‘So, Professor Shin, tell us what you really think about cryptocurrencies.’ I’m guessing that’s the brief the Bank for International Settlements (the Basel-based central bank of central banks) gave economist Hyun-Song Shin to write a chapter for its annual report, published this week. His response delivers a serious kicking to the whole befuddled concept of ‘permissionless’ online currencies that ‘promise to replace trust in long-standing institutions such as commercial and central banks’.