A simple implementation of "Chaffing and Winnowing" (CaW) as proposed by Ronald L. Rivest.
See: https://people.csail.mit.edu/rivest/chaffing-980701.txt (copy in doc/)
echo "My message" | py encode.py [secret key] > cypher.txt
cat cypher.txt | py decode.py [secret key]
py encode.py -h
py decode.py -h
Python 3.7