Their parents weren't really enthusiastic about the idea of Anne refusing to use communication channels any more modern than mail transported by railroad, but they had to live with it anyway. They were used to knowing about all the details about what's going on with he kids, so they were eagerly expecting the (previously not extraordinarily popular) postman.
The siblings' dad was working for a big oil conglomerate, while their mom planned inbound trips for tourists at a travel agency. They were just as glad to see a chance for Anne finally returning to the normal, real world. Actually, they felt it wasn't even such a huge issue that she hadn't called them yet, as her classmates don't talk to their parents too often anyway, either... but it'd still be good to know how she's doing. The usual schedule (huge dinner, then watching TV) was thus being interrupted by digging through the contents of the mailbox, lately, without much success so far.
It's been three days since the camp started. Akos (straight from driving practice) and his parents (from work) arrived at just about the same time; of course, the worried mom beelined towards the mailbox right away. And yes! Anne has written something, at last. She didn't rush opening the envelope; she shall present it to the entire family later. They'll get to see how much their daughter has improved in terms of social skills. She'll surely let them know how much fun she's having with her classmates... well, let's see.
It was a fancy piece of stationery, folded in two. Akos was observing the scene with much interest. Mom has a look at it... there is obviously something wrong with that letter... she shows it to Dad, then takes it back... Akos is smiling. The outcome of his sister getting into writing letters is expected to be at least as much out of the ordinary than everything else she does, he could have predicted this ahead of time.
"What do you think this is?," they handed him the mysterious piece of paper. All it had on it was two lines of text and a huge pile of numbers. Well, it was supposed to be a math camp, after all... "Hi all! Camp is super cool! This one below is RSA cipher, we just had a class on it today. Feed it a computer to crunch through!" Well, apparently, her little sister still hadn't drunk enough beer yet...
Akos spent the rest of the day studying the RSA cipher and writing code breaking programs, while his parents, in place of watching TV even, were arguing over what exactly went terribly, terribly wrong during their daughter's upbringing.
The code-breaker program was ready by later in the evening and doing the calculations all night. He just passed out on his bed, still wearing the previous day's outfit... but at least he successfully avoided the turmoil raging downstairs. He didn't dare to take sides... actually, he didn't know either what the right answer was. Nevertheless, he wasn't entirely caught off guard by the idea. After all, Anne and the concept of an average, unambiguous, easily readable piece of mail, consisting of nothing else but letters, just didn't fit.
The program had printed the decoded text already. She surely transformed the original using her programmable calculator: encryption took much fewer calculations (that's the point of encryption, after all). But even so, she still needed quite an amount of free time... he started reading the few lines that showed up on-screen:
"encryption is super cool, camp lkwise. laci n gang r idiots. 2 bad u didnt come. mom and dad surely loved encr too? ;) Anne"
It wasn't much, but revealing quite a lot. He imagined the scene: Anne tinkering with her calculator on the top of her bunk bed, thinking about all the math, with her usual enthusiasm, partly since she just finds it interesting, but also because she doesn't fit in with her classmates who are chatting underneath, having fun (making fun of her probably included). Poor her.
He spent the entire day in a gloomy mood because of this. In the end, he came up with the idea of writing a reply to her, encoding it with her private encryption key (that he now knows anyway), and sending it to her over the mail. Sometimes she needs a bit of encouragement too. In fact, he could just modify the code a bit, and...
"they were extremely pleased with it ;) nothing's up here. dont do too much math though. laci doesnt matter. all sides of the world are simple, just try. akos"
The letter was sent out the same day, priority, first-class, whatever it takes. It'd be there by the next day. He put their math teacher as the recipient, she'll surely give it to her. With that having been done, he started feeling a little better.
Another three days passed. Their parents were presented with a slightly modified version, her last sentence having been changed to "say hi to mom n dad", just to avoid further compliations. Apparently, they've already given up on debating the question again and again.
He also stayed silent about the encrypted response. Nevertheless, they kept sifting through the mailbox regularly, which did indeed not prove futile.
Opening the second mail was less of a special and important event compared to last time; they were already prepared for everything. Akos wasn't even present for the occasion, so he was even more surprised, coming home, that the letter waiting for him wasn't all numbers this time. On the contrary: he arrived to a surprisingly upbeat mood.
"Anne finally wrote a sane mail, too! Want to have a look?"
