In the present thesis, firstly we study the centralized protocol of the blank signature [23], a new type of signature that was published by Christian Hanser and Daniel Slamanig , in 2013,as well as the security of this scheme. The existence of centralization in the above protocol, as we will see, is a crucial part because if we ignore it, one of the participants can find a trapdoor to the protocol. Consequently we refer to the decentralized protocol of Bitcoin [3] that was published by Satoshi Nakamoto ,in 2008 ,as well as the security with which it provide us [1],[2] , and we also refer to some smart contracts [12] that has been built on top of this ,which use its decentralized character. Lastly, we refer to the new decentralized system, the Ethereum[21],[22], that was introduced by Vitalik Buterin, Gavin Wood ,in 2013- 2014 (during this thesis ,its development has been growing),which advantages it wants to achieve in comparison with the Bitcoin as well as the formal way of its function .