Hashcash

Hashcash is like a puzzle that you solve on the computer. You know how you put together a puzzle with all the pieces that fit perfectly together? Hashcash is like that, but instead of making a picture, you're trying to make a code that is unique and hard to guess.

Hashcash is used to prevent bad people from doing bad things on the internet. When you want to do something important like send an email or make a financial transaction, you have to prove that you're a good person and not a bad person. Hashcash helps you do that by making you solve a puzzle that lets everyone know you're a good person.

Hashcash makes the puzzle hard to solve by making you do something called "hashing." Hashing is like putting a secret message through a blender. Once it's been blended, it's really hard to put it back together, and that's what makes it secure. The puzzle you have to solve is trying to un-blend the message, and if you can do that, you get to prove you're a good person.

Hashcash is used a lot in things like email and cryptocurrency, where it's really important to make sure that the person sending the message or making the transaction is who they say they are. It's kind of like having a secret handshake that nobody else knows, and that's what makes hashcash so special.