Cryptocurrencies were initially promoted on their ability to operate in a fair and equitable manner free from financial institutions and governments. This paper evaluates sustainability issues facing cryptocurrencies in their functions as a form of private money. Specifically, we focus on their claims around inequality and poverty reduction using the United Nations Sustainability Development Goals framework. Our findings suggest that although the technologists believed they produced suitable alternatives to traditional money, there are a number of issues in regards to the sustainability of this form of finance. The major areas of the shortfall are around an energy usage perspective, the reward system for transactors to those with access to greater computer power (inequality) and issues over loss sharing when exchanges or user nodes are hacked and digital wallets are lost.