to obtain the **BootID** header
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2. The BootID contains metadata: game ID, container type, block layout, and an IV mode flag
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3. The game-specific AES-128 key is looked up from the built-in database (or read from an external `.bin` file)
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4. If no IV is hardcoded or the container uses a custom IV, the IV is derived by trial-decrypting the first data page against the expected filesystem header (NTFS or ExFAT magic bytes)
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5. Each 4096-byte page is decrypted independently using AES-128-CBC, with a per-page IV computed by XORing the file IV with the page's file offset
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6. The decrypted stream is parsed as NTFS or ExFAT depending on container type, and contents are extracted
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## Container Types
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| Type | ID | Filesystem | Description |
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|------|----|-----------|-------------|
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| OS | `0x00` | NTFS | Operating system image |
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| APP | `0x01` | NTFS | Game application and assets |
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| OPTION | `0x02` | ExFAT | Downloadable content / option packs |
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## License
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[BSD Zero Clause License](LICENSE) (0BSD)
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