audiocat-clark 0.11
Encrypted audio tunnel for secure chat, file transfer and remote shell on Linux.
License: MIT
Keywords: chat, messenger, remote shell, remote control, reverse shell, file transfer, modem, audio, cryptography, encryption, security, cybersecurity, linux, gpg, minimodem, e2ee, data diode

<!-- # ![plot](./audiocat_clark/audiocat.png) -->
![plot](https://raw.githubusercontent.com/ClarkFieseln/audiocat/refs/heads/main/audiocat_clark/audiocat.png)

# audiocat
Audiocat is a command-line utility for Linux that reads and writes encrypted data across peer-to-peer or broadcast audio connections, using [minimodem](https://github.com/kamalmostafa/minimodem "minimodem") and [gpg](https://github.com/gpg/gnupg "gpg").

It is a powerful tool that can be combined with any audio infrastructure (like PSTN, cellular network, internet, radio, walkie-talkies) to provide a secure communication channel through an audio tunnel.

The audio interfaces behave like data-diodes, each allowing unidirectional data transmission only, thus preventing data-leaks and malware-injection.

This enables an "enhanced"-end-to-end encryption (E-E2EE) which notably increases security and privacy, especially when the end devices are completely offline (air-gapped-system), thus providing an effective barrier against "legal or illegal" client-side-scanning!

See also <https://www.codeproject.com/Articles/5295970/Audio-Chat-for-Quite-Good-Privacy-AC4QGP>


## Installation
```
  pip install audiocat-clark
```

   or with git:

```
  git clone https://github.com/ClarkFieseln/audiocat.git

  cd audiocat_clark

  chmod +x audiocat

  chmod +x *.sh
```
   
  during first execution you will be asked to install dependencies: minimodem, gpg, bc
  
  but you can also install them yourself with:
```
  sudo apt install minimodem
  sudo apt install gpg
  sudo apt install bc
```
  The package gnome-terminal is assumed to be already installed, install otherwise or change cfg/terminal.

## How to use (pip installation)
### Chat/Messenger

```
  audiocat -c
```
enter and confirm password

On the other device a chat or a remote shell can be started.

### Remote Shell

```
  audiocat -s
```
then enter and confirm password

On the other device a chat shall be started to command the remote shell.

Note that this is technically a "reverse shell" which gives access to your system!

### File Transfer

```
  audiocat -f
```
enter and confirm password

On the other device a file transfer shall be started.

### Probe
To check connectivity and adjust volumes if required.

```
  audiocat -p
```

In addition, a separate terminal will be opened to read unencrypted probe messages being sent by the other side.

## Configuration
Adapt the configuration as required using the 'terminal GUI' with:

```
  audiocat -g
```
<!-- # ![plot](./img/terminal_gui.jpg) -->
![plot](https://raw.githubusercontent.com/ClarkFieseln/audiocat/refs/heads/main/img/terminal_gui.jpg)

Alternatively, you may change the configuration by editing the files in the cfg folder directly. The 'Location' can be found with:

```
  audiocat -d
```

The most important settings are:

* baud
* keepalive_time_sec
* retransmission_timeout_sec
* split_tx_lines
* volume_microphone
* volume_speaker_left
* volume_speaker_right

## How to use (git installation)
When installed with git, audiocat may be called with: 

```
  python3 audiocat.py -c
  # or
  ./audiocat -c
```
This is an example to start a chat, but this is the same for any other option.

For more information check the [documentation](https://github.com/ClarkFieseln/audiocat/blob/main/doc/documentation.md).

## Features
on top of the audio modem provided by minimodem and encryption provided by GPG, audiocat offers a reliable transport layer and many other features:

- modes: chat, remote-shell, file transfer (future: sniffer)
  
- text-to-speech (TTS): synthesize speech from the text received in the chat

- full-duplex communication

- retransmit messages automatically after communication errors

- split big messages into smaller data chunks in order to increase the probability of reception, thus reducing retransmissions

- [keepalive] messages
  
- redundant transmission of "data-messages"
   
- composition of piped commands hidden to the user

- tmp folder located in a configurable path beneath $HOME, independent of the current path.

