An example of encrypting an xml file in Java using bouncy castle

You can view the java doc at http://bouncycastle.org/docs/docs1.6/index.html

You can download examples from this page: http://eu.wiley.com/WileyCDA/WileyTitle/productCd-0764596330,descCd-DOWNLOAD.html

If you don't have any particular reason for using BouncyCastle, you can find a good tutorial and background information on the Java built-in cryptography support with several code examples here.

What type of encryption do you want to perform? Password-based (PBE), symmetric, asymmetric? Its all in how you configure the Cipher.

You shouldn't have to use any BouncyCastle specific APIs, just the algorithms it provides. Here is an example that uses the BouncyCastle PBE cipher to encrypt a String:

import java.security.SecureRandom;
import java.security.Security;

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

import org.bouncycastle.jce.provider.BouncyCastleProvider;

public class PBE {

    private static final String salt = "A long, but constant phrase that will be used each time as the salt.";
    private static final int iterations = 2000;
    private static final int keyLength = 256;
    private static final SecureRandom random = new SecureRandom();

    public static void main(String [] args) throws Exception {
        Security.insertProviderAt(new BouncyCastleProvider(), 1);

        String passphrase = "The quick brown fox jumped over the lazy brown dog";
        String plaintext = "hello world";
        byte [] ciphertext = encrypt(passphrase, plaintext);
        String recoveredPlaintext = decrypt(passphrase, ciphertext);

        System.out.println(recoveredPlaintext);
    }

    private static byte [] encrypt(String passphrase, String plaintext) throws Exception {
        SecretKey key = generateKey(passphrase);

        Cipher cipher = Cipher.getInstance("AES/CTR/NOPADDING");
        cipher.init(Cipher.ENCRYPT_MODE, key, generateIV(cipher), random);
        return cipher.doFinal(plaintext.getBytes());
    }

    private static String decrypt(String passphrase, byte [] ciphertext) throws Exception {
        SecretKey key = generateKey(passphrase);

        Cipher cipher = Cipher.getInstance("AES/CTR/NOPADDING");
        cipher.init(Cipher.DECRYPT_MODE, key, generateIV(cipher), random);
        return new String(cipher.doFinal(ciphertext));
    }

    private static SecretKey generateKey(String passphrase) throws Exception {
        PBEKeySpec keySpec = new PBEKeySpec(passphrase.toCharArray(), salt.getBytes(), iterations, keyLength);
        SecretKeyFactory keyFactory = SecretKeyFactory.getInstance("PBEWITHSHA256AND256BITAES-CBC-BC");
        return keyFactory.generateSecret(keySpec);
    }

    private static IvParameterSpec generateIV(Cipher cipher) throws Exception {
        byte [] ivBytes = new byte[cipher.getBlockSize()];
        random.nextBytes(ivBytes);
        return new IvParameterSpec(ivBytes);
    }

}