# PowerBridge: Covert Air-Gap Exfiltration/Infiltration via Smart Plug
## 3 Related Work  
Covert channels can generally be classified into two types: the first type involves network-based methods, such as modifying TCP and UDP packet structures or exploiting packet time delays and other characteristics. The second type encompasses air-gap channels that leverage the physical properties of devices, including sound, light, magnetism, and heat. In scenarios where sensitive and critical computers are prohibited from connecting to external networks, establishing the first type of air-gap channel becomes infeasible; hence, researchers focus on exploring the possibilities of establishing the second type. Figure 5: Places with hidden risks. (**a**) Plug in conference room; (**b**) plug in hotel. Figure 6: Physical image of smart meter. Air-gap channels can be established by transmitting signals such as electromagnetic, acoustic, optical, and power line signals. The utilization of electromagnetic signals to establish air-gap channels has a long-standing history, yet researchers continue to explore novel methodologies in this field. In 2020, [PERSON], [PERSON] et al. demonstrated BitJabber [23], the utilization of memory access for modulating electromagnetic (EM) signals generated by DRAM clocks to construct channels with a bandwidth reaching up to 300,000 bps and the capability to penetrate concrete walls up to 15 cm thick. In 2022, [PERSON] et al. developed AIR-FI [24], which enables signal transmission exclusively through a memory bus and the interception of these signals via devices equipped with WiFi capabilities, such as smartphones, laptops, and IoT devices. In 2024, [PERSON] et al. discovered RAMBO [25], which generates radio signals from the memory bus (RAM) and employs software-defined radio (SDR) hardware along with readily available antennas for signal reception at communication speeds of up to 1000 bit/s. Vibration and sound waves offer alternative approaches. In 2021, [PERSON] successfully addressed the air-gap channel by utilizing vibration, enabling Air-ViBeR [26] to adjust its internal fan speed through acceleration sensors in smartphones for signal reception. In 2019, [PERSON] et al. examined the technique of signal injection using mobile phone microphones [27]. In 2022, [PERSON] et al. demonstrated InkFiltra [28], a method employing malicious software to generate specific sound signals during computer printing that can be captured and decoded by nearby acoustic recording devices like smartphones; it achieves a communication distance of up to 4 m with an average bit rate of approximately 0.5 bps. Optics offers an alternative approach. In 2021, [PERSON] et al. demonstrated Laser-Shark [29], a technique that utilizes modulated laser aiming devices to operate LEDs on the CPU GPIO interface and capture their flicker, enabling long-distance (25 m), bidirectional air-gap communication channels. In 2022, [PERSON] et al. presented ETHERLED [30], which manipulates the flashing and alternating colors of Network Interface Controller (NIC) LEDs through malicious software to transmit signals. In 2023, [PERSON] et al. introduced CD-BLink [31], as a method for extracting data from an air-gap network by modulating the read and write LEDs on an optical drive. In 2018, [PERSON] et al. demonstrated that PowerHammer [7] effectively regulates system power consumption by deliberately adjusting CPU utilization. The data are modulated, encoded, and transmitted based on current fluctuations, which are then propagated through power lines. In 2023, [PERSON] et al. further presented POWER-SUPPLAY [32], a technique utilizing a computer's power unit (PSU) to generate sound covertly and transmit it to nearby receivers like smartphones. We primarily investigated air-gap channels capable of breaching air-gap isolation and presented the channel design, process, analysis, and evaluation. Table 1 enumerates the prevalent existing air-gap communication channels. The PowerBridge air-gap channel we propose distinguishes itself from previous research in the following aspects:  
Robust universality.