CAN YOU HACK BTC*?

Every number below is two secret primes multiplied together. Find them and win a satoshi. This is how bitcoin keeps your money safe — sort of.

Mental math. · wins 1 sat

Fill in the blanks

×=?

▊ Pick a difficulty and get a target.

Crack a number and it’ll show up here.

The point: multiplying is easy; un-multiplying is brutally hard. Our nastiest number is 16 digits and a laptop still cracks it in seconds — but the keys guarding real bitcoin are so enormous that every computer on Earth couldn't crack one before the universe ends. That one-way gap is what keeps your coins yours.

* Small confession: factoring primes like this is RSA — the encryption behind most of the web — not bitcoin itself. Bitcoin uses elliptic-curve crypto, a different lock with the same one-way trick: easy forward, hopeless in reverse. We went with primes because a simple version of ECC seemed annoying to do.