Abstract: A low-assurance call on a mobile device to another device may be promoted to a high-assurance call using a user interface. The participants during the call do not need to hang up and start a new high-assurance call. A caller can swipe an icon up a slider, for example, and start a process of promoting the call. The initial low assurance call using SIP servers is terminated but this is transparent to the callers. Once the swipe is performed, a DTLS negotiation is performed between the devices. During this DTLS handshake, which is done directly between the device without involvement of the SIP servers, a key is exchanged. Only the calling devices are aware of this key which is used to encrypt media during the call. Screens on the calling devices show that the call is now high-assurance and security details of the call may also be displayed.