Java File Encryption Decryption using Password Based Encryption (PBE)

In this Java tutorial we will see about what PBE is and how we can use it in Java to encrypt and decrypt a file. In Password based encryption (PBE), a password is chosen and it is used along with a generated salt (key) to encrypt. Then the same password is used along with the salt again to decrypt the file.

The chosen password is exchanged between the parties. This is a type of symmetric key encryption and decryption technique.

This tutorial is a continuation of our Java security series. In the previous tutorial we saw about symmetric AES encryption and decryption using Java Cryptography Extension (JCE).

How PBE Works?

• A user supplied password which is a simple text phrase that can be easily remembered by the user.
• Along with that password text, a random number which is called salt is added and hashed.
• Using this a AES or a DES encryption key is derived and encrypted.
• The password text is shared between the two parties exchanging the encrypted content.
• The receiver, uses the same password  and salt and decrypts the content.
• Here the key is passing or preserving the password phrase in a secure manner.

File Encryption Decryption Example

In the following example, we will have a simple text file for example and use it to encrypt and decrypt it. Any type of file can be used. We use a password phrase as “javapapers” and a salt is generated then "PBEWithMD5AndTripleDES” used for key generation, hashing and encryption. The iteration count used in the example is 100 and larger the number it increases the key space. Salt is written in the file itself.

FileEncryption.java

package com.javapapers.java.security;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.util.Random;

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.PBEParameterSpec;

public class FileEncryption {

	public static void main(String[] args) throws Exception {

		FileInputStream inFile = new FileInputStream("plainfile.txt");
		FileOutputStream outFile = new FileOutputStream("plainfile.des");

		String password = "javapapers";
		PBEKeySpec pbeKeySpec = new PBEKeySpec(password.toCharArray());
		SecretKeyFactory secretKeyFactory = SecretKeyFactory
				.getInstance("PBEWithMD5AndTripleDES");
		SecretKey secretKey = secretKeyFactory.generateSecret(pbeKeySpec);

		byte[] salt = new byte[8];
		Random random = new Random();
		random.nextBytes(salt);

		PBEParameterSpec pbeParameterSpec = new PBEParameterSpec(salt, 100);
		Cipher cipher = Cipher.getInstance("PBEWithMD5AndTripleDES");
		cipher.init(Cipher.ENCRYPT_MODE, secretKey, pbeParameterSpec);
		outFile.write(salt);

		byte[] input = new byte[64];
		int bytesRead;
		while ((bytesRead = inFile.read(input)) != -1) {
			byte[] output = cipher.update(input, 0, bytesRead);
			if (output != null)
				outFile.write(output);
		}

		byte[] output = cipher.doFinal();
		if (output != null)
			outFile.write(output);

		inFile.close();
		outFile.flush();
		outFile.close();
	}

}

FileDecryption.java

package com.javapapers.java.security;

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

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.SecretKeyFactory;
import javax.crypto.spec.PBEKeySpec;
import javax.crypto.spec.PBEParameterSpec;

public class FileDecryption {
	public static void main(String[] args) throws Exception {

		String password = "javapapers";
		PBEKeySpec pbeKeySpec = new PBEKeySpec(password.toCharArray());
		SecretKeyFactory secretKeyFactory = SecretKeyFactory
				.getInstance("PBEWithMD5AndTripleDES");
		SecretKey secretKey = secretKeyFactory.generateSecret(pbeKeySpec);

		FileInputStream fis = new FileInputStream("plainfile.des");
		byte[] salt = new byte[8];
		fis.read(salt);

		PBEParameterSpec pbeParameterSpec = new PBEParameterSpec(salt, 100);

		Cipher cipher = Cipher.getInstance("PBEWithMD5AndTripleDES");
		cipher.init(Cipher.DECRYPT_MODE, secretKey, pbeParameterSpec);
		FileOutputStream fos = new FileOutputStream("plainfile_decrypted.txt");
		byte[] in = new byte[64];
		int read;
		while ((read = fis.read(in)) != -1) {
			byte[] output = cipher.update(in, 0, read);
			if (output != null)
				fos.write(output);
		}

		byte[] output = cipher.doFinal();
		if (output != null)
			fos.write(output);

		fis.close();
		fos.flush();
		fos.close();
	}
}

When you run these programs, you should first create a file named "plainfile.txt" at the project root classpath. One successfully run, the first program will create an encrypted version of this input file and the second program will create the decrypted version of the encrypted file.

Unlimited Strength Policy Files Installation

I am using Java SE 8 and have installed the “Java Cryptography Extension (JCE) Unlimited Strength Jurisdiction Policy Files 8 Download”. Illegal key size message error (“Wrong key size”) can be avoided by installing it.