Caesar Cipher Decipher Application

This project is a JavaFX application designed to encode and decode text using the Caesar cipher. It provides two deciphering algorithms: Chi-Square Comparison for reliability and Frequency Analysis for efficiency. The application features a graphical user interface (GUI) for user interaction, allowing encoding with a specified or random key and decoding of encrypted text.

Project Structure

Caesar-Decipher/
├── src/
│   ├── main/
│   │   ├── java/
│   │   │   ├── org/example/
│   │   │   │   ├── Main.java              # Entry point for the JavaFX application
│   │   │   │   ├── Controller.java        # Handles UI interactions and logic
│   │   │   │   ├── Logic.java            # Core logic for encoding/decoding
│   │   │   │   └── Distribution.java      # Data model for letter frequency
│   │   ├── resources/
│   │   │   ├── distributions.json         # Letter frequency data for English
│   │   │   └── org/example/ui.fxml        # JavaFX UI layout

Prerequisites

• Java 17 or higher (with JavaFX SDK)
• Required libraries: javafx-controls, javafx-fxml, jackson-databind
• Maven or Gradle for dependency management (optional)

Install dependencies using Maven (example pom.xml snippet):

<dependencies>
    <dependency>
        <groupId>org.openjfx</groupId>
        <artifactId>javafx-controls</artifactId>
        <version>17</version>
    </dependency>
    <dependency>
        <groupId>org.openjfx</groupId>
        <artifactId>javafx-fxml</artifactId>
        <version>17</version>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.15.2</version>
    </dependency>
</dependencies>

Usage

1. Prepare the Environment:

   • Ensure the distributions.json file is placed in src/main/resources/ for letter frequency data.
   • Configure your IDE or build tool to include JavaFX modules (e.g., --module-path and --add-modules for JavaFX).

2. Run the Application:

   • Run Main.java to launch the JavaFX application.
   • The GUI window will open with options for encoding and decoding text.

3. Encoding:

   • Enter plain text in the "Input Plain Text" field.
   • Select a key (1-25) from the dropdown or skip for a random key.
   • Click the "Encode" button to generate encrypted text, displayed in the "Encrypted Text" area along with the key used.

4. Decoding:

   • Enter encrypted text in the "Input Encoded Text" field.
   • Select an algorithm: "Chi-Square Comparison (reliability)" or "Frequency Analysis (efficiency)".
   • Click the "Decode" button to display the decoded text and inferred key in the "Decoded Text" area.
   • Note: Short messages may cause errors due to insufficient data for analysis.

Features

• Encoding:

  • Shifts letters in the input text by a specified or random key (1-25).
  • Preserves case (uppercase/lowercase) and non-letter characters.

• Decoding:

  • Chi-Square Comparison: Uses statistical comparison of letter frequencies to expected English frequencies to find the most likely key.
  • Frequency Analysis: Identifies the key by matching the top 6 frequent letters in the encoded text to common English letters (e.g., 'e', 't', 'a').

• GUI:

  • Built with JavaFX, defined in ui.fxml.
  • Includes text fields for input, dropdowns for algorithm and key selection, and text areas for output.
  • User-friendly design with clear labels and error messages.

Implementation Details

• Main.java: Initializes the JavaFX application, loads the FXML UI, and sets up the controller.
• Controller.java: Manages user interactions, handles encoding/decoding logic, and updates the UI.
• Logic.java: Contains the core logic for Caesar cipher operations, including:
  • Encoding via character shifting.
  • Decoding using Chi-Square or Frequency Analysis.
  • Loading letter frequency data from distributions.json.
• Distribution.java: Defines the data model for letter frequency JSON.
• distributions.json: Contains English letter frequencies used for decoding.
• ui.fxml: Defines the JavaFX layout with input fields, buttons, and output areas.

Notes

• The application assumes input text contains English letters for accurate decoding.
• The distributions.json file is critical for decoding algorithms and must be present in the resources directory.
• Error handling is implemented for invalid inputs (e.g., empty text, short messages).
• The Chi-Square method is more reliable for longer texts, while Frequency Analysis is faster but may be less accurate for short texts.