A core property of pervasive computing is smooth data flow with continuous 
availability across heterogeneous devices. In this context, the multitude of 
devices, the spontaneous nature of interactions, together with user mobility 
and frequent disconnections, pose novel challenges to designing secure 
systems. Furthermore, security related tasks such as setting up secure 
connections and access control lists, traditionally carried out by trained 
system administrators, must now be regularly performed by ordinary users. 
System designers should, therefore, pay special attention to the human factor. 
This doctoral research aims at defining usable security mechanisms that enable 
users to securely share information by easily establishing connections between 
devices and granting access rights to other parties. In this research, we 
apply usability principles to enable users to bootstrap secure ad-hoc 
connectivity and manage cross-device, fine-grained access control.