POI Docx De-/Encryption

package org.apache.poi.xslf.usermodel;

import static org.junit.Assert.assertTrue;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Arrays;

import org.apache.poi.POIDataSamples;
import org.apache.poi.poifs.common.POIFSConstants;
import org.apache.poi.poifs.crypt.Decryptor;
import org.apache.poi.poifs.crypt.EncryptionInfo;
import org.apache.poi.poifs.crypt.EncryptionMode;
import org.apache.poi.poifs.crypt.Encryptor;
import org.apache.poi.poifs.filesystem.NPOIFSFileSystem;
import org.apache.poi.poifs.filesystem.POIFSFileSystem;
import org.apache.poi.xwpf.usermodel.XWPFDocument;
import org.junit.Test;

public class TestMisc {
    @Test
    public void protectedRewrite() throws Exception {
        File docs[] = {
            POIDataSamples.getDocumentInstance().getFile("52288.docx"),
            POIDataSamples.getPOIFSInstance().getFile("protected_agile.docx"),
        };

        for (File doc : docs) {
            if (isEncrypted(doc)) {
                NPOIFSFileSystem fs = new NPOIFSFileSystem(doc, true);

                // decrypt the protected file - in this case it was encrypted with the default password
                EncryptionInfo encInfo = new EncryptionInfo(fs);
                Decryptor d = encInfo.getDecryptor();
                boolean b = d.verifyPassword(Decryptor.DEFAULT_PASSWORD);
                assertTrue(b);

                // do some strange things with it
                XWPFDocument docx = new XWPFDocument(d.getDataStream(fs));
                docx.getParagraphArray(0).insertNewRun(0).setText("Ajeet was here! All your base are belong to us!");
                docx.getParagraphArray(0).insertNewRun(1).addBreak();
                // in-place write of the original npoifs doesn't work, so using a new POIFS for now
                fs.close();

                // and encrypt it again
                POIFSFileSystem fs2 = new POIFSFileSystem();
                encInfo = new EncryptionInfo(fs2, EncryptionMode.agile);
                Encryptor e = encInfo.getEncryptor();
                e.confirmPassword("AYBABTU");
                docx.write(e.getDataStream(fs2));
                FileOutputStream fos = new FileOutputStream(new File(doc.getName()));
                fs2.writeFilesystem(fos);
                fos.close();
            } else {
                System.out.println(doc.getName()+" is without encryption");
            }
        }
    }

    public static boolean isEncrypted(File file) throws IOException {
        FileInputStream fis = new FileInputStream(file);
        byte buf[] = new byte[4];
        fis.read(buf);
        fis.close();

        if (Arrays.equals(buf, POIFSConstants.OOXML_FILE_HEADER)) {
            // plain ooxml
            return false;
        }

        NPOIFSFileSystem poifs = new NPOIFSFileSystem(file);
        boolean hasEncInf = poifs.getRoot().hasEntry("EncryptionInfo");
        poifs.close();

        return hasEncInf;
    }
}