Sangwon Hyun’s research while affiliated with Myongji University and other places

Web servers typically use data compression and encryption to optimize data transmission and protect user privacy. However, compression can inadvertently introduce vulnerabilities to compression side channel attacks (CSCA), which exploit the relationship between data redundancy and compression size to infer sensitive information. In this paper, we introduce Prexion, a novel compression system designed to counter CSCA while maintaining high compression efficiency. Prexion leverages a probabilistic mechanism to selectively include or exclude overlapping sequences in web page data during compression, making it difficult for attackers to exploit patterns in compressed sizes. This approach preserves the benefits of compression without compromising security. Through extensive experiments with real-world web pages, Prexion demonstrates superior performance, achieving up to 4.9 times better compression ratios than the current state-of-the-art solution, Debreach, for web pages with significant amounts of sensitive data. Furthermore, Prexion ensures robust security, with attack success rates consistently below 5% under recommended configurations.

To enhance the performance of web services, web servers often compress data to be delivered. Unfortunately, the data compression technique has also introduced a side effect called compression side-channel attacks (CSCA). CSCA allows eavesdroppers to unveil secret strings included in the encrypted traffic by observing the length of data. A promising defense technique called Debreach was recently proposed to mitigate CSCA by excluding all secret data in a web page during the compression process. Although Debreach has proven to be safe against CSCA and outperforms other approaches, the exclusion of all secret data from compression eventually resulted in a decreased compression efficiency. In this paper, we present a highly efficient CSCA mitigation system called “Mutexion” ( Mut ually ex clusive compress ion ) which allows us to fully take advantage of compression over an entire web page, including secret data. The key idea behind Mutexion is to fully take advantage of all the matching subsequences within a web page except only for those between secret data and user-controlled data (potentially controlled by an attacker) during the compression process. This approach of Mutexion effectively prevents side-channel leaks of secret data under CSCA misusing user-controlled data in a web page while minimizing the degradation in compression efficiency. It is required for our compressor to trace both secret data and user-controlled data in its compression process of web pages. To meet this requirement, we provide techniques to enable automated annotation of secret and user-controlled data in web pages. We implemented Mutexion as a fully working system to test live web pages and evaluated its performance with respect to security and compression efficiency. Our evaluation results demonstrated that Mutexion effectively prevents CSCA and also achieves almost the same compression ratio as the original zlib, which is vulnerable to CSCA, with a slight increase (0.032 milliseconds (7.9%) on average) in execution time.

Extensive use of unmanned aerial vehicles (commonly referred to as a “drone”) has posed security and safety challenges. To mitigate security threats caused by flights of unauthorized drones, we present a framework called SENTINEL (Secure and Efficient autheNTIcation for uNmanned aErial vehicLes) under the Internet of Drones (IoD) infrastructure. SENTINEL is specifically designed to minimize the computational and traffic overheads caused by certificate exchanges and asymmetric cryptography computations that are typically required for authentication protocols. SENTINEL initially generates a flight session key for a drone having a flight plan and registers the flight session key and its flight plan into a centralized database that can be accessed by ground stations. The registered flight session key is then used as the message authentication code key to authenticate the drone by any ground station while the drone is flying. To demonstrate the feasibility of the proposed scheme, we implemented a prototype of SENTINEL with ECDSA, PBKDF2 and HMAC-SHA256. The experiment results demonstrated that the average execution time of the authentication protocol in SENTINEL was about 3.1 times faster than the “TLS for IoT” protocol. We also formally proved the security of SENTINEL using ProVerif that is an automatic cryptographic protocol verifier.

As the number of network devices is increasing and they are highly connected, network attacks have become more complex and varied. To mitigate these attacks, multiple types of network security equipment are used in combination, requiring considerable security knowledge of each type of network security equipment. Also, the deployment of network security equipment requires considerable cost and time. To solve these problems, this article proposes an IBCS based on automation and virtualization. IBCS provides not only an automated, virtualized security system for security service providers, but also easy, quick, and flexible cloud-based security services for security service consumers based on their intents. Finally, this article demonstrates the feasibility of IBCS with a prototype in a real network environments.

