KidCrypto

August 8, 2006 9:42 PM

Cryptofilter: My daughter is at summer camp and I can snail mail her or I can send email that will be printed out and delivered. The email is fast but readable by whoever prints/delivers the paper etc. Looking for a cipher that would be easy to learn and use...

I would send her the instructions and keyphrase in regular mail then encrypt messages in the email. I want it to be more than a simple substitution but simpler than a one time pad. For fun and learning... any thoughts?

posted by kaytrem to Writing & Language (21 answers total)

You could create a Jefferson wheel cipher.
posted by The Jesse Helms at 9:54 PM on August 8, 2006

ROT13 should work...no one at taking the email off the printer at camp is going to have time or interest to figure it out.

Are they using the Bunk1 system? They sprang that on us a my 11 year old's camp this summer. It worked OK, but we had no idea going in it was going to cost $ (I'm unemployed, and my mother paid for the kid's camp), and then it took a full day off a week's camp to get "approved" to send email...
posted by lhauser at 9:57 PM on August 8, 2006

A simple, but slightly more fun (because its very visual) cryptosystem would be a Rail Fence Cipher (which was actually used by the Spartan military).
posted by gsteff at 10:16 PM on August 8, 2006

Send it as a jpeg and mirror image it in an odd font.
posted by 517 at 10:18 PM on August 8, 2006

Any crypto is going to be a pain in the tail if she gets it on paper. I doubt she's going to be interested in doing the work to try to read it. If you are really concerned about it, I would say that 517 has the right answer.
posted by Steven C. Den Beste at 10:27 PM on August 8, 2006

Send her a large magnifying glass. Then send her a fake letter with your real letter shrunk down to the size of a period and used as a period in the fake letter. Make sure it's not too shiny.

Or, write the letter with a highlighter. The gestapo will wonder why some parts of the paper are more important than others and be unable to read it.
posted by null terminated at 10:40 PM on August 8, 2006

The Arnold Cipher always sounded pretty cool to me.
posted by misterbrandt at 10:45 PM on August 8, 2006

You can work a one time pad by hand fairly quickly. Snail mail her a novel to use as the pad and the instructions in your first email. It isn't CIA secure because the pad isn't random but it's more than enough to keep away the snoopers unless they have a copy of the book, so pick something obscure. Or you could generate an actual OTP.
posted by Mitheral at 10:48 PM on August 8, 2006

I think you're probably better off using some form of simple steganography. You'd want it to be simple enough that it would be really easy to find the hidden text without having to do a lot of calculation or manipulation.

The rule could be something like "circle every word that follows a word ending in -ly" Then you just pad your letter out with a bunch of nonsense words, and slip in an adverb before every word you want to actually communicate with. You could end up with a pretty hilarious sounding 'ciphertext' letter that way, and though it would be really easy to decrypt, no one's going to give it that much attention, since it'll just seem silly.
posted by tew at 11:23 PM on August 8, 2006

My children have the bunk 1 system. I have many issues with it besides the cost. It is really a fax system not email.

Encrypting it is a great idea. On the other hand, I use it to send messages to the camp. I often mention how I do not see pictures and viola, the next day a whole bunch show up. I mention that my daughter is not happy and she gets attention from the counselor. I explained that anyone and probably everyone was reading whatever she wrote. She tried to influence things by saying that she wished there was more ice cream and the like. Not sure if it worked that way.

I wish I had thought to encrypt sooner for the times I really want privacy.
posted by JohnnyGunn at 12:07 AM on August 9, 2006

Any crypto is going to be a pain in the tail if she gets it on paper. I doubt she's going to be interested in doing the work to try to read it.

Why do you think that? I would have thought that a simple cipher was totally fun when I was 10 or 11 (or other ages too), and it will also make each piece of mail last longer.
posted by redfoxtail at 5:11 AM on August 9, 2006

What about an overlay template that has holes for certain places in the text to pass through?

