In a couple of weeks, the shadowy billionaire Satoshi Nakamoto — whoever he is, wherever he is — will celebrate his official birthday. The paparazzi, yakuza and Interpol will never know who he parties with on April 5. The famed anonymity that shields him from the world is also at the core of his creation, bitcoin, and the technology it rests on. Anyone can track a crypto coin moving from one wallet to another, like following a courier shipment