- probe, to check volume on receiver and adjust manually if needed

  (very high and very low volumes may produce signal distortions)
  
- "braodcast" transmissions also possible, e.g. when ACKs are deactivated

   use-case: walkie-talkie, Radio station, ...
   
- several configuration options: preamble, trailer, delays, cipher algorithm, confidence, log to file, verbose, etc.

## Possible Abuses
please don't do the following if you are not allowed (it might be illegal!):

- exfiltrate data over the air or cable to a nearby or remote computer

- remote control over the air or cable from a nearby or remote computer

- exfiltrate data from a computer evading classical auditing

  (be aware that if you do this on your employer's computer you might be infringing the law!)
  
- use the tool as a "side-channel" for covert communication e.g. to spread or inject malware,

  even worse when combined with steganography (e.g. low volumes, data hidden in noise)
  
## Typical Configuration

<!-- # ![plot](./img/figure2.jpg) -->
![plot](https://raw.githubusercontent.com/ClarkFieseln/audiocat/refs/heads/main/img/figure2.jpg)
A: audiocat in offline PC (Alice)

D: audiocat in offline PC (Bob)

B, C: smartphone with call session (mobile, messenger app, etc.)

diodes: audio connections (sink/speaker -> source/microphone)

## Communication in Linux over Linphone

<!-- # ![plot](./screenshots/20250128_153603.jpg) -->
![plot](https://raw.githubusercontent.com/ClarkFieseln/audiocat/refs/heads/main/screenshots/20250128_153603.jpg)

A: audiocat in offline PC (Alice)

D: audiocat in offline PC (Bob)

B, C: smartphone with [Linphone](https://www.linphone.org) call session

## Communication in Termux over qTox

<!-- # ![plot](./screenshots/20250114_121116.jpg) -->
![plot](https://raw.githubusercontent.com/ClarkFieseln/audiocat/refs/heads/main/screenshots/20250114_121116.jpg)

A: audiocat in offline smartphone with Termux (Alice)

D: audiocat in offline smartphone with Termux (Bob)

B, C: PC with qTox call session

## Communication in Linux over Walkie Talkies

<!-- # ![plot](./screenshots/20241231_140418.jpg) -->
![plot](https://raw.githubusercontent.com/ClarkFieseln/audiocat/refs/heads/main/screenshots/20241231_140418.jpg)

## Split Configuration

<!-- # ![plot](./img/figure3.jpg) -->
![plot](https://raw.githubusercontent.com/ClarkFieseln/audiocat/refs/heads/main/img/figure3.jpg)

A: audiocat in offline PC (Alice)

D: audiocat in offline PC (Bob)

B1, B2, C1, C2: waklie-talkie

## Text-to-speech (TTS)

<!-- # ![plot](./img/tts.jpg) -->
[![Text-to-speech](https://raw.githubusercontent.com/ClarkFieseln/audiocat/refs/heads/main/img/tts.jpg)](https://www.youtube.com/watch?v=fSdJY9vLBVk&list=PLX24fhcibpHUx7ej_Tp4neobJUqOkqliN&index=11)

The text received in the chat is synthesized to speech and output to a separate audio interface.

Text-to-speech demo video: https://youtu.be/-ikTdBzhCSw

## Limitations
The data transfer is usually done at low rates, typical of audio systems. Therefore, this tool is not adequate to transmit big files which may take a long time to complete.

## Hints
Avoid using tools like PulseEffects, they may produce glitches!

In PuseEffects you may check the 'Add to Block List' option for minimodem and qtox.

## PyPi Project

https://pypi.org/project/audiocat-clark

## GitHub Project

https://github.com/ClarkFieseln/audiocat

## Documentation

https://github.com/ClarkFieseln/audiocat/blob/main/doc/documentation.md

## Screenshots

https://github.com/ClarkFieseln/audiocat/tree/main/screenshots

## Videos

https://www.youtube.com/playlist?list=PLX24fhcibpHUx7ej_Tp4neobJUqOkqliN

## License

(c) 2025 Clark Fieseln

This repository is licensed under the MIT license. See LICENSE for details.