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