MeshTNC

This is a host tool for interacting with a MeshTNC device.

Currently, it's able to connect to the device using serial and set the radio settings. It then remains in rxlog mode and parses the incoming data.

MeshCore packets are supported via the MeshCore crate that was recently uploaded. Some packet types are still missing support.

As the packets come in over the interface, they're parsed and if it's possible to find a shared secret that decrypts them then the payload is also parsed. The keys must be in a toml file with the following format:

[[identities]]
name = "Sample 4 TD"
private_key = "f8285b33f3949770f4668be015c325d3ee6dd99c86e44d15ec2a48e157d355470161800938619f83944af343ae996ce433536b324f38e2ae242e8e1cf40649d5"

# ...

[[identities]]
name = "Sample 5 TD"
private_key = "60B176D579DD1F874C38B1AA6476F30BB77E7CCDD325BC718D9C926628B9037445AE4968856CF19453E8D72C19160EB34FDF7E7EC9EFE384A1ACA5573D6F28E5"

[[contacts]]
name = "Sample 1 CT"
public_key = "34569df1f9661916901669666fb8025eccb9ddb0499cddad4c164fec219c8b8f"

# ...

[[contacts]]
name = "Sample 2 CT"
public_key = "12349bdc1f76a0c12149bb15f791dbe42fde02c209b04a85c6f512990c8cedec"

[[groups]]
name = "#bot"
secret = "eb50a1bcb3e4e5d7bf69a57c9dada211"

# ...

[[groups]]
name = "#capitolhill"
secret = "7f281916c8ec32e13c5ef687d182160a"

Installation

The easiest way to install the tool is to install rust using rust.up, then use cargo to install meshtnc:

cargo install meshtnc

This will install the binary in your local cargo-managed path. If running meshtnc from the command line yields a command not found error, ensure that your shell profile is setup to search in cargo's bin directory.

Installation for Wireshark

To use the tool as a wireshark extcap interface, you'll need to make a symlink to the binary in a directory that wireshark knows to look. The most reliable way to learn what this directory is is to open wireshark, then go to Help->About Wireshark->Folders. In that list, there will be a folder labeled "Personal Extcap path" and will be something like /home/<your home>/.local/lib/wireshark/extcap.

Once you know what that folder is, make the directory using a command similar to:

mkdir -p ~/.local/lib/wireshark/extcap

Then navigate to that folder and symlink meshtnc into it. This will allow wireshark to find the program and query it for its available configuration options, and start the interface.

cd ~/.local/lib/wireshark
ln -s $(which meshtnc) ./

Once that's complete, start wireshark, and you should see a new interface name MeshCore Monitor: mc0. If you click the gear next to it, you'll be able to check and set some settings such as the serial port, the radio frequency, bandwidth, etc.

The defaults are set so it should work most of the time with the US recommended settings and /dev/ttyUSB0. When you cliek Start the interface will start, and new meshcore packets should come into the interface.

Usage

This program can be used in two ways. One is via the command-line where it will display packet dissections in real time in a quasi table. If you provided a identities file, then those keys will be used to attempt to decrypt the messages.

The other way it can be used is as a wireshark extcap interface. This useage is describe somewhat above, but the general idea is that wireshark treats it as a newtwork interface for packet capture.

It will display those packets in real time on its display, and parse them up until the encrypted portions. It is my belief that the limitations of the lua package ecosystem prevents packet decryption as a lua plugin to wireshark. Therefore, you'll only be able to investigate the cleartext portions of the packets.