Generic Bootstrapping Architecture (GBA) is a technology that enables the authentication of a user. This authentication is possible if the user owns a valid identity on an HLR (Home Location Register) or on an HSS (Home Subscriber Server).
GBA is standardized at the 3GPP (http://www.3gpp.org/ftp/Specs/html-info/33220.htm). The user authentication is instantiated by a shared secret, one in the smartcard, for example a SIM card inside the mobile phone and the other is on the HLR/HSS.
GBA authenticates by making a network component challenge the smartcard and verify that the answer is the one predicted by the HLR/HSS.
Instead of asking the service provider to trust the BSF and relying on it for every authentication request, the BSF establishes a shared secret between the simcard card and the service provider. This shared secret is limited in time and for a specific domain.
