Yes currency trading is permitted on CubePlus subject to certain regulations introduced by the Reserve Bank of India. RBI has mandated traders to compulsorily have an underlying contracted exposure to foreign currency if they want to trade in the currency derivatives segment. 

If a trader has an exposure greater than $100 million (i.e. notional contract value), they will be required to appoint a custodian participant or an authorised dealer. However, for traders with a smaller exposure, a declaration that you are trading currencies to hedge your contracted exposure will suffice.