The conventional contract protocols in blockchains guarantee traceability and fairness by using centralized credible nodes. While the credible nodes are observed as conspired or dishonest ones with the signatory, the compromising of other nodes is performed. In the meantime, the leaking of sensitive information regarding the participant nodes creates a serious issue regarding the privacy and security of data access in the blockchain. The main intention of this paper is to design and develop a novel digital certificate-based data access in blockchain as a secured data access control scheme. The combination of blockchain and digital certificate technologies is accomplished here. As a new contribution, the adaptive key-based secured authentication protocol is developed. The well-performing algorithm, termed Elephant Herding Optimization (EHO) is used for adaptive key management. Finally, the experimental results show that the proposed scheme is superior in terms of execution time, encryption time, and decryption time.