The contribution provides a short treatise on search for legitimacy of the definition  authority through the theory of social contract applied on the environment   of the blockchain technology. Pursuant to the introductory summary of the historical  evolution of this crucial theoretical concept is the attention focused on limits,  which are for it created in the cyberspace environment. Next is mentioned  the role of definition authorities and their significance in this context. Focus is  afterwards shifted to the blockchain technology, as a potential innovative legitimacy  model, which amply combines the requirement of implicit support by the  majority with the need for exercise of authoritative power through a mechanism  with a real impact on the given environment. Based on an analysis of the system  of creating trust, changing definition norms and organisation of the share on  authoritative exercise of power within this platform, an opinion is formulated  that this new technology may on one hand transfer the issue of legitimacy to  a new level; however it does not solve it in its own nature.