# Security Establishment in ADS-B by Format-Preserving Encryption and Blockchain Schemes
## 1 Introduction  
The ADS-B system broadcasts an aircraft's identification, position, velocity, and intent to other aircraft and ground stations. However, the introduction of these new technologies in the aviation industry has introduced new network weaknesses linked to their internet connection and the compatibility between systems [1]. Certain technological advancements, particularly the introduction of Software-Defined Radio (SDR) systems, enable attackers to utilize low-cost RF transmission and receiving. ADS-B transmits data in an open, unencrypted format to allow other aircraft to be informed of the sender's location. On the other hand, accessibility had been a safety requirement. Therefore, it lacks protection features, rendering it susceptible to a variety of assaults [2]. Researchers have shown that existing hardware and software can easily undermine the security of ADS-B systems [3]. Table 1 summarizes ADS-B's possible attack types, methods, and severity levels, and the requirements they impact most severely [4]. Therefore, the conventional ADS-B's data confidentiality, authenticity and integrity can be impacted by possible attacks. This problem might lead to severe consequences [4]. Although a number of solutions are offered to overcome the issue, either they were led to increase the ADS-B message length and reduce ADS-B air-traffic capacity, or the proposals were not implemented and examined in operational environments. Furthermore, some of the solutions impacted ADS-B performance, such as the degradation of ADS-B sensitivity. Additionally, cipher key exchange was not properly addressed. The proposed solutions are an imposed extra load to ADS-B messages by adding an authentication procedure, peer-to-peer communication, or a key data payload. These approaches lead to the reduction of ADS-B capacity and increased the system complexity and load. Very recent research was undertaken to deal with ADS-B security concerns, as referenced below:  
* Blockchain based ADS-B: The proposed model's objective was to deploy a blockchain model and benefit from its advantages to secure sensitive data [5; 6; 7; 8];
* Machine learning model: Various types of neural networks were offered to tackle message injection attacks [9; 10]; and
* Holistic framework: The solution used a cryptographic module based on a keyed-Hash Message Authentication Code (HMAC) to protect data integrity and authenticity [11];  
Detailed information of each method is provided in the literature review section. This research covers the design and implementation of a secured ADS-B (SADS-B) system using a software-defined radio (SDR) architecture. It explores the hardware architecture and configuration, presents a format-preserving encryption (FPE) scheme, and shows how blockchain technology can be used for leveraging ADS-B security and how BladeRF functions as a transceiver. The results achieved using this secured system are compatibility, achievability, and high security. Given the current, un-secured ADS-B systems, this work is motivated by the following issues:  
* Most of the recommended solutions are still in the experimental stage, being tested in controlled settings, and have yet to be implemented [4];
* Deploying FPE algorithms offers certified encryption for the protection of ADS-B messages without any changes in the message's length;
* While the use of FPE algorithms has been proposed as a security solution to benefit from its advantages [12], it has not yet been implemented and has not been challenged in operational environments such as implementation in SDR and experimentation in flight tests; and
* A permissioned blockchain system helps the operational environment not only to exchange the encryption key among nodes (ADS-B systems), but also to store important information. In this study, FPE algorithms' advantages are described and then implemented in both MATLAB Simulink and C++. Their evaluation was assessed under real flight data to obtain a comprehensive observation of the algorithm as well as of the ADS-B performance.