By Joseph Menn SAN FRANCISCO (Reuters) – Public concerns about the U.S. governments secretive surveillance programs exposed by Edward Snowden have spawned a slew of encryption products and privacy services that aim to make electronic spying more difficult. Two products brought out in the past five weeks illustrate the rapid development of the new marketplace: Blackphone, a handset which started shipping on June 30 for $629, and Signal, a free app that appeared on the iPhone app store last week. They are among an array of offerings to emerge since Snowden, a former National Security Agency contractor, last year leaked documents that showed the U.S. government harvested enormous amounts of data from the likes of Google Inc, Yahoo Inc, Microsoft Corp, ATT Inc and Verizon Communications Inc. Though they have different business philosophies, target markets and tactical approaches, the companies behind Blackphone and Signal share an underlying encryption technique, world-class cryptographers, and an anti-government stance.