Some embodiments are directed to a cryptographic method for providing an electronic first device, an electronic second device and an electronic intermediary device, the cryptographic method establishing a cryptographically protected communication channel between the first device and the second device. The method comprises establishing a session identifier (SID) between the first device and the intermediary device. The first device sends the session identifier and a first key element to the second device over an out-of-band channel. The second device sends a registration message comprising the session identifier to the intermediary device. The first and derived at the first and second device.