The technology of cryptocurrencies represents a breakthrough technology in the development of digitization. Cryptocurrencies are a type of digital currency based on cryptographic principles for confirming transactions. Various cryptocurrencies use various types of proofs. The aim of this review article is to analyse the proof of work, that is the oldest type of algorithm for the creation of blocks. The article should contribute to the cryptocurrency theory technology, and also should provide benefits to the evolution of information technology and technological innovations.