# s2png — “stuff to PNG”

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This program encodes arbitrary binary data in PNG images that look like noise
and decodes it back. It was originally developed by k0wax
[on SourceForge](http://sourceforge.net/projects/s2png/). I started this fork
to fix a problem that caused s2png 0.01 to segfault when compiled on a modern
operating system. The fork has since accumulated various bug fixes and
improvements. Most recently, I have ported it to Rust. Among other things,
this makes it easier to distribute s2png as a static binary. The fork remains
data-compatible with the original if you don't use the toy encryption feature.


## Installation

Prebuilt binaries are available for x86\_64 Linux and i686 Windows. They are
attached to releases on the
[Releases](https://github.com/dbohdan/s2png/releases) page. Development
(unstable) binaries are also
[automatically built](https://ci.appveyor.com/project/dbohdan/s2png/build/artifacts)
for Windows.

### Installing with Cargo

```shell
cargo install s2png
```

### Building on Debian and Ubuntu

Follow the instructions to build a static Linux binary of s2png from source
on recent Debian and Ubuntu.

1\. Install [Rustup](https://rustup.rs/). Through Rustup add the stable MUSL
target for your CPU.

```sh
rustup target add x86_64-unknown-linux-musl
```

2\. Install the build dependencies.

```sh
sudo apt install build-essential musl-tools
```

3\. Clone this repository. Build the binary.

    git clone https://github.com/dbohdan/s2png
    cd s2png
    make test
    make release-linux

### Cross-compiling for Windows

Follow the instructions to build a 32-bit Intel Windows binary of s2png on
recent Debian and Ubuntu.

1\. Install [Rustup](https://rustup.rs/). Through Rustup add the i686 GNU ABI
Windows target.

```sh
rustup target add i686-pc-windows-gnu
```

2\. Install the build dependencies.

```sh
sudo apt install build-essential mingw-w64
```

3\. Configure Cargo for cross-compilation. Put the following in
`~/.cargo/config`.

```toml
[target.i686-pc-windows-gnu]
linker = "/usr/bin/i686-w64-mingw32-gcc"
```

4\. Clone this repository. Build the binary.

    git clone https://github.com/dbohdan/s2png
    cd s2png
    make release-windows


## Usage

```none
s2png ("stuff to png") version 0.11.1
usage: s2png [-h] [-o filename] [-w width (600) | -s] [-b text]
             [-p hex-key] [-e | -d] file

Store any data in a PNG image.
This version can encode files of up to 16777215 bytes.

  -h            display this message and quit
  -o filename   output the encoded or decoded data to filename
  -w width      set the width of the PNG image output (600 by default)
  -s            make the output image roughly square
  -b text       custom banner text ("" for no banner)
  -p hex-key    encrypt/decrypt the output with a hexadecimal key
                using RC4 (Warning: completely insecure! Do not use this if
                you want actual secrecy.)

Normally s2png detects which operation to perform by the file type. You can
override this behavior with the following switches:
  -e            force encoding mode
  -d            force decoding mode

See README.md for further details.
```


## Examples

To store `foo.mp3` in an image enter the following command:

    s2png foo.mp3

A file named `foo.mp3.png` will be created in the same directory as `foo.mp3`.

Add the `-s` switch to ensure the resulting image is square (give or take a
pixel) and `-b "some text"` to change the text of the banner at the bottom.

    s2png -s -b hello foo.mp3

To decode `decode_me.mp3.png` and retrieve the original file `decode_me.mp3` run
the command

    s2png decode_me.mp3.png

Decode `xyz.png` to `decoded.mp3` with

    s2png -o decoded.mp3 xyz.png


## License

s2png is licensed under the GNU GPL 2.0. See the file `LICENSE`. The
implementation of the RC4 streaming cypher in [`src/rc4/mod.rs`](src/rc4/mod.rs)
is in the public domain. The font from [libgd](https://github.com/libgd/libgd)
is distributed under its BSD-like license. See the file
[`src/font/COPYING.libgd`](src/font/COPYING.libgd).