An implementation of the educational cryptographic algorithm S-DES.
To everyone who wants to understand the working of modern cryptographic algorithms.
S-DES will run through your message and distort each fragment of eight bits using the key you provided to it.
But first, it will need to generate two sub-keys (K1 and K2) because it cannot use directly your main key.
Then, with K1 and K2, it will be able to read your message and pass the pieces through some simple functions named IP, FK, SW and others.
After this, your message will be successfully encrypted.
For a complete explaination of the proccess, see the documentation.