The digital transformation of higher education systems is accompanied by the rapid adoption of electronic diplomas, certificates, and micro-credentials. However, centralized models for storing and verifying educational records remain vulnerable to document forgery, unauthorized data modification, personal data breaches, and cyberattacks. The growing global mobility of learners and the integration of international educational platforms further increase the demand for a secure, scalable, and cryptographically protected trust infrastructure. This study proposes a formalized security and reliability model for a decentralized educational certificate system based on a permissioned blockchain architecture. The proposed framework integrates distributed consensus mechanisms (PBFT), cryptographic immutability techniques (hash functions, Merkle trees, and digital signatures), formal threat modeling (STRIDE), and a probabilistic network reliability model. The research presents mathematical formulations for evaluating fault tolerance, Byzantine resilience coefficients, and cryptographic data integrity levels. Using Python-based simulation, the study analyzes the impact of the proportion of Byzantine nodes on consensus stability, network throughput (TPS), certificate compromise probability, and resistance to Sybil and replay attacks. The results demonstrate that the proposed architecture provides a high level of security provided that the proportion of malicious nodes does not exceed the critical threshold of one-third of the total validator nodes, which is consistent with the theoretical principles of Byzantine Fault Tolerance (BFT). The findings confirm the applicability of the proposed model for national and transnational educational ecosystems and provide a foundation for the future standardization of digital educational certificates. Overall, the results demonstrate strong consistency between theoretical BFT principles and empirical simulation data, confirming that blockchain-based decentralized architectures can serve as reliable, scalable, and cryptographically secure infrastructures for digital academic credentials in the era of global digital transformation of higher education.
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