Preface -- Fundamentals of Blockchains -- Proof-of-work: A Consensus Mechanism to Achieve Consistency -- Misunderstandings and Expectations of the Blockchain created by Bitcoin -- Misunderstandings and Expectations of the Blockchain created by Bitcoin -- Challenges blockchain technology faces -- Are Blockchains Trustless? -- The Bitcoin "Consensus” Problems -- The Myth of "Blockchain is Scalable" and Real Challenges -- Unexpected Pitfalls of Bitcoin -- The Biggest Problem of Blockchains: Key Management -- The Cryptographic Technology of Bitcoin will Eventually be Broken -- How We Can Secure Blockchain-based Systems -- The current state of the global movement.