``Pairing'' is referred to as the operation of achieving authenticated key agreement between two human-operated devices over a short-range wireless communication channel (such as Bluetooth, WiFi). The devices are ad hoc in nature, i.e., they can neither be assumed to have a prior context (or pre-shared secrets) with each other nor do they share a common trusted on- or off-line authority. However, the devices can generally be connected using auxiliary physical channel(s) (such as audio, visual, etc.) that can be authenticated by the device user(s), and thus form the basis for pairing.

Recent research yielded a number of pairing schemes. Unfortunately, none of these schemes are applicable to most common pairing scenarios, such as pairing of a WiFi laptop and an access point, a Bluetooth keyboard and a desktop, etc. In such scenarios, the fundamental problem lies in the establishment of the physical channel(s) -- both devices do not have good transmitters (e.g., speakers, displays, etc.) and only at most one device has a receiver (e.g., a microphone, a camera, etc.). Even in scenarios where the prior schemes do apply, their usability is either poor or questionable.

In this paper, we first point out a security weakness in a recent pairing scheme proposed to pair two devices, only one of which has a receiver (e.g., a WiFi cell phone and an access point). We then present a new pairing scheme that is universally applicable to any pair of devices, supporting all possible pairing scenarios including the most common ones. Our scheme does not require devices to have good transmitters or any receivers, and is based upon the device user(s) comparing short and simple synchronized audiovisual patterns, such as ``beeping'' and ``blinking''.