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Professional Java Security : Symmetric Encryption

PBE Example Code

When decrypting, this program will read the first 8 bytes of the ciphertext and use that as the salt:

import java.security.*;
import javax.crypto.*;
import javax.crypto.spec.*;
import java.util.*;

// This is for BASE64 encoding and decoding

import sun.misc.*;

/**
 *   PBE.java
 */

If you're not using a Sun-based VM, comment out the import sun.misc.* line shown above, and uncomment the following line. This will switch to our BASE64 encoders:

// import com.isnetworks.base64.*;

public class PBE
{
	private static int ITERATIONS = 1000;

	private static void usage()
	{
     System.err.println("Usage: java PBE -e|-d password text");
	 System.exit(1);
	}

public static void main (String[] args)
		throws Exception
{
	if (args.length != 3) usage();

	char[] password = args[1].toCharArray();
	String text = args[2];
	String output = null;

	// Check the first argument: are we encrypting or decrypting?

	if ("-e".equals(args[0])) output = encrypt(password, text);
	else if ("-d".equals(args[0])) output = decrypt(password, text);
	else usage();
	System.out.println(output);
}

private static String encrypt(char[] password, String plaintext)
		throws Exception
{
	// Begin by creating a random salt of 64 bits (8 bytes)

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

	// Create the PBEKeySpec with the given password

	PBEKeySpec keySpec = new PBEKeySpec(password);

	// Get a SecretKeyFactory for PBEWithSHAAndTwofish

	SecretKeyFactory keyFactory =
		SecretKeyFactory.getInstance("PBEWithSHAAndTwofish-CBC");
	
	// Create our key
	
	SecretKey key = keyFactory.generateSecret(keySpec);
	
	// Now create a parameter spec for our salt and iterations
	
	PBEParameterSpec paramSpec = new PBEParameterSpec(salt, ITERATIONS);
	
	// Create a cipher and initialize it for encrypting
	
	Cipher cipher = Cipher.getInstance("PBEWithSHAAndTwofish-CBC");
	cipher.init(Cipher.ENCRYPT_MODE, key, paramSpec);
	
	byte[] ciphertext = cipher.doFinal(plaintext.getBytes());
	
	BASE64Encoder encoder = new BASE64Encoder();
	
	String saltString = encoder.encode(salt);
	String ciphertextString = encoder.encode(ciphertext);
	
	return saltString+ciphertextString;
}
	private static String decrypt(char[] password, String text)
			throws Exception
	{
	// Below we split the text into salt and text strings.
	
	String salt = text.substring(0,12);
	String ciphertext = text.substring(12,text.length());
	
	// BASE64Decode the bytes for the salt and the ciphertext

	BASE64Decoder decoder = new BASE64Decoder();
	byte[] saltArray = decoder.decodeBuffer(salt);
	byte[] ciphertextArray = decoder.decodeBuffer(ciphertext);

	// Create the PBEKeySpec with the given password

	PBEKeySpec keySpec = new PBEKeySpec(password);

	// Get a SecretKeyFactory for PBEWithSHAAndTwofish

	SecretKeyFactory keyFactory =
		SecretKeyFactory.getInstance("PBEWithSHAAndTwofish-CBC");
	
	// Create our key
	
	SecretKey key = keyFactory.generateSecret(keySpec);
	
	// Now create a parameter spec for our salt and iterations
	PBEParameterSpec paramSpec =
		new PBEParameterSpec(saltArray, ITERATIONS);
	
	// Create a cipher and initialize it for encrypting
	
	Cipher cipher = Cipher.getInstance("PBEWithSHAAndTwofish-CBC");
	cipher.init(Cipher.DECRYPT_MODE, key, paramSpec);
	
	// Perform the actual decryption
	
	byte[] plaintextArray = cipher.doFinal(ciphertextArray);
	
	return new String(plaintextArray);
	}
}

Running the Example

After compiling, we can run the example. For example, to encrypt we could type:

	
	C:\> java PBE –e sasquatch "Hello World!"

This will encrypt the string "Hello World!" using PBE with the password of "sasquatch". We should see output similar to the following:

	+xeivHEOb1M=AT/VYJlYIlJoQSMfKryaKw==

We can decrypt the output with:

	C:\> java PBE –d sasquatch "+xeivHEOb1M=AT/VYJlYIlJoQSMfKryaKw=="

and of course, we get our original message returned to us:

	
	Hello World!

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