# Protecting Data at Risk of Unintentional Electromagnetic Emanation: TEMPEST Profiling
## 3 Sources of Electromagnetic Leakage
### Radio Frequency Identification  
A deep understanding of how high-frequency (HF) radio signals move through a real circuit is imperative for RF design and analysis. The fact is that the components inside the circuit have tolerances and temperature dependencies, as well as parasitic elements; wires have resistance, inductance, and capacitance; and signals are susceptible to noise. Low-frequency (LF) systems, on the other hand, are less affected by non-ideal signals or component behavior. Radio-frequency identification is a wireless technology using EM or capacitive coupling in the RF spectrum to identify subjects or objects. RFID consists of an RFID tag (transponder), antenna, RFID transceiver, and software [82]. The tag contains a microchip with a unique ID number and an antenna. There are three types of RFID tags: (1) passive tags without a power source that receive power from radio signals sent by the RFID receiver and operate when the reader is near the tag; (2) battery tags that have built-in batteries for the logic chips but still require a RF signal from the reader to activate  
Figure 2: Frequency response of a PES (source [80]). and operate; and (3) active tags that use batteries and do not require reader power. RFID antennas are designed to operate at specific frequencies, depending on the application. The antenna is usually attached to the RFID reader and is available for tag attachment. Some handheld devices often have an attached antenna. An RFID reader is a hardware component that reads information from tags, connects them to a database, and transmits data. The specifications for low-frequency, high-frequency, ultra-high-frequency (UHF), and microwave RFID readers are shown in Table 5.  
The most important electrical parameter of RFID is tag sensitivity, which determines the maximum working distance. It should be noted that the specified reading distance is a theoretical open-space reading distance and may be reduced due to incorrect tag or reader usage. It can also be expanded due to multi-path propagation. UHF tags operate in the far-field region, which is significantly different from LF and HF technologies. RFID uses a specific application system depending on the service provider; local regulations on radio transmission dictate the frequencies for RFID operation. The software controls the RFID reader, initiates the scan, retrieves information from the tag, stores the data on a local computer, or sends it to cloud storage. The reading process begins by using the reader to access the information on the tag. RFID sends an RF signal using an antenna and receives a signal from a reader to activate the tag. An activated tag sends data back to the reader using the same antenna and inductive coupling method. Some tags have no security features, and some are protected and/or encrypted to improve security and privacy [10]. The attacks described by the authors of [12] are classified by network layers. Physical layer attacks are those that permanently or temporarily disable RFID tags. Network and transport layer attacks are based on how the RFID system communicates and transfers data between entities such as tags (spoofing, cloning), readers (eavesdropping, spoofing), and network protocols. Application layer attacks target information related to the application and the binding between the user and the RFID tag (unauthorized tag reading, tag modification, middleware attacks). There are also various multi-layered attacks, such as denial-of-service, covert channels, traffic analysis, replay attacks, and side-channel attacks [41]. In [83], the authors investigated a possible vulnerability of RFID to side-channel attacks. They demonstrated a non-invasive attack method involving information capturing from the EM field using the device during cryptographic operations. This technique requires placing near-field probes close to the chip to gather the relevant data. It turns out that more robust hardware or cryptographic computation techniques will improve protection against attacks.