There's always been an untraceable currency sold and traded globally. Gold. You can't trace it back to the origin, as long as it's been melted down.
The only thing is, you can't easily transport it. And lets be honest, how many people are willing to accept gold?
This is scary stuff for governments all over the world, not because you can buy drugs or use the currency for illicit reasons, it's because -- taxes and bypassing traditional financial institutions. (Just think paypal)
If you can move money around the world securely and anonymously, you can hide your money from the tax man. At least in theory...
I'm not sure you can do that with gold because there's only one stable/naturally-occurring isotope, and the most stable other isotope has a short half-life of six months. Labeled gold's radioactivity may be a give-away.
You don't need to add the impurites, they're already there. Metals have fairly distinct patterns of impurities depending on where they were mined from and it's basically impossible to entirely remove them. If you expose a sample of metal to a large flux of neutrons (usually in a reactor) then the nuclei of the various elements in the metal will absorb neutrons and then decay. The products of these decays can then be analyzed to work out the composition of the metal even if an impurity is very small. This type of analysis has been common for a very long time now. An example of a current use is determining the country of origin for controlled metals like plutonium and uranium.
There are ways to get around this kind of approach (by adding impurities, not removing them) but I felt like mentioning it because it makes a lot more sense in this context than isotope fingerprinting.
The problem is not how many people are willing to accept gold it is there are not enough people willing to pay with it.
Very large financial transactions on multi-currency, multi-nation, trading markets use Gold and Oil Futures as currency.
There are storage facilities around the globe that will actually move physical gold from one private 'vault' to another and confirm the transactions. The end user has an interface similar to online banking and doesn't have to leave their desk.
The only thing is, you can't easily transport it. And lets be honest, how many people are willing to accept gold?
This is scary stuff for governments all over the world, not because you can buy drugs or use the currency for illicit reasons, it's because -- taxes and bypassing traditional financial institutions. (Just think paypal)
If you can move money around the world securely and anonymously, you can hide your money from the tax man. At least in theory...