You have never walked anonymously. You may have believed otherwise, pulling a hood over your head or choosing the busy side of the street, but the truth has been catching up for years. The way you shift your weight from one foot to the other, the cadence of your stride, the particular rhythm of your fingers on a keyboard, even the micro-fluctuations in your voice when you order a coffee: all of these patterns are, increasingly, as identifiable as your fingerprint. And unlike your fingerprint, you leave them everywhere, involuntarily, continuously, without ever pressing your thumb to glass. Artificial intelligence systems can now identify individuals through subtle behavioural patterns and voice characteristics with startling accuracy. Gait recognition software deployed on the streets of Beijing and Shanghai can pick you out of a crowd from 50 metres away, even with your back turned and your face completely covered.…