  The number of active users of Wi-Fi Direct Device-to-Device file sharing
applications on Android has exceeded 1.8 billion. Wi-Fi Direct, also known as
Wi-Fi P2P, is commonly used for peer-to-peer, high-speed file transfer between
mobile devices, as well as a close proximity connection mode for wireless
cameras, network printers, TVs and other IoT and mobile devices. For its end
users, such type of direct file transfer does not incur cellular data charges.
However, despite the popularity of such applications, we observe that the
software vendors tend to prioritize the ease of user flow over the security in
their implementations, which leads to serious security flaws. We perform a
comprehensive security analysis in the context of security and usability and
report our findings in the form of 17 Common Vulnerabilities and Exposures
(CVE) which have been disclosed to the corresponding vendors. To address the
similar flaws at the early stage of the application design, we propose a joint
consideration of security and usability for such applications and their
protocols that can be visualized in form of a customised User Journey Map
(UJM).
