Best method for encrypting/decrypting large XML files ( 100MB)

Question

I am in need of encrypting XML for large part files that can get upwards of 100Mb+.
I found some articles and code, but the only example I was successful in getting to work used XMLCipher, which takes a Document, parses it, and then encrypts it.
Obviously, 100Mb files do not cooperate well with DOM, so I want to find a better method for encryption/decryption of these files.
I found some articles using a CipherInputStream and CipherOutputStreams, but am not clear if this is the way to go and if this will avoid memory errors.
import java.io.*;
import java.security.spec.AlgorithmParameterSpec;
import javax.crypto.*;
import javax.crypto.spec.IvParameterSpec;
public class DesEncrypter {
    Cipher ecipher;
    Cipher dcipher;
    public DesEncrypter(SecretKey key) {
        // Create an 8-byte initialization vector
        byte[] iv = new byte[]{
            (byte)0x8E, 0x12, 0x39, (byte)0x9C,
            0x07, 0x72, 0x6F, 0x5A
        AlgorithmParameterSpec paramSpec = new IvParameterSpec(iv);
        try {
            ecipher = Cipher.getInstance("DES/CBC/PKCS5Padding");
            dcipher = Cipher.getInstance("DES/CBC/PKCS5Padding");
            // CBC requires an initialization vector
            ecipher.init(Cipher.ENCRYPT_MODE, key, paramSpec);
            dcipher.init(Cipher.DECRYPT_MODE, key, paramSpec);
        } catch (java.security.InvalidAlgorithmParameterException e) {
        } catch (javax.crypto.NoSuchPaddingException e) {
        } catch (java.security.NoSuchAlgorithmException e) {
        } catch (java.security.InvalidKeyException e) {
    // Buffer used to transport the bytes from one stream to another
    byte[] buf = new byte[1024];
    public void encrypt(InputStream in, OutputStream out) {
        try {
            // Bytes written to out will be encrypted
            out = new CipherOutputStream(out, ecipher);
            // Read in the cleartext bytes and write to out to encrypt
            int numRead = 0;
            while ((numRead = in.read(buf)) >= 0) {
                out.write(buf, 0, numRead);
            out.close();
        } catch (java.io.IOException e) {
    public void decrypt(InputStream in, OutputStream out) {
        try {
            // Bytes read from in will be decrypted
            in = new CipherInputStream(in, dcipher);
            // Read in the decrypted bytes and write the cleartext to out
            int numRead = 0;
            while ((numRead = in.read(buf)) >= 0) {
                out.write(buf, 0, numRead);
            out.close();
        } catch (java.io.IOException e) {
}This looks like it might fit, but there is one more twist, I am using a persistence manager and xml encoding to accomplish that, so I am not sure how (where) to implement this method without affecting persistence.
Any guidance on what would work best in this situation would be appreciated.
Regards,
vbplayr2000

Answer 1

I can give some general guidelines that might help, having done much similar work:
You have 2 different issues, at least from my reading of your problem:
1) How to deal with large XML docs that most parsers will not handle without memory issues
2) Where to hide or "black box" the encrypt/decrypt routines
#1: Check into XPP3/XMLPull. Yes, it's different that the other XML parsers you are used to using, and more work is involved, but it is blazing fast and can be used to parse a stream as it is being read. You can populate beans and process as needed since there is really not much "inversion of control" involved compared to parsers that go on to finish the entire document or load it all into memory.
#2: Extend Serializable and write your own readObject/writeObject methods. Place the encrypt/decrypt in there as appropriate. That will "hide" the implementation and should be what any persistence manager can deal with.
Regards,
antarti