PHP poor man's crypt

function encrypt( $string )
{
  $key = 'BXcfTYewQ';
  $result = '';
  for( $i = 1; $i <= strlen( $string ); $i++ )
  {
    $char = substr( $string, $i - 1, 1 );
    $keychar = substr( $key, ( $i % strlen( $key ) ) - 1, 1 );
    $char = chr( ord( $char ) + ord( $keychar ) );
    $result .= $char;
  }
  return $result;
}
 
function decrypt( $string )
{
  $key = 'BXcfTYewQ';
  $result = '';
  for( $i = 1; $i <= strlen( $string ); $i++ )
  {
    $char = substr( $string, $i - 1, 1 );
    $keychar = substr( $key, ( $i % strlen( $key ) ) - 1, 1);
    $char = chr( ord( $char ) - ord( $keychar ) );
    $result .= $char;
  }
  return $result;
}