Illegal in any country. Mixing coins is illegal because it is technically laundering. If you earn money illegally, like from Silk Road, or in real world and convert it to bitcoin, then mix bitcoin and convert to dollars, that is technically money laundering. I am mainly interested in discussion for how to keep money secret and hidden. Such involves mixing, anonymity, and not reporting foreign income, foreign wealth, or capital gains. Ideas for how to hide bitcoin and still be able to spend it without being caught would be nice, but I do not know if this would be allowed.