💡 NeonCaesarCipher 🔐

A minimal Java CLI app that encrypts & decrypts text using the classic Caesar cipher with a custom shift.
_{Simple · Educational · Neon-Styled 🔮}

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🎯 Overview

NeonCaesarCipher is a tiny Java console program that:

• 🔁 Takes a text input from the user
• 🎚 Applies a Caesar cipher with a custom shift k
• 🧩 Shows both the encrypted and decrypted message

It supports:

• ✅ Uppercase letters: A–Z
• ✅ Lowercase letters: a–z
• ✅ Keeps non‑letter characters unchanged (spaces, punctuation, digits, etc.)

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📦 Features

Feature	Description
🔤 Case-sensitive cipher	Uppercase and lowercase handled separately
🎚 Custom shift (k)	You choose how many positions to rotate letters
🔁 Bidirectional	encrypt() and decrypt() implemented
🧮 Wrap-around logic	Shifts correctly wrap inside A–Z / a–z
💻 CLI-based	Runs directly in your terminal / command prompt
📚 Simple, educational example	Great for learning about Caesar ciphers & basic Java input/output

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🧠 How It Works (Caesar Cipher)

The Caesar cipher shifts each letter by k positions in the alphabet.

For encryption:

• For uppercase letters:

  char encryptedCh = (char) (((int) ch - 'A' + Shift) % 26 + 'A');

• For lowercase letters:

  char encryptedCh = (char) (((int) ch - 'a' + Shift) % 26 + 'a');

For decryption, instead of writing new logic, the code reuses encrypt() with a reverse shift:

public String decrypt(String S, int Shift) {
    return encrypt(S, 26 - (Shift % 26));
}

So, decrypt is just:

[ \text{decrypt}(S, k) = \text{encrypt}(S, 26 - (k \bmod 26)) ]

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🗂 Project Structure

NeonCaesarCipher/
├─ src/
│  └─ main/
│     └─ main.java    # Main class with encrypt/decrypt logic and CLI
└─ README.md

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⚙️ Requirements

• ☕ Java JDK 8+ (11, 17, etc. also fine)
• 🖥 Any OS that can run Java:
  • Windows
  • macOS
  • Linux

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🚀 Getting Started

1️⃣ Clone or Download

git clone https://github.com/xedi1/NeonCaesarCipher.git
cd NeonCaesarCipher

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2️⃣ Source Code (main.java)

Make sure your file path is:

src/main/main.java

3️⃣ Compile

From the project root:

cd src
javac main/main.java

This will create main.class inside src/main/.

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4️⃣ Run

From inside src:

java main.main

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🧪 Example Usage

▶ Sample Run #1

Input:

======= Encypt Decode System (Edi)========
Enter String:
HelloWorld
Enter K(Count Movement)
3

Output:

Encrypt Message:KhoorZruog
Decrypt Message:HelloWorld

Explanation:

• H -> K, e -> h, l -> o, etc. shifted by 3 positions.
• Decrypting with the same k = 3 returns the original text.

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▶ Sample Run #2 (with non-letters)

If you modify input handling to support spaces and run:

Input:
S = "Hello, World!", k = 5

Encrypted:
Mjqqt, Btwqi!

• Letters are shifted.
• Punctuation and spaces stay the same.

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📚 API / Methods

Method Signature	Description
String encrypt(String S, int Shift)	Encrypts string S by shifting letters by Shift
String decrypt(String S, int Shift)	Decrypts string S using inverse shift

🔐 encrypt(...)

• Loops over each character
• Checks:
  • Character.isUpperCase(ch) → applies uppercase formula
  • Character.isLowerCase(ch) → applies lowercase formula
  • Else → appends character as-is

🔓 decrypt(...)

• Computes the reverse shift:

  26 - (Shift % 26)

• Calls encrypt() with that reverse shift.

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✨ Possible Improvements (Ideas)

You can keep the code as-is, or upgrade it into a more “neon” project:

• 🧵 Support full-line input using nextLine() instead of next()
• 🎚 Allow negative shifts
• 📁 Read/write from files
• 🌈 Add colored output using ANSI escape codes
• 🔒 Add option to brute-force all 26 shifts (for cracking Caesar cipher)
• 🧪 Add unit tests (e.g., with JUnit)

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🧱 Building a Jar (Optional)

From src:

javac main/main.java
jar cfe NeonCaesarCipher.jar main.main main/*.class

Then run:

java -jar NeonCaesarCipher.jar

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🤝 Contributing

Contributions are welcome!

1. 🍴 Fork the repo
2. 🌿 Create a feature branch

   git checkout -b feature/my-cool-feature

3. ✍️ Commit your changes

   git commit -m "Add awesome feature"

4. 📤 Push the branch

   git push origin feature/my-cool-feature

5. 🔁 Open a Pull Request

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🧾 License

This project is free to use for learning & experimentation.
license (Apache 2.0) by creating a Edi.

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📣 Author

• 💻 Original code by Edi
• 🌐 GitHub: https://github.com/xedi1

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💬 Final Notes

NeonCaesarCipher is a neat example of:

• String manipulation in Java
• Using Scanner for console input
• Implementing a classic cryptographic algorithm

Perfect for beginners who want a small but complete Java project in their GitHub.