Bitcoin. Hashcash is the mining function used in bitcoin. There are minor differences between the variant of the hashcash mining function used for X- Hashcash. Hashcash. A core building block of the Bitcoin protocol is the Hashcash concept. Bitcoin uses Hashcash to provide security from malicious alterations of the. A look at how the technology underlying Hashcash — proof of work — would shape research into digital money for more than a decade to.