Below code works fine to unzip the zipped file (.zip), not password protected one.

ParameterPage MyParam = tools.getParameterPage();
ClipboardPage WorkPage = tools.getPrimaryPage();
ClipboardProperty StreamList = WorkPage.getProperty("pyModeList");
ClipboardProperty NamesList = WorkPage.getProperty("pyNames");
String TemplateName = MyParam.getString("TemplateName");
java.util.zip.ZipEntry entry = null;
try {
java.util.zip.ZipInputStream zipStream = new java.util.zip.ZipInputStream(new java.io.ByteArrayInputStream(Base64Util.decodeToByteArray(tools.findPage("AttachmentPage").getString("pyAttachStream"))));
ArrayList<String> OutputList = new ArrayList<String>();
ArrayList<String> NameList = new ArrayList<String>();

  
  while((entry=zipStream.getNextEntry())!=null)
  {
   String entryName= entry.getName();
    if (entryName != null)
    {
       NameList.add(entryName); 
    }
   Boolean IsDirectory = false;
   if (entryName.endsWith(java.io.File.separator))
   {
     IsDirectory = true;
   }
   int bytesRead = -1 ;
   java.io.ByteArrayOutputStream outStream = new java.io.ByteArrayOutputStream();
    int len= (int) entry.getSize();
   byte[] tempBuffer = new byte[8192];
   while((bytesRead = zipStream.read(tempBuffer))!= -1)
   {
     outStream.write(tempBuffer,0,bytesRead);
   }
    
   if (outStream!=null)
   { 
    
    String EncodedOut = new com.pega.pegarules.pub.util.Base64Util().encodeToString( outStream.toByteArray());
     OutputList.add(EncodedOut);
   }
    
  }
  if(zipStream!=null)
  {
    zipStream.closeEntry();
    zipStream.close();
  }
for(int i=0; i<OutputList.size();i++)
{
  StreamList.add(OutputList.get(i));
  NamesList.add(NameList.get(i));
}

}
 catch (Exception ex)
 {oLog.infoForced("failed " + ex.getMessage());}