As the number of controllers and devices increases in Industrial Internet of Things (IIoT) applications, it is essential to provide a secure and usable user authentication system for human operators who have to manage tens or hundreds of controllers and devices with his/her password. In this paper, we propose a formally verified certificate-based authentication system using a secondary network device for such IIoT applications. In the proposed system, a user’s sign key is encrypted with a secret key that can be computed with his/her password and a secret parameter in a secondary device to securely protect the sign key. To demonstrate the feasibility of the proposed system, we implemented a prototype with standard cryptographic algorithms (AES-256, RSA-3072, and ECDSA-256). The experiment results demonstrated that the execution time overhead of the sign key recovery process was 0.039 and 0.073 s, respectively, for RSA-3072 and ECDSA-256, which was marginal compared with the total execution time (0.383 s for RSA-3072 and 0.319 s for ECDSA-256) of the conventional system. We also verified the security of the proposed protocol using a formal verification tool called ProVerif.

Decompilation is frequently used to analyze binary programs. In Android, however, decompilers all perform differently with varying apps due to their own characteristics. Obviously, there is no universal solution in all conditions. Based on this observation, we present a practical Android app decompilation system (called Kerberoid) that automatically stitches the results from multiple decompilers together to maximize the coverage and the accuracy of decompiled codes. We evaluate the performance of Kerberoid with 151 Android apps in which their corresponding source codes are publicly available. Kerberoid fully recovered all functions for 17% of the apps tested and gained a similarity score over 50% for 40% of the apps tested, increased by 7% and 9%, respectively, compared with the best existing decompiler.

Voice assistant is an application that helps users to interact with their devices using voice commands in a more intuitive and natural manner. Recently, many voice assistant applications have been popularly deployed on smartphones and voice-controlled smart speakers. However, the threat and security of those applications have been examined only in very few studies. In this paper, we identify potential threats to voice assistant applications and assess the risk of those threats using the STRIDE and DREAD models. Our threat modeling demonstrates that generic voice assistants can potentially have 16 security threats. To mitigate the identified threats, we also discuss several defense strategies.

Instant messaging applications store users' personal data (e.g., user profile, chat messages, photos and video clips). Because those data typically include privacy sensitive information, most instant messaging applications are trying to protect the stored data in an encrypted form so that the authorized messaging application itself can only access the data. In this paper, we analyzed the locations and file formats of personal data files in three instant messaging applications (KakaoTalk, NateOn, and QQ)which are the most popularly used in China and South Korea. We particularly examined the encryption and decryption procedures for internal databases in those messaging applications through reverse-engineering. Our analysis results demonstrate how the database files of those instant messaging applications are stored and encrypted. Moreover, in the cases of KakaoTalk and NateOn applications, we found that their encrypted database files can successfully be recovered without requiring user password. We also found that QQ messenger stores the encryption key for the database files into an external server. This implementation may raise another privacy concern because users’ personal data can be freely accessed by the service provider without user consent.

Establishing secret command and control (C&C) channels from attackers is important in malware design. This paper presents design and analysis of malware architecture exploiting push notification services as C&C channels. The key feature of the push notification-based malware design is remote triggering , which allows attackers to trigger and execute their malware by push notifications. The use of push notification services as covert channels makes it difficult to distinguish this type of malware from other normal applications also using the same services. We implemented a backdoor prototype on Android devices as a proof-of-concept of the push notification-based malware and evaluated its stealthiness and feasibility. Our malware implementation effectively evaded the existing malware analysis tools such as 55 antimalware scanners from VirusTotal and SandDroid. In addition, our backdoor implementation successfully cracked about 98% of all the tested unlock secrets (either PINs or unlock patterns) in 5 seconds with only a fraction (less than 0.01%) of the total power consumption of the device. Finally, we proposed several defense strategies to mitigate push notification-based malware by carefully analyzing its attack process. Our defense strategies include filtering subscription requests for push notifications from suspicious applications, providing centralized management and access control of registration tokens of applications, detecting malicious push messages by analyzing message contents and characteristic patterns demonstrated by malicious push messages, and detecting malware by analyzing the behaviors of applications after receiving push messages.

Content-Centric Networking (CCN) is considered as a promising alternative to traditional IP-based networking for vehicle-to-everything communication environments. In general, CCN packets must be fragmented and reassembled based on the Maximum Transmission Unit (MTU) size of the content delivery path. It is thus challenging to securely protect fragmented packets against attackers who intentionally inject malicious fragments to disrupt normal services on CCN-based vehicular networks. This paper presents a new secure content fragmentation method that is resistant to Denial-of-Service (DoS) attacks in CCN-based vehicular networks. Our approach guarantees the authenticity of each fragment through the immediate fragment verification at interim nodes on the routing path. Our experiment results demonstrate that the proposed approach provides much stronger security than the existing approach named FIGOA, without imposing a significant overhead in the process. The proposed method achieves a high immediate verification probability of 98.2% on average, which is 52% higher than that of FIGOA, while requiring only 14% more fragments than FIGOA.