# Multibyte Electromagnetic Analysis Based on Particle Swarm Optimization Algorithm
## 1 Introduction  
With the rapid development of 5 th generation wireless systems (5G), more and more intelligent devices are connected to the Internet. At the same time, information security in communication process is being paid more and more attention. Many modern devices are used in people's lives, such as mobile phones, personal computers, smart TVs, sensor networks, cryptographic devices, and many other things, just as shown in Figure 1. It is well known that the electromagnetic (EM) signals will be radiated unintentionally when data are processing in these devices. These unintentional electromagnetic radiation could be used to recover the important information, even if they do not exceed the limits of the electromagnetic compatibility (EMC) regulation [1], which poses a threat to the information security. The U.S. National Security Agency has focused on the classified TEMPEST (Telecommunications Electronics Materials Protected from Emanating Spurious Transmissions) program for many years to prevent important information from leaking through this unintentional electromagnetic radiation.  
One of the most successful techniques for exploiting unintentional electromagnetic radiation is the electromagnetic analysis. A variety of research has been devoted to unintentional electromagnetic radiation in recent years. The screen content was reconstructed by analyzing the unintentional electromagnetic signal from video graphics adapter (VGA) connector when a document or a video was displayed on the liquid-crystal display (LCD) [2]. Remote visualization for screen displays of various mobile devices used in public spaces via electromagnetic waves was reproduced in [3]. The echo state network (ESN) was used to extract the characteristics of the collected electromagnetic signals from a mobile phone and then the support vector machine (SVM) method was used to pattern identifying the characteristics of signals in [4]. The printed image can be easily reconstructed using leaked electromagnetic radiation that came from a laser printer [5]. Leaked electromagnetic radiation from the cable of the USB keyboard was measured by using a field probe and recovery of the data was performed through it [6]. A display image was reconstructed based on the measured time changes in the electromagnetic radiation carrying the signals for drawing the display on touch screen devices such as tablets and smart phones [7]. The electromagnetic radiation signal observation method is also applicable to cryptographic devices. Secret signing keys of Elliptic Curve Digital Signature Algorithm (ECDSA) from iOS devices were extracted fully by unintentional electromagnetic emission [8]. A successful key recovery attack on commercially available contactless Radio Frequency Identification Devices (RFID) based on the Data Encryption Standard (DES) or Triple-DES (3 DES) cipher was shown in [9]. All of this research demonstrates that sensitive information can be recovered by unintentional electromagnetic radiation.  
In this paper, on the field of electromagnetic information security, we study the threats of information leakage through electromagnetic radiation that can be used to compromise commercial devices and equipment. The rest of the paper is organized as follows. The related works are introduced in Section 2. In Section 3, we introduce the basic knowledge used in our method, including the AES cryptographic algorithm, differential electromagnetic analysis, correlation electromagnetic analysis, and the PSO algorithm. In Section 3, we describe multibyte correlation electromagnetic analysis based on particle swarm optimization in detail. In Section 4, we present our experimental platform and show the experimental results. Finally, we conclude the paper in Section 5.