Explore a critical analysis of cryptocurrencies and blockchain technology in this 22-minute conference talk from USENIX Enigma 2019. Delve into the fundamental issues surrounding these technologies, including their incompatibility with modern finance, lack of practical use cases, and potential vulnerabilities. Examine the speaker's arguments on why cryptocurrencies may only be suitable for censorship-resistant transactions and how they might be susceptible to technical, legal, and social attacks. Learn about the concept of "smart contracts" and their potential pitfalls, as well as the speaker's perspective on how cryptocurrencies may be replicating historical economic failures. Gain insights into proposed actions for addressing the challenges posed by cryptocurrencies, including legal enforcement and technical countermeasures.