The goal of the thesis is creating the basic environment for understanding Blockchain technology, especially the Ethereum network. The use of methods that guarantee the security of personal data is essential when managing data on distributed ledger. Also, this thesis aims to familiarize the reader with the innovative technology of Blockchain and the benefits offered by its adoption in the field of security. Initially will be refer to the definition and basic concepts of technology as well as its operation. A special analysis will be made in the concept of smart contracts and the role they take part in the operation of technology and in the implementation of applications. The Ethereum as an open-source platform based on Blockchain technology will be used to design and implement of the solution. It will take advantage of the possibility offered by the platform for the writing and operation of smart contracts as the user desires. The main object of study in this project is the security of Blockchain technology and how it works. The benefits of a Blockchain-based framework create a reliable and transparent data storage and mangling environment. Security will be assessed based on the personal data of users stored within the network. In particular, it will be examined in the light of medical data of patients who are sensitive personal data and require a high level of security. It will also present the logic of data access controls through the UMA mechanism that gives the user the choice of who has access to the data they hold. Based on the above criteria, a Remix environment it is created with smart contracts of the basic operation of solidity program language.