In the upcoming years, most of the devices will be connected wirelessly, which also increases the risk of attacks like a DDoS (distributed denial of service) attack. Satoshi Nakamoto in 2008 described the bitcoin design. As the “Internet of Things” technology is emerging day by day, devices under this technology are also increasing in large numbers. Technology has increased rapidly from bluetooth low energy (BLE), radio frequency identification (RFID), to sensor technology, mobile devices, actuators, and global positioning system (GPS) devices. Internet of things (IoT) can play a huge role in making a city or home “smart” (Biswas and Muthukkumarasamy, 2016). The future of connected devices lay in the hands of IoT technology. But, with the increase in the “things” under IoT, concerns on securing these things also increased (Lee and Kim, 2017). Traditional security methods are highly expensive as well as centralized. On the other hand, a new emerging technology, popularly known as the blockchain, is totally decentralized. The blockchain is the technology behind the security of the first crypto currency, i.e., bitcoin. In addition to its decentralized nature, the blockchain is transparent, persistent, and secure. The blockchain can be considered as the future of not only IoT security but also in other fields, such as cryptography of multimedia networks which contains text, audio files, images or videos. As the IoT is growing up, sensors and devices are becoming more and more vulnerable to attacks and threats. In IoT, participants have to rely greatly on the administrator or the central authority of the network. Administrator is all powerful; he/she can delete or modify the data without any restrictions. Transactions made are not totally secure; data can 747be easily manipulated by any third party. When it comes to money, people trust a third party to complete a transaction successfully without any hindrance.