Stage 2 task for HNG Internship

encryptor.dart

import 'dart:convert';

class Encryptor {
  final String key;

  Encryptor({required this.key});

  //Encrypt the plain text
  String encrypt(String plainInputText) {
    List<int> textInputBytes =
        utf8.encode(plainInputText); //Encode  Text input to utf8
    List<int> keyBytes = utf8.encode(key); //Encode Key to utf8
    List<int> encryptedBytes = _xor(textInputBytes, keyBytes); //XOR operation

    return base64.encode(encryptedBytes);
  }

  //Decrypt the encrypted text
  String decrypt(String encryptedInputText) {
    List<int> encryptedBytes =
        base64.decode(encryptedInputText); //Decode encrypted text to base64
    List<int> keyBytes = utf8.encode(key); //Encode Key to utf8
    List<int> decryptedBytes = _xor(encryptedBytes, keyBytes); //XOR operation

    return utf8.decode(decryptedBytes);
  }

  // XOR operation
  List<int> _xor(List<int> text, List<int> key) {
    int keyLength = key.length;

    return List.generate(
      text.length,
      (i) =>
          text[i] ^
          key[i %
              keyLength], //ensures the key is repeated to match the length of the text
    );
  }
}

examples.dart

import './encryptor.dart';

void main(List<String> args) {
  
  //Encryption Example
  
  String plainTextExample1 = 'Jonathan is a Manchester United Fan';
  final key1 = 'Football';

  final encryptor1 = Encryptor(key: key1);

  String encryptedTextExample1 = encryptor1.encrypt(plainTextExample1);
  String decryptedTextExample1 = encryptor1.decrypt(encryptedTextExample1);

  print('Example 1. Plain Text: $plainTextExample1, Key: $key1');
  print('Example 1. Encrypted Text: $encryptedTextExample1');
  print('Example 1. Decrypted Text: $decryptedTextExample1');

  print('-----------------------------------');
  
  
  //DecryptionExample
  String encryptedTextExample2 =
      'GzomRyxORTYGDxQNSUFzHRJHEUhUcxYEFBEAWD1UFQ8AAEY8Bg0D';
  final key2 = 'Stage 1';

  final encryptor2 = Encryptor(key: key2);

  String decryptedTextExample2 = encryptor2.decrypt(encryptedTextExample2);

  print('Example 2. Encrypted Text: $encryptedTextExample2, Key: $key2');
  print('Example 2. Decrypted Text: $decryptedTextExample2');
}

examples_input_output.txt

Example Input & Output 1 (Encryption)
 Input Text: Jonathan is a Manchester United Fan, Input Key: Football
 Output: DAABFRYJDQJmBhxUA0EhDSgMBxERFQkeZjoBHRYECEwADgE=    


Example Input & Outut 2 (Decryption)
  Input Text:GzomRyxORTYGDxQNSUFzHRJHEUhUcxYEFBEAWD1UFQ8AAEY8Bg0D, Key: Stage 1   
  Output: HNG Internship is the best in the world

input_output.dart

import 'dart:io';
import './encryptor.dart';

void main(List<String> args) {
  print(
      'Welcome to Ogudu Jonathan Stage 1 Task (Encryption & Decryption Program)');

  while (true) {
    stdout.write(
        'Enter D to initiate Decryption, E to initiate Encryption or Q to Quit: ');
    String? plainText = stdin.readLineSync();

    if (plainText == 'E' || plainText == 'e') {
      stdout.write('Enter the text to encrypt: ');
      String? textToEncrypt = stdin.readLineSync();
      stdout.write('Enter the key: ');
      String? key = stdin.readLineSync();

      if (textToEncrypt != null && key != null) {
        final encryptor = Encryptor(key: key);
        String encryptedText = encryptor.encrypt(textToEncrypt);
        print('Encrypted Text: $encryptedText');
      }
    } else if (plainText == 'D' || plainText == 'd') {
      stdout.write('Enter the text to decrypt: ');
      String? textToDecrypt = stdin.readLineSync();
      stdout.write('Enter the key: ');
      String? key = stdin.readLineSync();

      if (textToDecrypt != null && key != null) {
        final encryptor = Encryptor(key: key);
        String decryptedText = encryptor.decrypt(textToDecrypt);
        print('Decrypted Text: $decryptedText');
      }
    } else if (plainText == 'Q' || plainText == 'q') {
      print('Goodbye!');
      break;
    } else {
      print('Invalid Input');
    }
  }
}

intructions.txt

Intructions on how to use encryptor class (Using examples.dart as reference point);
1. import encryptor class with the below command.
    import './encryptor.dart';

2.  Create a String variable for Input-Text(plain/encrypted) and Key.
      String plainTextExample1 = 'Jonathan is a Manchester United Fan';
      final key1 = 'Football';

3. Initiate an instance for Encryptor Class using the key variable.
    final encryptor1 = Encryptor(key: key1);
    
4. The encryptor class has a method for encryption & decryption as illustrated below.
      encryptor1.encrypt(plainTextExample1);  // For Encryption
       
      encryptor2.decrypt(encryptedTextExample2);  // for Decrytion
       
5. Using the Encryption or Decryption method, the returned String values can be assigned to variables and used where intended.
        String encryptedTextExample1 = encryptor1.encrypt(plainTextExample1);
                            or
        print(encryptor1.encrypt(plainTextExample1));