On Some Approaches to the Solution of the "Useful Proof-of-Work for Blockchains" Task

The blockchain technology is based on the proof-of-work principles. The essence of this principle is that some event (for example the bill-to-bill money transaction) becomes significant after the confirmation by certain computer work. So, a demand arose for such computational problems to work on, and we will spend for it about the whole blockchain system computing capacity. Now the main class of such problems is a hash-puzzle - the problem to find a bit string with a hash that satisfies some conditions. The major hash-puzzle weakness is the lack of the useful application outside of the blockchain technology. In this work, we offer some approaches to the Useful Proof-of-work for blockchains task, namely, we consider some practical variants of the NP-complete problems (tasks) that could be solved with the help of SAT-solvers as the proof-of-work computational problems. The use of the FPT-problems requires special study. The approach offered allows to provide the following characteristics of the proof-of-work computational problems: usefulness, problems complexity management (through the dimension change, choosing problems of certain type, the indication of necessary solution precision), mass character. Herewith we admit that not every solved task can be useful but we consider the opportunity to solve some practical tasks with the help of the blockchain technology. Among other things it is also possible to compare the virtual crypto-currency value (through the energy costs spent) and the effective result of the practical problems solution. The most complicated points of the described approach are the realization of the events-tasks (providing the computer work for these events) relations and the realization of the tasks complexity analysis system. This issue should be viewed as a research program because of many technical details that must be worked out further.