On cryptographic signatures. Lets say instead of passport you have to make a transaction to the government that contains your biometric picture. Any time in the future you can prove *WITHOUT A DOUBT you are the person who made the transaction as long as you still hold the keys. Keys can be stolen same as ID can be, but can't be forged. Identity cannot be stolen for online uses in traditional ways because having the information is not enough, you have to have the KEYS !