# Security Establishment in ADS-B by Format-Preserving Encryption and Blockchain Schemes
## 2 Literature Review
Contrary to traditional packet ciphering, the reserved format encryption does not expand the data. The ciphertext keeps the format encryption in the same format as the plaintext, and thus this method minimizes encryption impact on the ciphertext length. Unlike the [PERSON] et al. [12] method that encrypts all of the ADS-B data, [PERSON] et al. [24] exploit the FPE scheme to encrypt only the ICAO24 Aircraft Address (AA) field of the ADS-B message. Thus, this method not only preserves the openness of the ADS-B system, but it also secures the aircraft's identity data against unauthorized users. It also protects aircraft against reconnaissance attacks. This approach provides confidentiality to some extent, as not all data is encrypted. [PERSON] [25] conducted a survey on the applicability of several types of FPE algorithms to apply ADS-B message encryption and examined their security and performance. Our research investigates the FPE method's security and performance based on real flight data, and it proposes a solution for how to apply the FPE scheme in a software-defined radio platform. There has been a strong trend recently among researchers and developers to use blockchain to increase avionics security. Blockchain has been exploited in several ways to address ADS-B security requirements. ATMChain is a blockchain-based framework presented by [PERSON] and [PERSON] [5] for the security of cyber-physical systems (CPS) in the Air Traffic Management (ATM) system. Their proposed model is based on an ATM-focused approach, in which the distributed blockchain network is used to construct the ATM-CPS security framework. ADS-B sensors compose one of the different modules, accompanied by satellites, radar units, and other devices. [PERSON] et al. suggest using the Hyperledger Fabric platform to deal with the security risks related to data link transmissions over ADS-B [8]. Their proposed ATM system consists of participants, such as various types of aircraft, which are divided into Zones A and B and are connected by a consensus blockchain network. However, the study is limited to the theoretical aspect. Another approach utilizing blockchain was investigated by [PERSON] et al. [6]. They propose a solution according to the aircraft's registration and their connection to the ground station. Their algorithm consists of three steps: first, a registered aircraft is considered as one transaction in the ledger that is authorized by ATC, then the aircraft is authenticated when the first GS sees it, and finally, control is transferred from one GS to another to perform the handover. [PERSON] et al. describe a blockchain-based public key infrastructure (PKI) solution to address ADS-B vulnerabilities [7]. Their proposed aviation blockchain infrastructure (ABI) serves as a link between technologies that are used in the air and those used on the ground. However, the limitations of real-time processing and the management of high numbers of transactions is not highlighted in PKI-based blockchain. These papers reveal the possibilities for using blockchain technology in ADS-B systems and provide direction and guidelines for our work. Although blockchain-related articles have proposed high-level security architectures for the entire ATM system or among nodes, they have not provided detailed information on how to implement it in operational environments.