Java BigInteger create random String

import java.math.BigInteger;
import java.security.SecureRandom;
import java.util.Random;

public class Main {

   public static void main(String[] args) {

      System.out.println(randomKey(5));
      System.out.println(randomKey(10));
   }/*w  w  w.  j a v  a 2s  . c om*/

   static final Random random = new SecureRandom();

   public static String randomKey(int length) { 
       return String.format("%"+length+"s", new BigInteger(length*5/*base 32,2^5*/, random) 
           .toString(32)).replace('\u0020',  '0'); 
   }
}