We provide the first systematic exposition of the second generation of cryptocurrencies, including Bitcoin and the many alternatives that have been implemented as alternate protocols or ``altcoins.'' Drawing from a scattered body of knowledge, we put forward three key components of Bitcoin's design that can be decoupled, enabling a more insightful analysis of Bitcoin's properties and its proposed modifications and extensions. We contextualize the literature into five central properties capturing blockchain stability. We map the design space for numerous proposed modification, providing comparative analyses for alternative consensus mechanisms, currency allocation mechanisms, computational puzzles, and key management tools. We focus on anonymity issues in Bitcoin and provide an evaluation framework for analyzing a variety of proposals for enhancing unlinkability. Finally we provide new insights on a what we term disintermediation protocols, which absolve the need for trusted intermediaries in an interesting set of applications. We identify three general disintermediation strategies and provide a detailed comparative cost analysis.
Category / Keywords: applications / survey Original Publication (with minor differences): IEEE Security and Privacy Date: received 19 Mar 2015, last revised 23 Mar 2015 Contact author: jbonneau at cs stanford edu Available format(s): PDF | BibTeX Citation Note: eprint report number updated Version: 20150323:173252 (All versions of this report) Short URL: ia.cr/2015/261 Discussion forum: Show discussion | Start new discussion