Once upon a time, there were four good friends. Every day they would borrow some of each other’s lunch money if one of them didn’t have enough. One day, Lynesse realized that they couldn’t keep track of all the money they were borrowing from each other properly so they could give it back. Because of that, they got mad at each other and would yell and fight over who owed who what money. It was then, Lynesse knew she had to save their friendships. Until finally, she found the secret magic that would change things forever.


    The lunchroom debate

Lynesse sat squinting at her notebook, pencil scribbling. She had to finish these math problems for Mrs. Sobe before lunch was over. Her lunch was still in the bag, and that didn’t go unnoticed by Danny. He, Byron, and Kanilla made it to the table and plopped down with their lunches. Danny asked why Lynesse wasn’t eating, and she answered without ever looking up that she was doing her math work and didn’t have time for food. Byron took a bite of his sandwich. And while still chewing, asked if Kanilla had the money she owed him from the other day. Kanilla looked puzzled and replied that she didn’t owe him anything. Danny thought they were gonna get in another argument.

Lynesse finished her final problem and closed her notebook. She looked at her friends and told them it was Friday, and you know everybody who owes money to someone puts it in the middle of the table first. Then, everybody who is supposed to get paid back takes what they’re owed out of the pile. We do it like that every week, but you guys always wanna yell first. Byron and Kanilla now both quite seemed mad at Lynesse.

Kanilla said that she sometimes forgets what she borrowed or owed because she isn’t good with numbers. It was then that Danny finished gulping his soda and reminded the group about the time they tried to let Amber into the lunch group, and she lied about Danny owing her money. But, since he couldn’t remember well, he put it in the pool, and she took it. It was only later we found out she had lied. Lynesse scrunched her mouth to the side in thought and told the gang she’d figure something out and bring it Monday. In the meantime, we’ll go ahead and do it like normal. And so they did and finished lunch and the rest of the school day.


    Lynesse makes a ledger

The lunch bell rang, and everyone shuffled off to the cafeteria. The gang met up at their usual spot. And Lynesse wore a face of smug satisfaction. With a grin pulled out her phone and commanded the others to do it as well. She instructed them to visit a calendar app or ledger just for them. It only had Monday through Friday, and each day could hold a list of who owed who money. Lynesse explained that all you have to do is click the first box and pick your name, then the second box and click the other person’s name. And finally, to type in the money you owed.

Everyone seemed to like the ledger. No one had to remember anything except to enter the information. Finally, Lynesse fixed all their problems. That is until the next day.

Danny didn’t show up for lunch, and the gang wondered what was going on? They tried to text him, but no response. Maybe he was in trouble? They weren’t sure but were surely worried. Finally, Bryon caught up with Danny later in the school day and asked him what was wrong? Why wasn’t he at lunch? Danny’s head hung low, and he wore a frown. He told Bryon that some kid must have stolen his phone because he left it sitting down for just a minute, and now it was gone.

It was then that Danny’s eyes widened. He looked right at Byron and told him that now anyone could write in their app, and it’ll look like it was me. But Byron reminded him of something Lynesse had said earlier. Each one of the group has a secret key. And every time Danny writes on the ledger, it’s linked to his secret key through a public key attached to the message. And every message public key is just a little bit different from the others. So, if someone tries to copy the message, it’ll show up in red on the ledger because it’s not really a new message, just a copy. Byron saw that Danny didn’t quite get it, so he tried another way.

Byron began, you know how when you sign your name, it’s the same every time? Well, the way this signature works is that it’s a little different every time and the way everybody knows it’s really from you is when the public key talks to the secret key that only you know. So, if somebody makes a copy, their signature’s public key can’t talk to your secret key because they don’t have it. So, it shows up as a bad message. The light flipped on in Danny’s eyes. Bryon placed his hand on Danny’s shoulder and said, let’s see if your phone is in the lost and found, and sure enough, it was.


    The ledger gets destroyed

It’s now mid-week at school, and things are going pretty well for our gang. Danny got his phone back, and no one tried to put false information on the ledger. So, everybody knows what everybody owes. But then, at lunch, when the gang tried to get on the ledger, nothing happened. They couldn’t get it to work no matter what they tried. Eyes began to widen, and frustration built. They all started looking at each other like, what are we gonna do? And still, there was a bigger problem. Danny needed money today to buy a drink, but now no one knew how much money they owed. And the yelling and fighting got so bad the attendant came over to break it up. Lunch ended, and no one was speaking to each other.

