Tweetchain: An Alternative to Blockchain for Crowd-Based Applications Francesco Buccafurri (B ) , Gianluca Lax, Serena Nicolazzo, and Antonino Nocera DIIES, University Mediterranea of Reggio Calabria, Via Graziella, Localit`a Feo di Vito, 89122 Reggio Calabria, Italy {bucca,lax,s.nicolazzo,a.nocera}@unirc.it Abstract. The assurance of information in the crowdsourcing domain cannot be committed to a single party, but should be distributed over the crowd. Blockchain is an infrastructure allowing this, because trans- actions are broadcast to the entire community and verified by miners.A node (or a coalition of nodes) with high computational power can play the role of miner to verify and approve transactions by computing the proof of work. Miners follows a highest-fee-first-served policy, so that a provider of a Blockchain-based application has to pay a non-negligible fee per transaction, to increase the likelihood that the application pro- ceeds. This makes Blockchain not suitable for small-value transactions often occurring in the crowdsourcing paradigm. To overcome this draw- back, in this paper we propose an alternative to Blockchain, leveraging an online social network (we choose Twitter to provide a proof of con- cept). Our protocol works by building a meshed chain of public posts to ensure transaction security instead of proof of work, and no trustworthi- ness assumption is required for the social network provider. Keywords: Crowdsourcing · Blockchain · Twitter · Public ledger 1 Introduction Coordination, record keeping, and irrevocability of transactions are features that make the Blockchain technology exploitable not just for cryptocurrencies. Indeed, a variety of applications can be built on top of this technology, making Blockchain a registry and inventory system for the recording, tracking, monitor- ing, and transacting of all assets [8]. Blockchain is considered a robust platform: even though a number of possible attacks are known [1, 6, 7, 9, 10], they are mostly not relevant in practice. Blockchain is recently attracting the interest of both companies and researchers due to its power and the possibility to implement innovative solutions in those cases in which many users are spread over large spaces and may belong to different organizations. Despite this, there are a lot of situations in which the use of Blockchain appears not suitable. Indeed, in Blockchain, the consensus on c  Springer International Publishing AG 2017 J. Cabot et al. (Eds.): ICWE 2017, LNCS 10360, pp. 386–393, 2017. DOI: 10.1007/978-3-319-60131-1 24