public String verify(JarFile jar, String... algorithms) throws IOException {
    if (algorithms == null || algorithms.length == 0) algorithms = new String[] {"MD5", "SHA"};
    else if (algorithms.length == 1 && algorithms[0].equals("-")) return null;

    try {
      Manifest m = jar.getManifest();
      if (m.getEntries().isEmpty()) return "No name sections";

      for (Enumeration<JarEntry> e = jar.entries(); e.hasMoreElements(); ) {
        JarEntry je = e.nextElement();
        if (MANIFEST_ENTRY.matcher(je.getName()).matches()) continue;

        Attributes nameSection = m.getAttributes(je.getName());
        if (nameSection == null) return "No name section for " + je.getName();

        for (String algorithm : algorithms) {
          try {
            MessageDigest md = MessageDigest.getInstance(algorithm);
            String expected = nameSection.getValue(algorithm + "-Digest");
            if (expected != null) {
              byte digest[] = Base64.decodeBase64(expected);
              copy(jar.getInputStream(je), md);
              if (!Arrays.equals(digest, md.digest()))
                return "Invalid digest for "
                    + je.getName()
                    + ", "
                    + expected
                    + " != "
                    + Base64.encodeBase64(md.digest());
            } else reporter.error("could not find digest for " + algorithm + "-Digest");
          } catch (NoSuchAlgorithmException nsae) {
            return "Missing digest algorithm " + algorithm;
          }
        }
      }
    } catch (Exception e) {
      return "Failed to verify due to exception: " + e.getMessage();
    }
    return null;
  }
 protected void definePackage(
     final File container, final String packageName, final Manifest manifest) {
   final String sectionName = packageName.replace('.', '/') + "/";
   String specificationTitle = null;
   String specificationVendor = null;
   String specificationVersion = null;
   String implementationTitle = null;
   String implementationVendor = null;
   String implementationVersion = null;
   String sealedString = null;
   URL sealBase = null;
   final Attributes sectionAttributes = manifest.getAttributes(sectionName);
   if (sectionAttributes != null) {
     specificationTitle = sectionAttributes.getValue(Attributes.Name.SPECIFICATION_TITLE);
     specificationVendor = sectionAttributes.getValue(Attributes.Name.SPECIFICATION_VENDOR);
     specificationVersion = sectionAttributes.getValue(Attributes.Name.SPECIFICATION_VERSION);
     implementationTitle = sectionAttributes.getValue(Attributes.Name.IMPLEMENTATION_TITLE);
     implementationVendor = sectionAttributes.getValue(Attributes.Name.IMPLEMENTATION_VENDOR);
     implementationVersion = sectionAttributes.getValue(Attributes.Name.IMPLEMENTATION_VERSION);
     sealedString = sectionAttributes.getValue(Attributes.Name.SEALED);
   }
   final Attributes mainAttributes = manifest.getMainAttributes();
   if (mainAttributes != null) {
     if (specificationTitle == null) {
       specificationTitle = mainAttributes.getValue(Attributes.Name.SPECIFICATION_TITLE);
     }
     if (specificationVendor == null) {
       specificationVendor = mainAttributes.getValue(Attributes.Name.SPECIFICATION_VENDOR);
     }
     if (specificationVersion == null) {
       specificationVersion = mainAttributes.getValue(Attributes.Name.SPECIFICATION_VERSION);
     }
     if (implementationTitle == null) {
       implementationTitle = mainAttributes.getValue(Attributes.Name.IMPLEMENTATION_TITLE);
     }
     if (implementationVendor == null) {
       implementationVendor = mainAttributes.getValue(Attributes.Name.IMPLEMENTATION_VENDOR);
     }
     if (implementationVersion == null) {
       implementationVersion = mainAttributes.getValue(Attributes.Name.IMPLEMENTATION_VERSION);
     }
     if (sealedString == null) {
       sealedString = mainAttributes.getValue(Attributes.Name.SEALED);
     }
   }
   if (sealedString != null && sealedString.equalsIgnoreCase("true")) {
     try {
       sealBase = new URL(FileUtils.getFileUtils().toURI(container.getAbsolutePath()));
     } catch (MalformedURLException ex) {
     }
   }
   this.definePackage(
       packageName,
       specificationTitle,
       specificationVersion,
       specificationVendor,
       implementationTitle,
       implementationVersion,
       implementationVendor,
       sealBase);
 }