// Fast convert a byte array to a hex string
// with possible leading zero.

public static String toHexString ( byte[] b )
   {
   StringBuffer sb = new StringBuffer( b.length * 2 );
   for ( int i=0; i<b.length; i++ )
      {
      // look up high nibble char
      sb.append( hexChar [( b[i] & 0xf0 ) >>> 4] );

      // look up low nibble char
      sb.append( hexChar [b[i] & 0x0f] );
      }
   return sb.toString();
   }

// table to convert a nibble to a hex char.
static char[] hexChar = {
   '0' , '1' , '2' , '3' ,
   '4' , '5' , '6' , '7' ,
   '8' , '9' , 'a' , 'b' ,
   'c' , 'd' , 'e' , 'f'};