Ero sicuro che qualcuno avrebbe pensato a combinare digital labor e bitcoin mining (bastava cercare "human proof of work"). Chiaramente saranno solo attività "fun, educational and beneficial to society". L'immagine di un capannone pieno di diseredati che cliccano captcha evidentemente non sfiora gli autori... <https://eprint.iacr.org/2016/145.pdf> [...] At its core, Bitcoin’s distributed consensus protocol is based on moderately hard Proofs of Work (PoW) [24]. In Bitcoin the Hashcash [3] PoW puzzles are used to extend the blockchain, a cryptographic data-structure in which the public ledger is recorded. A PoW puzzle should be moderately hard for a computer to solve, but the PoW solution should be easy for a computer to verify. Cryptocurrencies like Bitcoin require that this hardness parameter of PoW puzzles be tunable. An adversary would need to control 51% of the computational power in the Bitcoin network to be able to alter the blockchain and prevent users from reaching the correct consensus 1 . While Bitcoin cleverly avoids the Sybil attack by using PoW puzzles, there are still many undesirable features of this distributed consensus protocol. For example, construcing the proofs of work is energy intensive making the mining process in this distributed consensus protocol environmentally unfriendly. Furthermore, the mining process is dominated by a smaller number of professional miners with customized hardware making it unprofitable for others to join — this raises the natural concern that a few professional miners might collude to alter the public ledger [47]. Indeed, the mining pool GHash.io 2 recently exceeded 50% of the computational power in Bitcoin. While other techniques like Proofs of Space [48, 26] or Proofs of Stake [8] have been proposed to build the blockchain in a distributed consensus protocol each of these techniques has its own drawbacks. It is clearly desirable to find new techniques for reaching a stable distributed consensus. In this paper we ask the following question: Is it possible to design proof of human-work puzzles that are suitable for a decentralized cryptocurrency? We believe that a cryptocurrency based on Proof of Human-work might offer many advantages over other approaches. First, the mining process would be eco-friendly. Second, instead of wasting ‘human cycles,’ it might be possible to base the proofs of human work on activities that are fun [35], educational [34] or even beneficial to society [57, 36]. Third, proofs of human work are fair by nature in the sense that two individuals will generally perform a comparable amount of work to produce a proof of human work. Thus, professional or rich miners would not have an significant advantage over regular users. [...]