The math problem unsolve which could be worth a billion dollars

The algorithm that no one on earth has been able to reverse. Yet it's really easy to compute one-way. You could make billions of dollars if you solved this mathematics problem, which is computed quintillions of times per second in the race for mining Bitcoin. SHA256 has some amazing properties, is useful for digital signatures, cryptography, authentication, and is a central part of the Bitcoin protocol.

(**** UPDATE 2021: After two years, I've finally posted a follow-up video, an introduction to Bitcoin. You can find it here: https://youtu.be/LzhJjSRad5A )

Bitcoin and other "crypto-currencies" rely on one-way hash functions like the SHA-256 algorithm to secure the blockchain where all the transactions are kept.

In this video, I explain some of the big-picture ideas behind this one function. Other cryptocurrencies use similar ideas.