Improve random distribution of generated stream IDs

Stream ID generation should be based on a strong random number generator,
should use a wider variety of characters than just hexadecimals, and
could be a bit larger for reduced chance of duplicates.

src/java/org/jivesoftware/openfire/spi/BasicStreamIDFactory.java

@@ -22,6 +22,9 @@ package org.jivesoftware.openfire.spi;
 
 import org.jivesoftware.openfire.StreamID;
 import org.jivesoftware.openfire.StreamIDFactory;
+
+import java.math.BigInteger;
+import java.security.SecureRandom;
 import java.util.Random;
 
 /**
@@ -33,13 +36,18 @@ import java.util.Random;
 public class BasicStreamIDFactory implements StreamIDFactory {
 
     /**
-     * The random number to use, someone with Java can predict stream IDs if they can guess the current seed *
+     * The maximum amount of characters in a stream ID that's generated by this implementation.
+     */
+    private static final int MAX_STRING_SIZE = 10;
+
+    /**
+     * The random number to use, someone with Java can predict stream IDs if they can guess the current seed
      */
-    Random random = new Random();
+    Random random = new SecureRandom();
 
     @Override
     public StreamID createStreamID() {
-        return new BasicStreamID(Integer.toHexString(random.nextInt()));
+        return new BasicStreamID(new BigInteger( MAX_STRING_SIZE * 5, random ).toString( 36 ));
     }
 
     public StreamID createStreamID(String name) {