In recent years, networked computers areextensively used in every aspect of our daily lives. Besides, the anonymousstructure of the Internet results in an increase in the number of attacks notonly for individual users but also for local area networks. Current attacks aremore sophisticated, and they are developed by experienced intruders with theuse of automated malware production methods. These organized intrusions can goover the defense lines of the systems due to the weakness of thedetection/prevention mechanisms or carelessness of individual users. Aftersneaking into the system, these attacks can work until they are detected, andthey can access many critical resources of the company. Earlier detection ofthese attacks is very trivial issue for the security admins. This can beaccomplished by acquiring the signature (critical information) of the newestattacks as early as possible. One suggested solution is the use of a Threat Information Sharing system, whichis set up between security firms and authorities. This approach enables thedistribution of the marks of the recent (zero-day) attacks and the developmentof some proactive prevention mechanisms for them. The use of both peer to peerand centralized sharing mechanisms have some inherited deficiencies. Therefore,in this paper, a pure decentralized cyber security information sharing systemis proposed with the use of blockchain technology. A controlled decision-makingmechanism, authorization termination, and rule-sets maintenance are proposed tomake distributed decisions within the system. For making a decision, two smartcontracts should be used in the blockchain. One holds the positive votes whilethe other holds the negative ones. Members of the system are able to accesscyber threat data by using company-related queries. The system can facilitatethe integration of many data sources into cyber security management system.Additionally, it enables to collect in a single repository that can be accessedfor implementing real-time cyber security applications.