03. [50p] Solving a substitution cipher
Time to get your hands dirty! Below, you have a ciphertext. Specifically, this output is the result of a substitution cipher, meaning that every letter in the English alphabet has been assigned a random, unique correspondent. As you may have noticed, digits and special characters remain unchanged.
Your task is to write a Python script that will help you break the cipher and decode the original text:
- read the ciphertext from a file specified as a command line argument
- use a dictionary to map each encoded character back to it's original value
- manually populate this dictionary as you progress in your attempt and reveal new characters
- whenever you run the script, it should print the text to the screen, with a few minor changes:
- any character that exists as a key in the dictionary should be replaced with what you think the correspondent is.
- any replaced character should be highlighted in bold red.
Remember ANSI codes?
$ echo -e "\033[1;34m I'm blue, da ba dee, dabba daa-ee, dabba dee-a dabba da \033[0m"
In breaking a short substitution cipher like this while also knowing the original language, you need to look at bigrams and trigrams. Small groups of letters that have a limited amount of possible values that make sense: “to”, “and”, “the”, etc. As you reveal more and more of the original text, words will begin to form, making everything progressively easier.
If you need an extra hint:
Alternatively, if you want to keep learning python, take a look at these labs for an introduction into NumPy (a fundamental module for numeric computation) and matplotlib (a module for plotting).