Is Broken Cable Breaking Your Security?

Traditional methods of repairing a broken cable focus on restoring electrical connectivity and mechanical integrity, ignoring the electromagnetic aspects of it. Most of these repairing methods create a small monopole antenna as a byproduct which affects its electromagnetic compatibility (EMC). Switching activity in the transmitted signal through the wire creates an unintentional emission, called emanation, according to Maxwell's equations. This emanation is usually weak and suppressed to conform to EMC requirements. However, the monopole antenna of the repaired cable helps transmit it better, increasing the SNR of the emanation and extending its detection range significantly. This creates a serious security issue as emanations contain a significant correlation with the source signal and can be exploited for information extraction. In this work, the electromagnetic aspects of the broken cable repairing process have been explored in detail. We have applied the most commonly used cable repairing methods (twisting, soldering, and butt connector) to 3 types of widely used cables (USB, power, and HDMI cable) which are broken intentionally for experimental purposes. Collected data shows that the emanation SNR increases significantly due to the repairing process with -47 dBm power at a 20 cm distance. Although emanation power varies from cable to cable, it remains detectable even at >4 m distances. This strong emanation can penetrate through obstacles and remain detectable up to similar to 1 m distance through a 14 cm thick concrete wall. Along with exploring the vulnerability, a possible remedy, external metal shielding, has been explored in detail. This work exposes a new dimension of information leakage.