Of course he wanted to. It's surely only him who can crack the code anyway, he thought, but, apparently, the writer of the letter was more considerate this time and had hidden it behind the normal-looking text. Yet another challenge! He climbed upstairs to read it. No wonder it was longer than the last one: one needs more filler text to hide content in.
"Hi everyone! I hope you're all well, and you aren't coming home as late as you usually do. We are having lots of fun here, there are lots of math classes, with stuff sometimes not even I understand. And lots of cool people! Will go home soon. Hugs to everyone! Anne"
Akos spent another evening cracking codes, but he was out of luck this time. He tried three kinds of encoding schemes, of course by using the computer... nothing. But then... what if she used some special marks on the letters? He kept trying till midnight, before giving up. Of course, it's possible that there isn't any encryption scheme to crack... but then why is she writing such... dull mails? Using "lots" three times in three sentences? Sure, she might have wanted to write something more readable than RSA cipher, but even so, she wouldn't have to be so bland. Or... maybe this was the result of her drinking some beer, finally? Must be that... he'll get to know soon anyway. She was to come home the next day.
The entire family showed up to fetch her from the train station. With more than ten minutes before their scheduled arrival, they were pacing up and down on the platform, to make sure they wouldn't miss a thing. Akos was staring at the "end" of the tracks fading into the horizon, where the train was supposed to show up. There was another train heading out from the neighboring platform right then, the resulting rumble drowining out their voices.
The "math camp" train rolled in two minutes late. The locomotive drew down its pantograph, the huge motors started to slowly wind down. The cars disgorged large crowds of people, most of whom quickly dispersed, bustling towards the various gates of the station. A larger group started accreting near the far end of the train; the family set off that way, too. Yes, it's them!
Anne was deep in a conversation with two other girls, most likely some of her classmates? The rest of the family was cautious not to take a chance disturbing this rare and unusual occurrence, so they approached the math teacher instead, "thanks a lot for organizing this wonderful camp, Anne surely learned a lot" and so on.
"Well, yes, she put in a solid amount of work at the start of the week. She ended up preferring talking to the others instead, towards the end, though... but I didn't mind, she had done just enough math already."
"We're glad to see that she can barely detach herself from her friends... we got a letter from her that only her brother could decipher, but the next one was fortunately readable even for parents like us..."
"Yes, she really liked the class on encryption... well, excuse me, it's a pleasure talking to you but I must escort the middle schoolers to the school building..."
"Of course, we wouldn't like to hold you up. Thank you again!"
The teacher left with a largeish group of kids, while they kept waiting patiently for Anne to finish the conversation. Which didn't go too easily: one of her classmates took out a pile of CDs of her bag, which were promptly tucked away in Anne's. It took quite a few minutes for her to notice them eventually.
"Hi!!! Sorry for having chatted so long, but it was sooo interesting. Camp was so awesome!"
"Good to see you, finally! So, how was it?" her parents clinged upon every one of her words.
"Weeell... it was the second half that was really good, I was way too much into math during the first part, but not towards the end. Like, even my classmates are kinda... cool? We went and tried some beer, a bit, it doesn't even taste that bad, actually... but I'll start from the beginning... or the middle, nothing interesting happened until the middle, anyway... so, Akos, you'll surely appreciate this: it was Laci who came up with this idea of, that I'm so lonely (not that I was!), and that I should see how the... "real world" looks like, because the only thing I'd seen so far was math. They were, actually, right after all, but I didn't believe them back then. I was like, if they really want this so much, then sure, I'll go and check out the pub with them, just so that can win all the debates about it. But I really don't know why they're so nice to me recently, Laci for example, he told off everyone who was calling me "extraterrestrial"... they even let me taste their beer!"
"But you surely haven't drunk too much?"
"Yeah no, tootally not too much... so, then, when we got back from the pub, Angie and the other girls, the ones you've just met, explained to me which DJ was the coolest, they even had a pair of speakers that they brought to the camp, and... what they're listening to wasn't... that bad, actually? So, I realized that math was so interesting only because I didn't know how interesting the rest of the world was! It's just too bad that I'm not so good at it anymore because I don't care so much."
"Don't worry, you're just feeling that way because you weren't even trying too much this time. Which is commendable."
"All right then! I don't think it's a bad thing either. So... like... and it's not just that everyone is suddenly nicer but they aren't as... boring anymore as they used to be? But they're talking about the same stuff, actually, but... in a different way somehow? And now it's much more interesting?"
"See? We were always telling you, all it takes is actually talking to your classmates!"