Contents I. Introduction
The Internet of Things is nowadays in a continuous expansion [1]. Smart cities, intelligent houses and other applications require communication between a lot of nodes which usually consists of low or medium computational power and small memory amount microcontrollers. Generally, the IoT systems use a server-client communication model in which the devices are identified, authenticated and connected through servers with high computation and storage resources. The devices have a unique identity and they are connected through Internet. Nowadays this communication paradigm will not longer be used due the huge growing of the number of IoT devices. The centralized solutions became expensive – they use many servers and networking equipment to ensure the communication between billions of devices and they need maintenance. Decentralized methods represent solutions that answer to the high costs issue in huge IoT systems. The computation power and storage requirements will be shared among the devices in the network. However, the peer to peer communication arises some important issues to solve: privacy, security, data validation and consensus.
