GCM mod of operation in Java BouncyCastle

    SecretKeySpec   key = new SecretKeySpec(keyBytes, "AES");
    IvParameterSpec ivSpec = new IvParameterSpec(ivBytes);
    Cipher          cipher = Cipher.getInstance("AES/GCM/NoPadding", "BC");
    byte[] block = new byte[1048576];
    int i;
    long st,et;

    cipher.init(Cipher.ENCRYPT_MODE, key, ivSpec);

    BufferedInputStream bIn=new BufferedInputStream(new ProgressMonitorInputStream(null,"Encrypting ...",new FileInputStream("input")));
    CipherInputStream       cIn = new CipherInputStream(bIn, cipher);
    BufferedOutputStream bOut=new BufferedOutputStream(new FileOutputStream("output.enc"));

    int ch;
    while ((i = cIn.read(block)) != -1) {
        bOut.write(block, 0, i);
    }
    cIn.close();
    bOut.close();

    Thread.sleep(5000);

    cipher.init(Cipher.DECRYPT_MODE, key, ivSpec);

    BufferedInputStream fis=new BufferedInputStream(new ProgressMonitorInputStream(null,"Decrypting ...",new FileInputStream("output.enc")));
    //FileInputStream fis=new FileInputStream("output.enc");
    //FileOutputStream ro=new FileOutputStream("regen.plain");
    BufferedOutputStream ro=new BufferedOutputStream(new FileOutputStream("regen.plain"));

    CipherInputStream dcIn = new CipherInputStream(fis, cipher);

    while ((i = dcIn.read(block)) != -1) {
        ro.write(block, 0, i);
    }

    dcIn.close();
    ro.close();