從光盤加載時無法解密XML文件

Question

我遇到以下問題。我寫了一個簡單的測試類，用java加密和解密XML文件。但是，當我嘗試解密從光盤加載文件時，出現以下錯誤：

Oct 04, 2017 5:41:49 PM com.sun.org.apache.xml.internal.security.encryption.XMLCipher doFinal 
SEVERE: Source element unexpectedly null... 
Exception in thread "main" java.lang.NullPointerException 
    at com.sun.org.apache.xml.internal.security.encryption.XMLCipher$Factory.newEncryptedData(XMLCipher.java:2190) 
    at com.sun.org.apache.xml.internal.security.encryption.XMLCipher.decryptToByteArray(XMLCipher.java:1677) 
    at com.sun.org.apache.xml.internal.security.encryption.XMLCipher.decryptElement(XMLCipher.java:1616) 
    at com.sun.org.apache.xml.internal.security.encryption.XMLCipher.doFinal(XMLCipher.java:936) 
    at EncryptionDecryption.decryptDocument(EncryptionDecryption.java:134) 
    at EncryptionDecryption.main(EncryptionDecryption.java:42) 

類：

import com.sun.org.apache.xml.internal.security.encryption.XMLCipher; 
import com.sun.org.apache.xml.internal.security.utils.EncryptionConstants; 
import org.w3c.dom.Document; 
import org.w3c.dom.Element; 

import javax.crypto.KeyGenerator; 
import javax.crypto.SecretKey; 
import javax.crypto.spec.SecretKeySpec; 
import javax.xml.parsers.DocumentBuilder; 
import javax.xml.parsers.DocumentBuilderFactory; 
import javax.xml.transform.OutputKeys; 
import javax.xml.transform.Transformer; 
import javax.xml.transform.TransformerFactory; 
import javax.xml.transform.dom.DOMSource; 
import javax.xml.transform.stream.StreamResult; 
import java.io.File; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import java.security.MessageDigest; 
import java.security.NoSuchAlgorithmException; 
import java.util.Arrays; 
import java.util.Base64; 

public class EncryptionDecryption { 


    public static void main(String[] args) throws Exception { 
     com.sun.org.apache.xml.internal.security.Init.init(); 
     byte[] key = ("i love stackoverflow").getBytes("UTF-8"); 
     MessageDigest sha = MessageDigest.getInstance("SHA-512"); 
     key = sha.digest(key); 
     key = Arrays.copyOf(key, 16); // use only first 128 bit 
     SecretKeySpec secretKeySpec = new SecretKeySpec(key, "AES"); 
     Document document = getDocument("classes.xml"); 

     Document encryptedDoc = encryptDocument(document, secretKeySpec, 
       XMLCipher.AES_256); 
     saveDocumentTo(encryptedDoc, "encrypted.xml"); 

     encryptedDoc = getDocument("encrypted.xml"); 

     Document decryptedDoc = decryptDocument(encryptedDoc, 
       secretKeySpec, XMLCipher.AES_256); 
     saveDocumentTo(decryptedDoc, "decrypted.xml"); 

    } 

    public static void saveSecretKey(SecretKey secretKey, String fileName) { 
     byte[] keyBytes = secretKey.getEncoded(); 
     File keyFile = new File(fileName); 
     FileOutputStream fOutStream = null; 
     try { 
      fOutStream = new FileOutputStream(keyFile); 
      fOutStream.write(keyBytes); 
     } catch (Exception e) { 
      e.printStackTrace(); 
     } finally { 
      if (fOutStream != null) { 
       try { 
        fOutStream.close(); 
       } catch (IOException e) { 
        e.printStackTrace(); 
       } 
      } 
     } 
    } 

    public static String keyToString(SecretKey secretKey) { 
    /* Get key in encoding format */ 
     byte encoded[] = secretKey.getEncoded(); 

    /* 
    * Encodes the specified byte array into a String using Base64 encoding 
    * scheme 
    */ 
     String encodedKey = Base64.getEncoder().encodeToString(encoded); 

     return encodedKey; 
    } 

    public static SecretKey getSecretKey(String algorithm) { 
     KeyGenerator keyGenerator = null; 
     try { 
      keyGenerator = KeyGenerator.getInstance(algorithm); 
     } catch (NoSuchAlgorithmException e) { 
      e.printStackTrace(); 
     } 
     return keyGenerator.generateKey(); 
    } 

    public static Document getDocument(String xmlFile) throws Exception { 
     /* Get the instance of BuilderFactory class. */ 
     DocumentBuilderFactory builder = DocumentBuilderFactory.newInstance(); 

     /* Instantiate DocumentBuilder object. */ 
     DocumentBuilder docBuilder = builder.newDocumentBuilder(); 

     /* Get the Document object */ 
     Document document = docBuilder.parse(xmlFile); 
     return document; 
    } 

    public static void saveDocumentTo(Document document, String fileName) 
      throws Exception { 
     TransformerFactory transformerFactory = TransformerFactory.newInstance(); 
     Transformer transformer = transformerFactory.newTransformer(); 
     transformer.setOutputProperty(OutputKeys.INDENT, "yes"); 
     transformer.setOutputProperty(OutputKeys.METHOD, "xml"); 
     transformer.setOutputProperty("{http://xml.apache.org/xslt}indent-amount", "4"); 
     DOMSource source = new DOMSource(document); 
     StreamResult result = new StreamResult(new File(fileName)); 
     transformer.transform(source, result); 
    } 

    public static Document encryptDocument(Document document, SecretKey secretKey, String algorithm) throws Exception { 
     /* Get Document root element */ 
     Element rootElement = document.getDocumentElement(); 
     String algorithmURI = algorithm; 
     XMLCipher xmlCipher = XMLCipher.getInstance(algorithmURI); 

     /* Initialize cipher with given secret key and operational mode */ 
     xmlCipher.init(XMLCipher.ENCRYPT_MODE, secretKey); 

     /* Process the contents of document */ 
     xmlCipher.doFinal(document, rootElement, true); 
     return document; 
    } 

    public static Document decryptDocument(Document document, SecretKey secretKey, String algorithm) throws Exception { 
     Element encryptedDataElement = (Element) document. 
       getElementsByTagNameNS(EncryptionConstants.EncryptionSpecNS, EncryptionConstants._TAG_ENCRYPTEDDATA).item(0); 
     XMLCipher xmlCipher = XMLCipher.getInstance(); 
     xmlCipher.init(XMLCipher.DECRYPT_MODE, secretKey); 
     xmlCipher.doFinal(document, encryptedDataElement); 
     return document; 
    } 

} 

當我註釋掉線40：

/*encryptedDoc = getDocument("encrypted.xml");*/ 

那麼問題不會出現。所以，這就像當我使用該程序時無需從盤載入運行過程中的XML文檔加密，則XMLCipher解密它成功地:)

Answer 1

你需要設置你DocumentBuilder是名稱空間感知的：

public static Document getDocument(String xmlFile) throws Exception { 
/* Get the instance of BuilderFactory class. */ 
    DocumentBuilderFactory builder = DocumentBuilderFactory.newInstance(); 
    builder.setNamespaceAware(true); 
    // ... 

無此設置庫在加密文檔時無法找到它存儲的元數據。