MIPair: Exploiting Magnetic Induction for Laptop-Phone Pairing

Transferring important files, photos, and other sensitive data between laptops and smartphones has become a routine necessity in daily life. Device pairing acts as the most fundamental need to secure the communication channel between two unconnected devices. Traditional pairing methods leveraging PINs or QR codes require tedious human efforts in the pairing procedures to establish a shared communication key. Nevertheless, these designs are vulnerable to shoulder-surfing attacks in which attackers might record and replay the pairing credentials. It is preferred to have more intuitive pairing designs that minimize users’ overhead in the pairing process while providing secure keys for communication purposes. In this paper, we propose MIPair for laptop-phone pairing by leveraging magnetic induction (MI) signals. MIPair is based on a key observation that changes in the CPU workload of a device cause variations in internal current, thereby inducing changes in surrounding magnetic fields. Moreover, the trends of MI signal variations are highly correlated with CPU workload trends. Thus, users simply need to place a smartphone on the keyboard of a laptop. By randomly altering the workload of the laptop through a stimulation program, the smartphone can capture MI signals with similar changing trends, thereby converting them into similar bit sequences that form the basis of a symmetric key. We propose essential techniques to overcome challenges such as time asynchronization between two devices, unfixed state transition time in MI signal, and shared key distribution from the two similar bit sequences. Our real-world experiments demonstrate reliable pairing as well as robustness against common attacks and high randomness of the generated keys. When generating a 128-bit key, MIPair achieves a successful pairing rate as high as 98% and a usable pairing time of 8.35 seconds.