The legality of bitcoin depends on who you are, and what youre doing with it.
There are three main categories of bitcoin stakeholder. Someone may fall under more than one of these categories, and each category has its own legal considerations.
It really depends on which country we are domiciled, if in a country that rejects bitcoin it is clear that bitcoin is illegal because the state applies illegal status, but on the contrary if we are in a country that supports and legalizes bitcoin then the status of bitcoin becomes legal or official, but what is certain is bitcoin only a digital currency which certainly does not violate the law.