Later that night, at home, Lynesse would speak with her dad. You see, honey, I stored the ledger in a central place. Like when mommy and daddy store their money at the bank, we can spend and put money in when we want. That’s called a centralized place. Your ledger was like that. I made a website, and you and your friends could log into it and record your money. But, now that place is gone, and there was no way to get it back. Something happened that wiped out the whole thing. I’m sorry. Maybe I can think of another way. Lynesse, glum, slogged to her room and crashed on her bed. She thought she had fixed the problem, but now things were worse than ever.

The next morning, Lynesse made her way to the kitchen, getting ready for school, when she saw her dad at the table already. He was up early and with a smile on his face. Come here, honey, he said. Look. Her eyes rounded along with her mouth in shock. The ledger! Dad had found the ledger. And not only that, the ledger was no longer centralized. He told me that as soon as I saw my friends again, my phone would send a copy of the ledger. And that every time after that, we added a line to the ledger, it would send itself to everyone over the internet. That way, everybody had a copy, and there would be less risk of losing it.


    Will the real ledger please stand up?

Lynesse came to lunch that Thursday, bright and beaming. Her friends were there but sitting at different tables. She approached each one of them with the new ledger, and after a bit of talking, they were all at the old table again. There was laughter and talking and eating, of course. Everyone was so happy. Lynesse had done it again. That was until Kanilla said these next words. So, what happens if our phones can’t all talk to each other and Friday rolls around and we all have ledgers with different stuff on them? Maybe one of us loses service to our phone. Or, one of our phones gets messed up or stolen like Danny’s, except forever? Then, he gets a new phone and doesn’t have the ledger when we pool our money on Friday. Or, what if somebody copies an old ledger and overwrites theirs? How do you agree on which ledger is the real one?

This new ledger problem was terrible. Kanilla felt bad for making everyone sad, but she couldn’t help but think of the possibility. Everyone at the table was quiet. It was then that Mrs. Sobe came over to the kid’s table. She asked why they all looked so glum? As they explained the situation to her, Mrs. Sobe stood thinking about their words. You know kids, she said. You have this ledger that has lines in it that can’t be repeated or forged. So, what if you did that with each week of your ledger? For example, each week’s worth of ledger recordings, we can call a block. And when your group completes the block, everybody’s phone must agree that it’s the real block.

The way you can do it is to have a special code with each block, like a puzzle. All the phones will work to try and solve the puzzle, and the first phone to solve the puzzle gets to say that ledger is true. When the phones talk to each other and see the first phone to solve the puzzle, they will agree that it’s the right ledger and update themselves to that one. We’ll call it proof of work. That way, someone can’t just forge a ledger or make up lines because you’ll have your unique signatures for each line and each block. And the ledger or block isn’t real until someone solves the puzzle.

The kids were delighted. But Byron had a question. Mrs. Sobe? What if someone gets my phone and somehow changes the ledger anyway and then solves the puzzle? Mrs. Sobe thought a moment. Well, then what your phones can do is all solve the puzzles on their own, compare them, and agree that it’s the right block. Also, the phones will wait for a few blocks before reaching an agreement. Finally, the blocks link together, one after the other, with the information from the previous block in them. They’ll form a chain of blocks or blockchain. Afterward, all your phones will look and see which blockchain is the longest. The longest chain is the real information.

Then if someone takes your phone, Byron, they would have to solve more blocks than the other three phones combined. And that just isn’t likely to happen. Now, if more friends join your group and decide to be mean and make a blockchain that’s wrong but longer than yours, that could be a problem. So, you’ll have to be careful who you let in your group. When bad people can make more blocks than everybody else, we can call that a 51% attack because it would take just a little bit more than half of your computer power to make a fake blockchain.

What do you all think? The kids seemed content and decided to get Lynesse to talk with her dad.


    New Kids on the Blockchain

Friday came, and the kids were sending and receiving blockchain data from each other. Each phone worked to make sure each block was right and created several blocks before deciding which chain was real in case of any problems. The kids did move the day they settled their money with each other to the end of the month, but it worked out much better, and they didn’t have to think about anything but typing in when they paid money to one another.

Their friendship had been on rough waters, but blockchain saved it through its power. Lynesse thought that maybe if the whole world were on a blockchain, they could keep many things in better order than they do now. Maybe people could use the blockchain for voting or general recording keeping for a whole bunch of things. Maybe one day, she would create new ways for blockchains to help everybody in the world and make it a place where people could sit down for lunch and laugh and talk instead of yelling and fighting all the time.


    Finale

And they lived happily ever after. Or at least until they get to middle school. Can blockchain help with puberty? Maybe someday. Until then, Lynesse and her friends saw the incredible benefit a blockchain gave them when recording money. And although they didn’t know it at the time, they only needed a little more information to understand how Bitcoin works. But for now, a mended friendship would be enough.