Making a Custom Hashcat Module to Solve a Decade-Old Puzzle Challenge

Learn how to develop a custom Hashcat module through the lens of solving the decade-old "One Bitcoin Book" puzzle challenge in this DEF CON 33 conference talk. Explore the 2014 cryptographic puzzle created by Spencer Lucas, which consisted of 20 clues that, when solved, would unlock a bitcoin wallet containing one bitcoin that remained unclaimed for over 10 years despite its six-figure value. Discover how the prize was finally claimed in December 2024 through a combination of human problem-solving and custom cryptographic tools. Examine the brainwallet process used to unlock the prize and understand how the puzzle answers were converted into the winning solution. Master the development process for creating specialized Hashcat modules designed to crack brainwallet passphrases using cost-effective cloud-based GPU computing power. Analyze the technical challenges encountered during the module development process and learn practical troubleshooting approaches for overcoming complex cryptographic obstacles. Gain insights into combinatorial testing methods for handling uncertain or partially-known clues in cryptographic puzzles.