(en) Judmayer, Aljosha, Stifter, Nicholas(2017).Blocks and Chains: Introduction to Bitcoin, Cryptocurrencies, and Their Consensus Mechanisms (Synthesis Lectures on Information Security, Privacy, and Tru). Morgan & Claypool Publishers,'Before bitcoin',p. 17.ISBN 9781627057165.
(en) Blanchette, Jean-François(2012).Burdens of Proof: Cryptographic Culture and Evidence Law in the Age of Electronic Documents. MIT Press,'On the brink of revolution',p. 50.ISBN 978-0262017510.