These mechanisms can take various forms, but all seek to offer sufficient certainty to system participants as to the correct status of the transaction ledger at any moment in time. One of the most well-known tools is the so-called proof-of-work or PoW, which requires complex and costly – primarily in energy consumption – computational calculations. It is precisely this latter aspect which is expected to deter irregular behaviour on the part of validators. However, the price of electricity, concerns about the environmental impact, the limited access to the specialised hardware required and scalability problems are some of the factors that are encouraging gradual migration to other types of solutions.8 Proof-of-stake or PoS is one such alternative. Its main characteristic is that validators are selected according to their direct economic stake in the network; in other words, depending on the amount of crypto-assets they own and must block to ensure that the operation is validated correctly. As they have a direct interest in preserving the value of the crypto-asset, in principle, this mechanism creates incentives to behave honestly. Moreover, as the possibility of their being assigned operations is generally connected with the volume of crypto-assets blocked, the network is less decentralised than under the other mechanisms. Although there are more options, where blockchain networks are set up as closed circuits (permissioned networks), a third mechanism, dubbed proof-of-authority or PoA, is generally prominent.

32  FATF (2021), “Updated Guidance for a Risk-Based Approach Virtual Assets and Virtual Asset Service Providers”. 33  https://ec.europa.eu/info/publications/210720-anti-money-laundering-countering-financing-terrorism_en. 10  In this respect, matters such as restricting said activities to supervised deposit institutions,34 constraining reference assets to higher quality ones and imposing transparency measures on the latter35 are emerging issues that could ultimately become global trends. At the national level, in Spain there are no specific regulations on crypto-assets. The Spanish National Securities Market Commission (CNMV) has issued a circular on advertising of crypto-assets intended for financial investment36. The circular aims to ensure that the advertising content is accurate, easily understandable and not misleading, and that it clearly includes mention of the associated risks, including the possible loss of the entire investment. As such, this regulation establishes the tools and procedures for effective supervision of crypto-asset advertising, but it does not regulate either crypto-assets, their issuance or crypto-asset-related services And, since October 2021, the Banco de España37 has held a special register of providers, although its scope is currently restricted to only a subset of players.38 Unlike other registers, this one has a limited purpose, catering only for anti-money laundering and counter terrorist financing needs. In other words, an entity’s inclusion in the register does not imply that it has been granted prudential authorisation, i.e. it does not guarantee that the agent is solvent or has the technical capabilities necessary to correctly pursue its activity. Nor does the register impose specific transparency requirements vis-à-vis the agent’s clients.