Before Bitcoin was released, there were a number of digital cash technologies starting with ecash by mathematician David Chum in 1987, and Stephen Brandes in 1997 Adam Buck developed hashcash, a proof-of-work against spam.
. From 1998-2005, WeDee launched the idea of decentralized cryptography. Nick Zuber developed the "bit gold" project, which is a digital currency based on decentralization, such as using many elements that we find in Bitcoin, and this system has been subjected to a strong attack.