"It's maybe private in that the Vintner does not need to know who you are, but you can bet the control freak tyrants in the government will know that you bought that wine." -- actually no. Because the digital cash you "extracted" from the exchange was blindly signed, the exchange/central bank would NOT learn that you bought wine. Only that someone (anyone who previously withdrew a sufficient amount of digital cash) bought wine. Please do read up on cryptography, how to do this is known since 1989.