Along with the central banks of many other countries, the Reserve Bank of India is also planning to introduce a blockchain-based digital currency. This move has been pending for long, as central banks have watched, with some measure of alarm, the astounding growth in cryptocurrencies and their spread in various kinds of transactions. Open, "permission-less" cryptocurrencies, like Bitcoin, are generated, held, and transacted upon by people all over the world. No central bank has any control over it, cannot determine its exchange value, cannot "demonetise" it, cannot check its inflation or deflation, and cannot control its issuance. These are things central banks can do with "fiat" currencies, like the Indian rupee: they issue, own, distribute, fix the exchange rate, and determine the legitimacy of all rupee notes and coins.