When people are introduced to each other, exchanging contact information happens either via smartphone interactions or via more traditional business cards. Crowded social events make it more challenging to keep track of all the new contacts. We introduce HandshakAR, a novel wearable augmented reality application that enables effortless sharing of digital information. When two people share the same greeting gesture (e.g., shaking hands) and are physically close to each other, their contact information is effortlessly exchanged. There is no instrumentation in the environment required, our approach works on the users' wearable devices. Physical proximity is detected via inaudible acoustic signals, hand gestures are recognized from motion sensors, the communication between devices is handled over Bluetooth, and contact information is displayed on smartglasses. We describe the concept, the design, and an implementation of our system on unmodifed wearable devices.