A simple Encryption and Decryption program in Dart (and Flutter)

README.md

string_encryption_app

A simple string Encryption and Decryption using the Caesar Cipher algorithm.

How to Run

1. Download the files.
2. Run dart encryption_service.dart to execute the Dart program on console.
3. Alternatively, run flutter pub get to install dependencies and flutter run to launch the Flutter app.

Example

• Input: "Hello", Key: "key123"
• Encrypted: "Hkrru"
• Decrypted: "Hello"

encryption_service.dart

class EncryptionService {
  /// A static method that encrypts plain text using some passed key.
  /// Call `EncryptionService.encryptText(plainText, key)` to execute,
  /// ensuring to pass the `plainText` that needs encrypting, and a `key`.
  static String encryptText(String plainText, String key) {
    // Algorithm: Shift each character by the length of the key
    int shift = key.length;
    String encryptedText = "";
    for (int i = 0; i < plainText.length; i++) {
      encryptedText += String.fromCharCode(plainText.codeUnitAt(i) + shift);
    }
    return encryptedText;
  }
  
  /// A static method that decrypts encoded text using a passed key.
  /// Call `EncryptionService.decryptText(plainText, key)` to execute,
  /// ensuring to pass the `plainText` that needs encrypting, and the `key`.
  static String decryptText(String encryptedText, String key) {
    // Reverse the encryption process
    int shift = key.length;
    String plainText = "";
    for (int i = 0; i < encryptedText.length; i++) {
      plainText += String.fromCharCode(encryptedText.codeUnitAt(i) - shift);
    }
    return plainText;
  }
}

// Example usage
void main() {
  String plaintext = "Hello";
  String key = "key123";

  String encrypted = EncryptionService.encryptText(plaintext, key);
  print("Encrypted: $encrypted"); // Output: Encrypted: Khoor

  String decrypted = EncryptionService.decryptText(encrypted, key);
  print("Decrypted: $decrypted"); // Output: Decrypted: Hello
}

main.dart

import 'package:flutter/material.dart';
import 'encryption_service.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.lightBlue),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'String (d)e(n)cryption'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});

  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  final TextEditingController _inputController = TextEditingController();
  final TextEditingController _keyController = TextEditingController();
  String _result = '';

  void _encrypt() {
    String input = _inputController.text;
    String key = _keyController.text;
    setState(() {
      _result = EncryptionService.encryptText(input, key);
    });
    // _inputController.clear();
  }

  void _decrypt() {
    String input = _inputController.text;
    String key = _keyController.text;
    setState(() {
      _result = EncryptionService.decryptText(input, key);
    });
  }

  @override
  void dispose() {
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
      ),
      body: Padding(
        padding: const EdgeInsets.all(16.0),
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          spacing: 16,
          children: <Widget>[
            TextField(
              controller: _inputController,
              decoration: InputDecoration(
                labelText: 'Input String',
                border: OutlineInputBorder(),
              ),
            ),
            TextField(
              controller: _keyController,
              decoration: InputDecoration(
                labelText: 'Secret Key',
                border: OutlineInputBorder(),
              ),
            ),
            Row(
              mainAxisAlignment: MainAxisAlignment.spaceEvenly,
              children: [
                ElevatedButton(
                  onPressed: _encrypt,
                  child: Text('Encrypt'),
                ),
                ElevatedButton(
                  onPressed: _decrypt,
                  child: Text('Decrypt'),
                ),
              ],
            ),
            Column(
              mainAxisAlignment: MainAxisAlignment.start,
              children: [
                Row(
                  spacing: 8,
                  mainAxisAlignment: MainAxisAlignment.center,
                  children: [
                    Text(
                      'Result:',
                      style:
                          TextStyle(fontSize: 18, fontWeight: FontWeight.bold),
                    ),
                    Tooltip(
                      message: 'Double Tap or long press to copy result',
                      child: SelectableText(
                        _result,
                        style: TextStyle(fontSize: 16),
                        toolbarOptions: ToolbarOptions(copy: true),
                      ),
                    ),
                  ],
                ),
                Text(
                  '(Double tap/Long press to copy)',
                  style: TextStyle(fontSize: 12, color: Colors.grey),
                ),
              ],
            ),
          ],
        ),
      ),
    );
  }
}