Methods, systems, and computer programs for trusted communication among mobile devices are described. In some aspects, an authentication value is generated at a first mobile device based on a message and a shared secret value stored on the first mobile device. In response to detecting proximity of a second mobile device, the message and the authentication value are wirelessly transmitted from the first mobile device to the second mobile device. In some implementations, the message and the authentication value can be wirelessly transmitted by a proximity-activated wireless interface, such as, for example, a Near Field Communication (NFC) interface.