Enigma In this project you’ll use Ruby to build a tool for cracking an encryption algorithm.
Introduction Learning Goals / Areas of Focus Practice breaking a program into logical components Testing components in isolation and in combination Applying Enumerable techniques in a real context Reading text from and writing text to files Base Expectations You are to build an encryption engine for encrypting, decrypting, and cracking messages.
Additionally, your program will need to read messages from and output them to the file system.
Encryption Notes The encryption is based on rotation. The character map is made up of all the lowercase letters, then the numbers, then space, then period, then comma. New lines will not appear in the message nor character map.
The Key Each message uses a unique encryption key The key is five digits, like 41521 The first two digits of the key are the “A” rotation (41) The second and third digits of the key are the “B” rotation (15) The third and fourth digits of the key are the “C” rotation (52) The fourth and fifth digits of the key are the “D” rotation (21) The Offsets The date of message transmission is also factored into the encryption Consider the date in the format DDMMYY, like 020315 Square the numeric form (412699225) and find the last four digits (9225) The first digit is the “A offset” (9) The second digit is the “B offset” (2) The third digit is the “C offset” (2) The fourth digit is the “D offset” (5) Encrypting a Message Four characters are encrypted at a time. The first character is rotated forward by the “A” rotation plus the “A offset” The second character is rotated forward by the “B” rotation plus the “B offset” The third character is rotated forward by the “C” rotation plus the “C offset” The fourth character is rotated forward by the “D” rotation plus the “D offset” Decrypting a Message The offsets and keys can be calculated by the same methods above. Then each character is rotated backwards instead of forwards.
Cracking a Key When the key is not known, the offsets can still be calculated from the message date. We believe that each enemy message ends with the characters "..end..". Use that to determine when you’ve correctly guessed the key.
Usage Then we’ll exercise the functionality from a Pry session:
require './lib/enigma' e = Enigma.new my_message = "this is so secret ..end.." output = e.encrypt(my_message) => # encrypted message here output = e.encrypt(my_message, "12345", Date.today) #key and date are optional (gen random key and use today's date) => # encrypted message here e.decrypt(output, "12345", Date.today) => "this is so secret ..end.." e.decrypt(output, "12345") # Date is optional (use today's date) => "this is so secret ..end.." e.crack(output, Date.today) => "this is so secret ..end.." e.crack(output) # Date is optional, use today's date => "this is so secret ..end.." Working with Files In addition to the pry form above, we’ll want to use the tool from the command line like so:
$ ruby ./lib/encrypt.rb message.txt encrypted.txt Created 'encrypted.txt' with the key 82648 and date 030415 That will take the plaintext file message.txt and create an encrypted file encrypted.txt.
Then, if we know the key, we can decrypt:
$ ruby ./lib/decrypt.rb encrypted.txt decrypted.txt 82648 030415 Created 'decrypted.txt' with the key 82648 and date 030415 But if we don’t know the key, we can try to crack it with just the date:
$ ruby ./lib/crack.rb encrypted.txt cracked.txt 030415 Created 'cracked.txt' with the cracked key 82648 and date 030415 Development Phases As you work to implement the project here are ideas for some of your first iterations:
- Key Generator It’d be great if instead of random numbers we could generate a legitimate key. Starting from your runner:
Create an instance of a key generator Figure out what, if anything, you’d need to pass in to the object Start writing tests for the key generator object based on the specs above Go through building the implementation Use it from your runner to generate and output a valid key 2. Offsets Before we can start encrypting we probably need to calculate the offsets.
From your runner, create an instance of an offset calculator Pass the current date and the generated key into the offset calculator Write tests and implementation around the idea of being able to pass in the date and key, then query the A, B, C, and D final rotations 3. Encryption Now that you have all the components you’re ready to encrypt a message.
Create an encryptor object in your runner What information would the encryptor need to be “setup” and ready to encrypt messages? Pass that in. Call an encrypt method and pass in a string message. Get back the encrypted version. 4. Next Steps Now you should have all the components in place such that your command-line encryption is working! Next up:
Follow a similar flow to develop the decrypt script and functionality Swap some encrypted messages with a classmate and see if each other can decrypt them correctly Start experimenting with the cracking functionality Extension Character Support Improve your system so it supports all of the following:
all capital letters all lowercase letters all numbers spaces these symbols: !@#$%^&*()[],.<>;:/?| Support Tooling Please make sure that, before your evaluation, your project has the following:
SimpleCov reporting accurate test coverage statistics HoundCI HoundCI Pull Request based linter. (This should be set up when you start your project.) Evaluation Rubric The project will be assessed with the following guidelines:
4: Above expectations 3: Meets expectations 2: Below expectations 1: Well-below expectations Expectations:
- Ruby Syntax & Style Applies appropriate attribute encapsulation Developer creates instance and local variables appropriately Naming follows convention (is idiomatic) Ruby methods used are logical and readable Developer implements appropriate enumerable methods (#each is used only when necessary) Code is indented properly Code does not exceed 80 characters per line Each class has correctly-named files and corresponding test files in the proper directories Code has been linted and corrected properly.
4: Above expectations 3: Meets expectations 2: Below expectations 1: Well-below expectations 2. Breaking Logic into Components Code is effectively broken into methods & classes Developer writes methods less than 8 lines Methods do not break the principle of SRP
4: Above expectations 3: Meets expectations 2: Below expectations 1: Well-below expectations 3. Test-Driven Development Each method is tested Functionality is accurately covered Tests implement Ruby syntax & style Balances unit and integration tests Evidence of edge cases testing Test Coverage metrics are present (SimpleCov) Test Coverage metrics exceed 95%
4: Above expectations 3: Meets expectations 2: Below expectations 1: Well-below expectations 4. Git Workflow Repository demonstrates that each member of team has contributed fairly equally. Developers commit at a rate of approximately one commit every 30 minutes. Repository shows the use of branches. Developers use a pull request workflow. Developers resolve HoundCI complaints in their pull requests.
4: Above expectations 3: Meets expectations 2: Below expectations 1: Well-below expectations 5. Functionality Application meets all requirements (extensions not required for a 3)
4: Above expectations 3: Meets expectations 2: Below expectations 1: Well-below expectations Erik's Policy here