Muhammad Abu Bakar, a certified Mufti (Muslim legal expert) explains in his article for Blossom why cryptocurrency could be considered Halal.
1) Cryptocurrencies are not controlled by a centralized system what makes them more secure than other current money systems
2) Cryptocurrencies are widely accepted; hence, it is money
However, Abu Bakar marks that while cryptocurrencies are halal in most cases they are not halal at all. For instance, they are not halal is jurisdictions they banned. He also stated that it is not advisable to use cryptocurrencies for investments purposes.