  Today, location-based applications and services such as friend finders and
geo-social networks are very popular. However, storing private position
information on third-party location servers leads to privacy problems. In our
previous work, we proposed a position sharing approach for secure management of
positions on non-trusted servers, which distributes position shares of limited
precision among servers of several providers. In this paper, we propose two
novel contributions to improve the original approach. First, we optimize the
placement of shares among servers by taking their trustworthiness into account.
Second, we optimize the location update protocols to minimize the number of
messages between mobile device and location servers.
