I checked this out for New Zealand a while back
The IRD's position is that crypto currency is a form of income and is therefore liable for tax, just like any other income.

Then it gets fuzzy.

If it is taxed at source, i.e. you have already paid income tax on it, you don't have to pay tax again.
I don't think you have to pay tax in NZ for money earned overseas and not brought into the country.

So if I work in Fiji for six months, i don't pay tax in NZ on the money I earned in Fiji. It is assumed that I paid tax on it in Fiji and it is their government's responsibility to manage tax collection in their country.

But with crypto, it is not geo-based, so the whole scenario does not apply.

So if I earned bitcoin online and spent it online, with none of the money coming into the country the IRD has not jurisdiction to tax it. Maybe.

Because this is so new they don't really know if they should tax it or not. Their default position is, 'it's safer to pay the tax'.

Sooner or later this will be tested in court and then there will maybe be a ruling that they can apply.

But I think it is naive to expect governments to not try and tax crypto currencies.

For now it is just a matter of deciding which risk you are more willing to take - losing some money to the taxman, or losing all of it in court.

One way or another, they will have their pound of flesh.