A method, performed by a User Equipment device (UE), for obtaining a key for direct communication with a device over an air interface, wherein the UE has previously acquired a transaction identifier received from a Bootstrapping Server Function (BSF), in a Generic Bootstrapping Architecture (GBA), procedure, is provided. The method comprises storing the transaction identifier, sending the transaction identifier to the device and requesting key generation for direct communication with the device. If the transaction identifier is invalid, the method further comprises receiving from the device a device identifier and key generation information, deriving a session shared key from at least the key generation information, and deriving a direct communication key from at least the session shared key and the device identifier.