import java.lang.Object;
import javax.crypto.*;
import java.security.*;
import java.io.*;
import javax.crypto.spec.SecretKeySpec;
import java.util.Scanner;
public class AESEncryption
{
   public static void main(String[] args)
   {
      Scanner input = new Scanner(System.in);
      System.out.print("Enter E for encyrption or D for decryption: ");
      String a = input.nextLine();
      if(a.equals("E"))
      {
         encrypt();
      }
      else
      {
         decrypt();
      }
   }
   public static void encrypt()
   {
      Scanner input = new Scanner(System.in);
      System.out.print("Enter the file name: ");
      String fileName = input.nextLine();
      File file = new File(fileName);
      try
      {
         // create secret key
         KeyGenerator keyGen = KeyGenerator.getInstance("AES");
         keyGen.init(128);
         SecretKey key = keyGen.generateKey();

         // initialize aes encryption object
         Cipher cipher = Cipher.getInstance("AES");
         cipher.init(Cipher.ENCRYPT_MODE, key);

         // read in bytes
         FileInputStream fis = new FileInputStream(file);
         byte[] byteArray = new byte[(int)file.length()];
         int buffer = fis.read(byteArray);

         // encrypt bytes
         byte[] bArray = cipher.doFinal(byteArray);

         // write bytes (in place)
         FileOutputStream fos = new FileOutputStream(file);
         fos.write(bArray);

         // write key to file
         FileOutputStream encodedKey = new FileOutputStream("key.txt");
         byte[] keys = key.getEncoded();
         encodedKey.write(keys);

         // close result file
         fis.close();
         fos.close();

         // close key file
         encodedKey.close();
      }
      catch(FileNotFoundException fnfe)
      {
         System.out.println("File Not Found");
      }
      catch(IOException ioe)
      {
         System.out.println("Signals that an I/O exception of some sort has occurred.");
      }
      catch(IllegalBlockSizeException ibse)
      {
         System.out.println(" no padding has been requested (only in encryption mode), and the total input length of the data processed by this cipher is not a multiple of block size; or if this encryption algorithm is unable to process the input data provided");
      }
      catch(BadPaddingException bpe)
      {
         System.out.println("if this cipher is in decryption mode, and (un)padding has been requested, but the decrypted data is not bounded by the appropriate padding bytes");
      }
      catch(NoSuchPaddingException nspe)
      {
         System.out.println("a particular padding mechanism is requested but is not available in the environment");
      }
      catch(NoSuchAlgorithmException nsae)
      {
         System.out.println("cryptographic algorithm is requested but is not available in the environment");
      }
      catch(InvalidKeyException ike)
      {
         System.out.println("the given key is inappropriate for initializing this cipher");
      }
   }
   public static void decrypt()
      Scanner input = new Scanner(System.in);
      System.out.print("Enter the file name of whats to be decrypted: ");
      String fileName = input.nextLine();
      System.out.print("Enter the file name of the key: ");
      String keyName = input.nextLine();
      File encryptedFile = new File(fileName);
      File encryptedKey = new File(keyName);
      try
      {
         // load all data
         FileInputStream fisKey = new FileInputStream(encryptedKey);
         FileInputStream fisFile = new FileInputStream(encryptedFile);
         FileOutputStream fos = new FileOutputStream("decryptedFile.txt");

         // initialize output byte array
         byte[] fileArray = new byte[(int)encryptedFile.length()];
         int buffer2 = fisFile.read(fileArray);

         // initialize key byte array
         byte[] keyBytes = new byte[(int)encryptedKey.length()];
         int buffer = fisKey.read(keyBytes);

         // construct secret key from key bytes
         SecretKeySpec key = new SecretKeySpec(keyBytes, "AES");

         // initialize cipher and decrypt
         Cipher cipher = Cipher.getInstance("AES");
         cipher.init(Cipher.DECRYPT_MODE, key);
         byte[] cipherBytes = cipher.doFinal(fileArray);

         // write to file
         fos.write(cipherBytes);
         fisKey.close();
         fos.close();
         fisFile.close();
      }
      catch(FileNotFoundException fnfe)
      {
         System.out.println("File Not Found");
      }
      catch(IOException ioe)
      {
         System.out.println("Signals that an I/O exception of some sort has occurred.");
      }
      catch(IllegalBlockSizeException ibse)
      {
         System.out.println(" no padding has been requested (only in encryption mode), and the total input length of the data processed by this cipher is not a multiple of block size; or if this encryption algorithm is unable to process the input data provided");
      }
      catch(NoSuchPaddingException nspe)
      {
         System.out.println("a particular padding mechanism is requested but is not available in the environment");
      }
      catch(NoSuchAlgorithmException nsae)
      {
         System.out.println("cryptographic algorithm is requested but is not available in the environment");
      }
      catch(InvalidKeyException ike)
      {
         System.out.println("the given key is inappropriate for initializing this cipher");
      }
      catch(NullPointerException npe)
      {
         System.out.println("specified algorithm is null");
      }
      catch(GeneralSecurityException gse)
      {
         System.out.println("bad or invalid padding/block");
      }
   }
}