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https://github.com/halbert-anderson/decoder-ring-app-assessment

This Decoder Ring application implements three classic cipher algorithms to encode and decode messages: Caesar Shift, Polybius Square, and Substitution Cipher. Mocha and Chai were used to write unit test for the code.
https://github.com/halbert-anderson/decoder-ring-app-assessment

chai mocha nodejs react

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This Decoder Ring application implements three classic cipher algorithms to encode and decode messages: Caesar Shift, Polybius Square, and Substitution Cipher. Mocha and Chai were used to write unit test for the code.

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README 

        
# Decoder Ring



This Decoder Ring application was created as part of a surprise birthday party preparation for a friend who loves escape rooms and puzzles; the goal of the project is to write 

three different classic cipher algorithms to encode and decode messages: Caesar Shift, Polybius Square, and Substitution Cipher.

The project is designed to practice algorithm-building and test-driven development (TDD) skills, as such, the code was more complicated than my prior projects

and I wrote unit tests for the code to assure that it is working the way it is suppose to.  



## Technologies Used

  + **JavaScript:** The core programming language used for building the algorithms.

  + **Node.js:** The JavaScript runtime environment used to execute the project's server-side code and manage dependencies through npm.

  + **Mocha:** Testing framework for running the unit tests.

  + **Chai:** Assertion library used for writing test cases.

    

## Table of Contents



- [Project Overview](#project-overview)

- [Technologies Used](#technologies-used)

- [Learning Objectives](#learning-objectives)

- [Project Setup](#project-setup)

- [Usage](#usage)

- [Cipher Descriptions](#cipher-descriptions)

  - [Caesar Shift Cipher](#caesar-shift-cipher)

  - [Polybius Square Cipher](#polybius-square-cipher)

  - [Substitution Cipher](#substitution-cipher)

- [Testing](#testing)



## Project Overview



This project allows encoding and decoding of messages using the following methods:

- **Caesar Shift Cipher** - The Ceasar method shifts the alphabet by a certain amount and every letter of the origianl message can be coded and decoded using the shifted alphabets.

- **Polybius Square Cipher** - The Polybius method uses a 5-by-5 grid on an x/y axis to define what each alphabet is coded to, so each alphabet 

character has a pair of numbers to define it. 

- **Substitution Cipher** - The Substitution method simply transposes 26 unique characters to the original alphabet and 

uses the transposed chracters as the key for cipher.



### Key Features

- Encodes and decodes messages.

- Implements the ciphers to maintain spaces and special characters.

- Handles edge cases (like wrapping around the alphabet or handling non-alphabetic characters).

- Tests implemented using TDD with Mocha and Chai.



## Learning Objectives



This project tests your ability to:

- Build complex algorithms to solve encoding and decoding problems.

- Write unit tests using Mocha and Chai to test your algorithms.

- Follow a TDD process by writing tests before implementing solutions.



## Project Setup



To run this project on your local machine:



1. Clone the repository:

```bash

git clone https://github.com/your-repo/decoder-ring.git

cd decoder-ring

```

2. Install the necessary dependencies:

  ```bash

  npm install

  ```

3. Run the tests to ensure everything is working:

  ```bash

  npm test

  ```

4. To start the application:

 ```bash

 npm start

```

## Usage

You can use this project to encode and decode messages using any of the three ciphers provided.



Example usage for each cipher:



### Caesar Shift Cipher

  ```bash

  const { caesar } = require('./src/caesar');

  const encoded = caesar("Zebra Magazine", 3);  // "cheud pdjdclqh"

  const decoded = caesar("cheud pdjdclqh", 3, false);  // "zebra magazine"

  ```



### Polybius Square Cipher

```bash

const { polybius } = require('./src/polybius');

const encoded = polybius("message");  // "23513434112251"

const decoded = polybius("23513434112251", false);  // "message"

```



### Substitution Cipher

```bash

const { substitution } = require('./src/substitution');

const encoded = substitution("message", "plmoknijbuhvygctfxrdzeswaq");  // "ykrrpik"

const decoded = substitution("ykrrpik", "plmoknijbuhvygctfxrdzeswaq", false);  // "message"

```



## Cipher Descriptions

### Caesar Shift Cipher

  The Caesar Shift Cipher is a type of substitution cipher where each letter in the plaintext is shifted by a certain number of positions in the alphabet. The key features of this cipher in this project include:



  + Returning `false` if the shift value is 0, less than -25, or greater than 25.

  + Ignoring capital letters.

  + Wrapping around when shifts go past 'z'.

  + Maintaining spaces and special characters.

    

![Ceasar Shift Cipher Screenshot](screenshots/caesarShiftCipher.png)



### Polybius Square Cipher

In the Polybius Square Cipher, each letter is represented by its coordinates in a 5x5 grid. The cipher includes:



  + Translating 'i' and 'j' to 42 when encoding.

  + Translating 42 to 'i/j' when decoding.

  + Ignoring capital letters.

  + Maintaining spaces and non-alphabetic characters.



![Polybius Square Cipher Screenshot](screenshots/polybiusSquareCipher.png)



### Substitution Cipher

The Substitution Cipher replaces each letter in the input with a corresponding letter from a given alphabet. This cipher includes:



  + Returning `false` if the alphabet is not 26 characters long.

  + Returning `false` if there are duplicate characters in the alphabet.

  + Maintaining spaces and non-alphabetic characters.

  + Ignoring capital letters.



![Substitution Cipher Screenshot](screenshots/substitutionCipher.png)



## Testing

This project follows a Test-Driven Development (TDD) approach. Unit tests are written using Mocha and Chai. To run the tests, use:

  ```bash

  npm test

```

The tests cover various cases, such as:



  + Shifting beyond the end of the alphabet for Caesar Cipher.

  + Encoding and decoding spaces and special characters.

  + Handling duplicate characters in the Substitution Cipher alphabet.



## Contributing

Contributions are welcome! If you find any issues or have suggestions for improvements, feel free to submit a pull request.