The evolution of privacy in the blockchain: A historical survey

Abstract

In order to store information in a decentralized context and without the presence of a guarantor authority, it is necessary to replicate the information on multiple nodes. This is the underlying idea of the blockchain, that is generating increasing interest nowadays as one of the most-promising disruptive technologies. However, the ledger is accessible to all participants and if adequate precautions are not taken, this may lead to serious privacy issues. Present paper retraces the history of blockchain with particular attention to the evolution of privacy and anonymity concerns, starting from bitcoin. Furthermore, this work presents the most popular solutions to ensure privacy in the blockchain, as well as the main cryptocurrencies that have been proposed after bitcoin to overcome this problem. A critical survey is presented classifying the approaches in mixing protocols and knowledge limitation protocols. Open challenges and future directions of research in this field are proposed.