Java Code House

I have updated the code on request of some followers so that they can directly use this code for their project without requiring to make any changes.
Following changes have been made

• A copy method has been introduced to copy the streams. I reduces unnecessary duplicate codes for copying files.
• Another important update added is that the file decrypted will have the same name it had before encryption along with its extension.
• The last feature added is try with resources. This reduces extra bit of coding to flush and close the streams.

Today I am going to discuss how you can encrypt any file in Java.For encryption we need a key based on which the encryption will be done. Not only that, I will also show how you can decrypt that file and get back the original one. The encryption algorithm can be chosen by the user. Here we will use some classes Cipher,CipherInputStream,CipherOutputStream,SecretKeySpec. One thing you have to always remember is that the same key must be used both for encryption and decryption. We will use Cipher stream classes as only one function call is required for both either reading/writing and encryption/decryption. Otherwise we would have to call update() method for encryption/decryption and then write() for writing to file.
SecretKeySpec class : This class specifies a secret key in a provider-independent fashion and is only useful for raw secret keys that can be represented as a byte array and have no key parameters associated with them, e.g., DES or Triple DES keys.
Cipher class : This class provides the functionality of a cryptographic cipher for encryption and decryption. It forms the core of the Java Cryptographic Extension (JCE) framework. Its getInstance() method is called to get the object based on algorithm. Then the init() method is called for initializing the object with encryption mode and key.
CipherInputStream class : It is composed of an InputStream and a Cipher so that read() methods return data that are read in from the underlying InputStream but have been additionally processed by the Cipher. The Cipher must be fully initialized before being used by a CipherInputStream. It is used for decryption and does read and then update operation.
CipherOutputStream class : Just like above it is also composed of a stream and cipher and the cipher must be fully initialised before using this stream. It is used for encryption purpose.

So below is the code which solves your question how to encrypt a file in Java and also how to decrypt a file. This code actually shows you how to encrypt and decrypt a file using DES or Triple DES in Java.
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The code after update applied

import java.io.InputStream;
import java.io.OutputStream;
import java.io.FileInputStream;
import java.io.FileOutputStream;

import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.CipherOutputStream;
import javax.crypto.spec.SecretKeySpec;

public class FileEncryptor{
    
 private String algo;
 private String path;
 
    public FileEncryptor(String algo,String path) {
     this.algo = algo; //setting algo
     this.path = path;//setting file path
    }
    
    public void encrypt() throws Exception{
         //generating key
         byte k[] = "HignDlPs".getBytes();   
         SecretKeySpec key = new SecretKeySpec(k,algo.split("/")[0]);  
         //creating and initialising cipher and cipher streams
         Cipher encrypt =  Cipher.getInstance(algo);  
         encrypt.init(Cipher.ENCRYPT_MODE, key);
         //opening streams
         FileOutputStream fos =new FileOutputStream(path+".enc");
         try(FileInputStream fis =new FileInputStream(path)){
            try(CipherOutputStream cout=new CipherOutputStream(fos, encrypt)){
                copy(fis,cout);
            }
         }
     }
     
     public void decrypt() throws Exception{
         //generating same key
         byte k[] = "HignDlPs".getBytes();   
         SecretKeySpec key = new SecretKeySpec(k,algo.split("/")[0]);  
         //creating and initialising cipher and cipher streams
         Cipher decrypt =  Cipher.getInstance(algo);  
         decrypt.init(Cipher.DECRYPT_MODE, key);
         //opening streams
         FileInputStream fis = new FileInputStream(path);
         try(CipherInputStream cin=new CipherInputStream(fis, decrypt)){  
            try(FileOutputStream fos =new FileOutputStream(path.substring(0,path.lastIndexOf(".")))){
               copy(cin,fos);
           }
         }
      }
     
  private void copy(InputStream is,OutputStream os) throws Exception{
     byte buf[] = new byte[4096];  //4K buffer set
     int read = 0;
     while((read = is.read(buf)) != -1)  //reading
        os.write(buf,0,read);  //writing
  }
  
     public static void main (String[] args)throws Exception {
      new FileEncryptor("DES/ECB/PKCS5Padding","sample.txt").encrypt();
      new FileEncryptor("DES/ECB/PKCS5Padding","sample.txt.enc").decrypt();
  }
}

The original code before update

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;

import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.CipherOutputStream;
import javax.crypto.spec.SecretKeySpec;

public class FileEncryptor{
    
    private String algo;
    private File file;
 
    public FileEncryptor(String algo,String path) {
     this.algo=algo; //setting algo
     this.file=new File(path); //settong file
    }
    
     public void encrypt() throws Exception{
         //opening streams
         FileInputStream fis =new FileInputStream(file);
         file=new File(file.getAbsolutePath()+".enc");
         FileOutputStream fos =new FileOutputStream(file);
         //generating key
         byte k[] = "HignDlPs".getBytes();   
         SecretKeySpec key = new SecretKeySpec(k,algo.split("/")[0]);  
         //creating and initialising cipher and cipher streams
         Cipher encrypt =  Cipher.getInstance(algo);  
         encrypt.init(Cipher.ENCRYPT_MODE, key);  
         CipherOutputStream cout=new CipherOutputStream(fos, encrypt);
         
         byte[] buf = new byte[1024];
         int read;
         while((read=fis.read(buf))!=-1)  //reading data
             cout.write(buf,0,read);  //writing encrypted data
         //closing streams
         fis.close();
         cout.flush();
         cout.close();
     }
     
     public void decrypt() throws Exception{
         //opening streams
         FileInputStream fis =new FileInputStream(file);
         file=new File(file.getAbsolutePath()+".dec");
         FileOutputStream fos =new FileOutputStream(file);               
         //generating same key
         byte k[] = "HignDlPs".getBytes();   
         SecretKeySpec key = new SecretKeySpec(k,algo.split("/")[0]);  
         //creating and initialising cipher and cipher streams
         Cipher decrypt =  Cipher.getInstance(algo);  
         decrypt.init(Cipher.DECRYPT_MODE, key);  
         CipherInputStream cin=new CipherInputStream(fis, decrypt);
              
         byte[] buf = new byte[1024];
         int read=0;
         while((read=cin.read(buf))!=-1)  //reading encrypted data
              fos.write(buf,0,read);  //writing decrypted data
         //closing streams
         cin.close();
         fos.flush();
         fos.close();
     }
     
     public static void main (String[] args)throws Exception {
         new FileEncryptor("DES/ECB/PKCS5Padding","sample.txt").encrypt();
         new FileEncryptor("DES/ECB/PKCS5Padding","sample.txt.enc").decrypt();
  }
}

NOTE : The generated decrypted file name is not the same as that of original so that you can check whether same contents have been generated or not. You can change this part.
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DOWNLOAD the source from Mediafire

DOWNLOAD the complete file encryptor project from Mediafire
NOTE : the project archive contains the java source file, the sample file for encryption and the encrypted file produced after encryption of sample file.
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AES - 256bits encryption and decryption of file

Search keywords : how to, encrypt, decrypt, files, using DES, for encryption and decryption, java

Happy coding :)