Enigma!

Encrypting, Cracking, and Decoding Messages with the Command line with Ruby!

Image source¹

Overview

The Enigma Project is based on codebreaking in WW2. British codebreaker, Alan Turing ², with assistance of Polish mathematicians and espionage, cracked the Nazi's enigma encryption, ultimately shortening the war and saving potentially millions of lives. The encryption algorithm was believed to be so secure that it was used to encrypt all German military and broadcasted over open radio.

This encryption algorithm is based on a ceasar cipher with four distinct shifts.

Example

As an example take the message "hello world." A possible shift pattern could be {A => 3, B => 27, C => 2 D => 8} The shift pattern is created through a complex transformation and summation of the date and key which are provided by the user. It is important to note that only valid characters a-z and spaces are encrypted, the rest are simply transcribed.

• In this example, the A shifter would shift every 4th letter of "hello world" to

[k]ell[r] wo[u]ld!

• The B shift would take this last string "kellr would!" and start on the second letter (e) and shift every four. Since there are 27 characters (a-z + spaces) the characters would functionally remain the same

k[e]llr[ ]wo[u]ld!

• The C shift would start on the third letter (l) and shift every fourth letter from this starting position by 2 from "kellr would!" to

ke[n]lr [y]orl[f]!

• the D shift wold start on the fourth letter of "kenlr yorlf!", (l), and transform each fourth letter from the starting position by 8 to

ken[t]r y[w]lf[!]

Although ! should be transformed, since it is not in our set of valid characters, it is left as is.

Thus our string is encrypted via four ceasar cipher shifts from hello_world => kentr ywlf!

Decryption would work in a similar way, just instead of shifting characters forward, characters are shifted backwards to return the original string.

Usage

The Enigma program can be run from the command line. Simply clone the repo and navigate to the root directory. For encryption, use the following syntax, where the first argument is the file containing the plain .txt file to be encrypted and the second argument is the name of the .txt file that will be created with the encrypted text.

ruby ./lib/encrypt.rb message.txt encrypted.txt

Decryption is similar. To decrypt a message, four arguments are required. (1) the encrypted .txt. file, (2) the new file which contains the unencrypted text, (3) the code used for decryption (note this down when encrypting), and (4) the date of encryption in MMDDYY format (for instance April 1, 1932) would be represented 040132.

ruby ./lib/decrypt.rb encrypted.txt decrypted.txt 12345 040132

To crack an encrypted message without knowing the key, use the following syntax (the last argument is the formatted date):

ruby ./lib/crack.rb encrypted.txt cracked.txt 040132

Self Assessment

As part of the submission requirements for this project. I was asked to assess my performance on Functionality, OOP, Ruby Conventions, and TDD according to this rubric.

	Functionality	Object Oriented Programming	Ruby Conventions and Mechanics	Test Driven Development
Score	4	4	3.5	4

Assessment Explanation

• Functionality
• 4 / 4: The cracking method and command line interface is fully integrated into the project.
• Object Oriented Programming
• 4 / 4: The CLIencrypt and CLIdecrypt classes inherit from the parent class CLI. CLIencrypt and CLIdecrypt have different inputs in the command user interface, so splitting them up makes sense to check these inputs are correct and return feedback to the user if not. However, both need to check to make sure that the files are the same and read in data. These 'common' methods are held in the parent class in order to keep classes tight/compact.
• Ruby Conventions and Mechanics
• 3.5 / 4: Overall, best-practice enumerables were used to cut down code length. Most methods are compact with no more than 10 lines and two methods slightly larger at 12 lines.
• Test Driven Development
• 4 / 4: Simple Coverage shows that 100% of the code is tested in RSpec tests. Edge cases are addressed. Testing is compact, following DRY principles and robust. Methods are testing at the unit and integration levels.

Sources

¹ By Kyrah - Based Hack GIF, uploaded 1/4/2021

² Wikipedia contributors. (2022, January 14). Alan Turing. In Wikipedia, The Free Encyclopedia. Retrieved 18:55, January 14, 2022