# Blockchain-Based Licensed Spectrum Fair Distribution Method towards 6G-Envisioned Communications
## 3 BEAST System Model
### System Process
The MNO's accountability and service commitments are etched into the very foundation of the system. The central idea of this design lies in its proactive deterrence against overbooking attacks. The stringent prerequisites for participation preclude any malicious MNO from exploiting the system. A would-be attacker, contemplating an overbooking gambit, is compelled to confront an impregnable barrier--the imperative of possessing adequate resources to substantiate their service claims. This serves as a self-enforcing safeguard, rendering overbooking attacks an unviable and ultimately futile endeavor. In conclusion, our multi-faceted approach, integrating blockchain technology, digital signatures and public key encryption, engenders a formidable fortress against overbooking attacks. The meticulous orchestration of these components not only thwarts potential attackers' attempts to manipulate the system but also fosters a holistic ecosystem where resource allocation remains equitable, reliable and immune to adversarial influence. This fortified defense stands resolute, poised to ensure the unimpeded and just access to spectrum resources for legitimate users. **Definition 2**. : _Security against repudiation attacks._Let us consider the presence of an adversary denoted as \(\mathcal{A}\), having control over a set of PB and PUs. We declare that \(\mathcal{A}\) has successfully executed a repudiation attack if it issued a repudiation against the fact that it has received an access to the demanded spectrum resources. We affirm that a system can robustly counteract \(\mathcal{A}\)'s repudiation attacks if the likelihood of their effective execution remains minimal and negligible. Our security approach integrates encryption through the Public Key Infrastructure (PKI) as a foundational shield, bolstering the trustworthiness of our system. By encapsulating posted authorization details beneath an impervious layer of cryptographic secrecy, we ensure that this information remains accessible solely to its intended recipient. This one-way encryption mechanism guarantees that only the targeted PBS/PU possesses the decryption key, preserving the sanctity of the data while enabling the authorized entity to unveil its contents effortlessly. The strategic fusion of public key encryption and the immutable blockchain architecture forms an unassailable bulwark against repudiation attempts. Dishonest parties, motivated to distort the truth by disavowing the services rendered with honest MNOs, find themselves thwarted by the cryptographic constraints. Any endeavor to deny the reception of services collides with an insurmountable cryptographic barrier, as the encrypted authorization data form an indelible proof imprinted upon the blockchain. The integration of digital signatures further seals this record, rendering it impervious to manipulation or falsification. In essence, our security framework not only assures the veracity of service transactions but also reinforces the credibility of MNO contributions. The cryptographic safeguards quell repudiation endeavors, establishing a steadfast assurance that dishonest PBS/PU entities cannot undermine the system's integrity by falsely repudiating legitimate services. This fortified protection, enshrined within the marriage of encryption and blockchain, ensures the steadfastness of service provisioning while championing the principle of accountability and transparency. #### 5.2.3 Censorship Resistance

BEAST is designed to provide robust censorship resistance, ensuring that both honest PBS and PUs can reliably obtain spectrum resources within a reasonable timeframe, free from the interference or obstruction of malicious participants or MNOs. This property is not only crucial for maintaining fairness but also for upholding the democratic principles of equal access to resources. To guarantee this vital aspect of BEAST, we strategically implemented and rigorously enforced a priority index mechanism.