Index: src/org/apache/xml/security/utils/XMLUtils.java
===================================================================
--- src/org/apache/xml/security/utils/XMLUtils.java	(Revision 810928)
+++ src/org/apache/xml/security/utils/XMLUtils.java	(Arbeitskopie)
@@ -23,6 +23,7 @@
 import java.io.OutputStream;
 import java.security.AccessController;
 import java.security.PrivilegedAction;
+import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.Iterator;
@@ -227,7 +228,7 @@
 
 
    static  String dsPrefix=null;
-   static Map namePrefixes=new HashMap();
+   static private final Map namePrefixes=new HashMap();
    /**
     * Creates an Element in the XML Signature specification namespace.
     *
@@ -245,13 +246,15 @@
       if ((dsPrefix == null) || (dsPrefix.length() == 0)) {
          return doc.createElementNS(Constants.SignatureSpecNS, elementName);
       } 
-      String namePrefix=(String) namePrefixes.get(elementName);
+      String namePrefix=(String) Collections.unmodifiableMap(namePrefixes).get(elementName);
       if (namePrefix==null) {
     	  StringBuffer tag=new StringBuffer(dsPrefix);
     	  tag.append(':');
     	  tag.append(elementName);
     	  namePrefix=tag.toString();
-    	  namePrefixes.put(elementName,namePrefix);
+    	  synchronized (namePrefixes) {
+    		  namePrefixes.put(elementName,namePrefix);
+    	  }
       }
       return doc.createElementNS(Constants.SignatureSpecNS, namePrefix);
    }