At its core, blockchain technology is a decentralized record keeping system that enables secure data storage through complex cryptographic methods. The thesis describes how blockchain technology works and what its key elements are, including blocks, accounts, transactions, consensus algorithms and smart contracts. It describes how blockchain can be used to build a digital identity management system. The SSI model and its importance in digital identity are also described. Users can provide verified information about themselves without revealing all their information, which provides a high level of security and privacy. Furthermore, the paper deals with the integration of Web2 and Web3 technologies, with a special focus on the advantages and disadvantages of such integration. Web2 refers to the currently dominant model of the Internet, which is based on centralized servers and where users are usually consumers of content. On the other hand, Web3 is a vision of the future Internet that uses blockchain technology to create decentralized applications. The final part of the paper is devoted to the practical application of the theory through the construction of an Express application that communicates with a smart contract on the Ethereum network. The application provides the basic functionalities of a digital identity management system, while demonstrating the concrete benefits and possibilities of applying blockchain technology in the real world. This thesis hopefully provides readers with a deeper understanding of the opportunities and challenges that blockchain technology offers in the context of digital identity.