About a year ago I wrote a Python library that implements ElsieFour (LC4) encryption (Alan Kaminsky 2017). LC4 is designed for human-to-human communication, without requiring a computer.
I’ve recently updated the library to include color-coded verbose output that shows the steps of the algorithm. This can be helpful for learning to manually encrypt and decrypt messages. The verbose output is accessible through both the Python API and the command-line interface (using --verbose).
The source code is available on GitHub:
https://github.com/dstein64/LC4
The package is available on PyPI, the Python Package Index. It can be installed with pip.
$ pip3 install lc4
Kaminsky, Alan. “ElsieFour: A Low-Tech Authenticated Encryption Algorithm For Human-to-Human Communication,” 2017. https://eprint.iacr.org/2017/339.