This makes a lot of sense to me. Why don't we use this system? The main risk I see is that an individual might lose both the "computer card" (today it'd be your mobile phone) and the backup version of the look up table of pseudonyms and service providers / partners. Another question: if a bank needs to report interest or capital gains to the taxing authorities, would they report using a unique pseudonymous identity? If that's so, then how would the taxing authority know from whom to collect the tax?