A free program for iPhone, by Blizzard Entertainment.

The Blizzard Authenticator app is the official app for two-factor authentication on Battle.net, the world’s most popular digital battle arena platform. Battle.net is a free-to-play platform where players can create their own games, build their own worlds, and compete with their friends and millions of other players around the globe in real-time multiplayer combat. The app lets you generate a unique authentication code for each player that you add to a game, which you can then enter on the player’s screen to confirm their identity. This helps protect your account from unauthorized access and helps prevent other players from taking your account information.