«Adam has extensive practical experience building teams and shipping products as shown by his track record at organizations large and small, such as Microsoft, PI, EMC, and VMware, this is on top of having an extraordinarily deep technical background in all aspects of cryptography and being the inventor of Hashcash, one of the core concepts used in Bitcoin.» (bitcoinist.com)
Bitcoin use Hashcash proof of work system, for block generation. (coinscage.com)
To prolong the blockchain, bitcoin uses Hashcash puzzles developed by Adam Back in the 1990s. (en.wikipedia.org)