Adam Back, is a UK cryptographer who created the Hashcash mining algorithm used in the Bitcoin network. He is the CEO of Blockstream, the company which hires the majority of active Bitcoin Core (BTC) developers. He has worked on e-cash protocols since 1995. Some of the companies he has worked for include Credlib, Nokia and later Credentica (acquired by Microsoft).

Adam Black has also worked as an architect and cryptographer at Zero-Knowledge Systems working on its Freedom network, a prototype to Tor. He has also consulted for leading security companies, including oneID, Vmware and QWcap. He obtained a Computer Science PhD degree from University of Exeter in the Distributed Systems research field.

Back’s company, Blockstream, provides funding for the evolution of Bitcoin Core, the prominent bitcoin network client software. It also employs a large number of leading Bitcoin Core developers.

Black was one of the first two people to receive an email from Satoshi Nakamoto In 2016. The Financial Times referred to Back as a potential Nakamoto candidate, along with Nick Szabo and Hal Finney.

As a well-respected figure in the blockchain space, Black has an active presence on Twitter where he often engages in interesting technical conversations with his followers

How does Hashcash work?

HashCash was developed by Adam Black to fight email spam. By making each email cost a bit of computing time, which the email sender would have to prove by cryptographic means, mass email could be made costly and difficult to send. This makes it worthless to embark upon by spammers.

The hashcash algorithm is quite simple to understand and execute. Hashcash continually hashes the same data over and over, with little differences every time, until a hash is found with a predefined number of leading zero bits. After hashcash finishes mining and returns control to the prompt the screen displays three time fields. The user time field roughly displays the amount of CPU time used by hashcash. The time taken by CPU to process the hashcash increases with increase in the level of difficulty.