New Delhi, Aug. 28 -- India's Unified Payments Interface (UPI) was launched in 2016. Ten years on, UPI boasts of 240 billion annual bank-to-bank transfers, with their total value raring to rival nominal GDP.

Stupendous as its success has been, the world of digital money remains obsessed with crypto. Bitcoin, the archetypal example, was a rebellion against folly-prone human control of money supply. Its launch pitch, drafted under a pseudonym, made an elegant case for an open ledger run by an algorithm.

In a nutshell, its confidence winner was this: just as a coin loaded in favour of one side-let's call it integrity-that's tossed multiple times will move the outcome tally towards the coin's bias, so will honest actors drive out the bad on...