148

Katinka came back into the dining hall with a flushed look and a rosy nose from crying, sending Bjorn and Ante a suspicious look before going over to the couple by the wall. The couple were finished with their meal and ready to pay, which they did with casino tokens that Katinka checked with the same little device that Bjorn had seen used at Nora's place.

"I wonder how that thing works," Bjorn commented, breaking the silence between him and Ante, happy to have something neutral and harmless to talk about.
"What you mean?" Ante asked, munching thoughtfully on pizza.
"That thing to check if the tokens are counterfeit or not," Bjorn explained.
"Ah... well... beats me," Ante said, clearly more interested in his pizza than Bjorn's question. "Does it matter?"
"No... but I'm curious. You know... how difficult is it really to counterfeit those chips?"
"Pretty hard, I would guess."
"But they are just pieces of plastic. Not even very fancy," Bjorn continued, grabbing a few from his trouser pocket and putting them on the table between them.
"No, you're right," Ante agreed, picking up one of the tokens to have a closer look. "But that machine probably makes it harder to fake."
"Exactly! So, how does it work. Aren't you a tiny bit curious?"
"A tiny bit maybe," Ante said, still not looking very interested.

However, the appearance of tokens on their table had caught Katinka's attention, and having just ushered out the other couple, she headed over to them.

"Is everything all right?" she asked. "You're ready for coffee maybe?"
"Well yeah, that would be nice," Bjorn answered without waiting for Ante's opinion.
"And you?" Katinka asked, turning to Ante.
"Yeah, that would be nice," Ante replied.
"Desert too, maybe?"
"Um... no thanks," Bjorn answered, looking over at Ante who nodded in agreement. "But... I was just wondering. Do you have any idea how that thing works? That counterfeit check thing, I mean."
"How it works?"
"Yeah."

Katinka did not answer immediately, and Bjorn got a sinking feeling that he may have touched a nerve again, and that even this seemingly neutral question was a bit much to ask after Ante's interrogation. But just as Bjorn thought he had to back track on his question, or at least moderate it somehow to prevent another scene, Katinka replied that she did in fact know how the device worked.

"It's quite simple actually," she explained with a self conscious smile. "There's an ID chip in each of those tokens. You can easily see them if you hold them up to the light."
"Okay," Bjorn replied, lifting one of his chips up against the light outside. "There it is. But how does that guarantee anything? What if I got hold of a bunch of those chips? Then, what's to stop me from producing as many of these as I want?"
"Exactly. That was what I was wondering too," Katinka replied, happy to be ahead of Bjorn in her understanding.
"And?"
"Well... each chip is registered in a database over at the casino," Katinka explained. "And that's what the device does. It simply calls up the database and checks that the chip is registered there. If it isn't, it's a counterfeit."
"Ah... I see," Bjorn said with a nod, thinking that was the whole explanation. "So I can't just make a bunch of my own tokens."
"No, you can't. Unless you know what ID's are registered in the database, of course."
"Yeah... Of course," Bjorn agreed, realizing that Katinka had just undermined her whole argument. "Even knowing one ID would be enough for me to make a whole bunch of copies, wouldn't it?"

Katinka nodded with a knowing smile, clearly relishing the fact that she had understood this problem and knew its solution.

"Exactly. But the database does more than just check if the ID is registered," Katinka explained. "Because if it only checked the ID, anyone could do what you're suggesting, and we could have like thousands of copies of one and the same chip, all valid in the database."
"So there's a way to prevent that?" Bjorn asked puzzled.
"There is, and it's very simple," Katinka said with enthusiasm.
"Yeah?"
"They use a time stamp."
"A time stamp?" Bjorn asked, puzzled by Katinka's insight. "Where did you learn about this?"
"Well, I was curious. Just like you. So I asked Roger, and he explained a bit. And then I looked it up on the web. You know... to understand it."
"So you know what a time stamp is?" Bjorn asked, still surprised by Katinka's insight.
"Well... It's just the date and time. You know... when things have happened, like."
"Yeah... I know... I was just a little surprised to hear it from you. You talk like an expert."
"Well, thank you," Katinka said with a big honest smile.
"Anyway... so what's with the times tamp."

Katinka made a dramatic pause, not so much to impress the men, but to focus her thoughts into a concise explanation.

"Well, each chip comes with an ID and a time stamp," Katinka said, stressing this point. "Both are stored in the database and in the chip, and both have to match for the chip to be valid."
"Okay," Bjorn said, with growing respect for the young girl.
"The ID never changes, but the time stamp does," she continued, still speaking very deliberately to hammer in the information. "Every time I check a chip, the time stamp is changed in the database and on the chip."
"Yeah?"
"So if you want to counterfeit a chip, you have to copy the ID and the time stamp from an existing chip."
"Yes, right..."
"But the moment either the counterfeit, or the original chip is used and checked with our little device, all the other copies are suddenly having the wrong time stamp and can no longer be used."
"Ah! I see," Bjorn said, seeing dimly how it all works. "So if I take this token, for instance, and make a thousand copies of it with the same ID and time stamp. Then I can still only use one of them. The other ones will become useless the moment I use one, due to the time stamp."
"Exactly. The new time stamp will only match the one we checked, so you can never use more than one token. The other ones become useless the moment one is checked."
"Provided the chip is checked, right?" Bjorn continued. "If I use my counterfeit tokens down at the market, for instance. That may work."
"Yeah. That's true. But if that started happening, even the stall owners would get themselves these counterfeit checking devices, I guess. So far, no one has tried to counterfeit any tokens, though. And as long as the tokens are being checked regularly by some of us, the rest, like the stall owners, can be pretty sure there are no counterfeits in the system."

Bjorn leaned back, totally impressed by the explanation. The girl had figured it all out, and had explained it so well that he was simply speechless.

"So... you want some coffee now," Katinka asked with a satisfied smile.
"Oh yeah. That will be great!" Bjorn answered, looking over at Ante who still seemed to be struggling to understand how exactly the counterfeit checking worked.

Katinka headed for the kitchen and Bjorn asked Ante if had been able to follow what Katinka had said.

"Well... not really," Ante had to admit. "So it has an ID and a time stamp in it?" Ante continued. "And every time the chip is checked, the time stamp is changed?"
"Right," Bjorn said with a smile and a nod.
"And that prevents counterfeiting?"
"Yeah, it does."
"Because the copies will immediately have the wrong time stamp, once one of them have been checked."
"Exactly."
"Well... hey! Maybe I understood it anyway." Ante said with a smile.
"Good for you," Bjorn said with a patronizing grin. "That makes you almost as smart as Katinka."