DEF CON 33 - Making a custom Hashcat module to solve a decade-old puzzle challenge - Joseph Gabay

In 2014, someone by the name of Spencer Lucas released the “One Bitcoin Book“, a set of 20 clues that when solved, unlocked a bitcoin wallet containing one bitcoin (then valued at ~$400). Over 10 years and a six-figure price tag later, it remained unclaimed. In December 2024, the prize was finally claimed through a combination of human-solved solutions and a custom module for Hashcat designed to test various combinatorial possibilities for the unknown or uncertain clues. This talk will cover the puzzle itself, how the answers unlocked the prize (through the brainwallet process), and the development of a custom Hashcat module to crack brainwallet passphrases using cheap, cloud-based GPU power. It will also discuss the challenges encountered along the way and the troubleshooting approaches used to overcome them.