the government has no right to tax that is not provided by their laws. Cryptocurrency has an indefinite status in the state. It is therefore not subject to tax
Which state do you refer to?
For example, in the US Bitcoin has been classified as "a convertible decentralized virtual currency" in 2013, which is considered as property and should be taxed as such. In the EU it is also classified as a decentralized virtual currency, though it is exempt from taxes because of its similarity with cash, i.e. it is considered as a means of payment (in other words, money). In China, it seems to be thought of as a so called Civil Rights Object (something like a property right), and it is legal for private use and ownership