Many systems have been built for transactions without a central manager by introducing blockchain in various fields such as industry, public sector, and trading economy. The blockchain system is also contributing to the advancement of technology to enable reliable transactions in distributed networks like P2P or D2D. Consensus algorithm for each operating environment is used to verify whether a transaction is valid. Transactions are verified generally with Proof-of-work (PoW) in public blockchain and Practice Byzantine Fault Tolerance (PBFT) in private blockchain. The PBFT is only available to a group of limited participants and is used for small groups. However, these small groups can be compromised by the collusion of malicious users, making it impossible to trade or forge. In addition, the blockchain does not define any security structure on users, devices, transaction history accessibility, etc., which causes issues with system permission. Therefore, this paper analyzes the problem of the conventional blockchain in terms of participant-collusion, authentication, and confidentiality, and proposes a Randomly Elected Blockchain (REBC) to solve each problem. In the first participant-collusion, the private blockchain enables the system to operate without any cost for verification. Thereby solving the problem of grouping nodes for malicious collusion, the proposed mechanism is to randomly elect the nodes in the unit group, and then conduct consensus algorithms. Besides, many participants are able to participate in the consensus experiment without degraded performance. In the second problem, a smart manager system provides authentication of users and devices. The solution to the third problem related to confidentiality is to analyze the current RSA encryption method and supplement it with a proxy re-encryption method.