README.md

Vigenère Instructions

tl;dr

Vigenère’s cipher improves upon Caesar’s cipher by encrypting messages using a sequence of keys (or, put another way, a keyword).

Specification

Let’s now write a program called vigenere that enables you to encrypt messages using Vigenère’s cipher. At the time the user executes the program, they should decide, by providing a command-line argument, on what the keyword should be for the secret message they’ll provide at runtime.

Usage

Here are a few examples of how the program might work.

$ ./vigenere bacon
plaintext:  Meet me at the park at eleven am
ciphertext: Negh zf av huf pcfx bt gzrwep oz

or for when the user provides a keyword that is not fully alphabetic:

$ ./vigenere 13
Usage: ./vigenere keyword

or for when they don’t provide a keyword at all:

$ ./vigenere
Usage: ./vigenere keyword

or for when they provide too many keywords:

$ ./vigenere bacon and eggs
Usage: ./vigenere keyword

Full instructions available here