Simply lay it over and read.
posted by StickyCarpet at 5:34 AM on August 9, 2006

I like the idea of using copies of a book as a one time pad (it'd be like Graham Greene's The Human Factor). Otherwise, I have nothing to add except to say you are the coolest parent.
posted by Terminal Verbosity at 6:28 AM on August 9, 2006

If the camp is long enough, and your child enjoys the cyphers, try all of the above. It would take much more effort on your part to distill directions and coordinate snail-mail and email conversations, but I think it wouldn't be too hard for the child to follow if there were stopping points where new cypher instructions were sent secure through snail mail.

Personally I like the adverb idea above. You don't even need to write the article, just find an encyclopedia entry for something funny and boring and sprinkle your message throughout. This sort of thing was used in the movie the Saint (black market contraband messages in marine life message board rants! hee!)

Anyone read "Enigma" (or see the movie?). Or read Cryptonomicon? Fun fun stuff.
posted by cowbellemoo at 7:12 AM on August 9, 2006

lhauser writes "ROT13 should work...no one at taking the email off the printer at camp is going to have time or interest to figure it out."

The problem with ROT-13 is you don't know how savvy the evesdropper is. Text encoded with it is instantly recognisable to anyone with even a little experience with it (the pattern of y's and g's in encypted english text really stands out). Too easy to read even if they don't have a computer; I used to be able to do real time translation in my head.
posted by Mitheral at 7:17 AM on August 9, 2006

The key here is that you have a secure method of transferring info (the snail mail) prior to the encrypted messages. I read your intro, but this is the exact situation that one-time pads are designed for. And how many times in your life do you actually get to use a OTP?

Although, StickyCarpet's overlay template seems the quickest and easiest method to use.
posted by jsonic at 7:59 AM on August 9, 2006

I work for a camp that delivers correspondence by the same kind of system (your choice of secure but slow snail mail vs. quick but open e-mail). We don't open or look at sealed snail mail at all; we scan e-mail not really for security reasons, but more because hey, it's on the screen, what else are you going to look at? And if we see something unusual when we glance, we keep reading. That's human nature, and I'm sure sorters do the same thing with postcards.

I wouldn't care about nonsense text or anything that appeared to be inside jokes; this is probably your best bet. Something that seems to make sense on the surface, but also has a hidden layer of meaning, is perfect. You can tell your daughter in advance to look at every fifth word for the secret message, or you can work out double meanings in a letter ("if you e-mail me back saying you saw a crow, that means you're unhappy"). I'm sure this will also be easiest/fastest for your daughter.

If I received an obvious hash of numbers or nonsensical letters, I would try to work out just enough to be sure it didn't say "Blow up the camp now" or "Have you sold all the drugs yet?" Well, okay, I'm kidding about those -- but camps have to deal with a ton of custody issues, and we'd all hate to have a noncustodial parent secretly work out a deal to pick up a kid. It's happened before, to other camps, and everyone's panicked it'll happen here.

If I couldn't work out an e-mail that was an obvious cipher -- say, if it was based on a book or on prior instructions sent by mail -- I would definitely ask a superior. I'm not sure what we would do, but probably the next step would be asking the kid, casually, if she would translate the first 10% of the e-mail, or a sentence we'd pick randomly, or something else that would assure us the content wouldn't be our business.

In short, make your system not obviously gibberish if you want it to pass unexamined. We would investigate not to be snoopy, but to make sure we wouldn't opening ourselves up to all kinds of trouble. I think the e-mails should be as private as the sealed snail mail, and I would love it if my parents had been as cool when I went to camp as you are, but we really, really can't let ourselves get in the middle of custody battles.
posted by booksandlibretti at 8:02 AM on August 9, 2006

Considering she will need both pieces of mail/email why not put every other word in each document. The casual snooper won't bother or he'll think its some silly mad libs. Your daughter can just piece the two together. No wasted hours doing crypto by hand. Skilling and I used to do that in the old days.
posted by the ghost of Ken Lay at 8:08 AM on August 9, 2006

a really great site full of javascript crypto tools and explanations run by a guy who's incredibly helpful and more than willing to get involved in a long email correspondance about your particular crypto problem.

(I speak from experience; he and I corresponded for weeks about one time rings.)
posted by dmd at 8:38 AM on August 9, 2006

A lot of crypto is tedious to decrypt by hand. I'd recommend really lame steganography, e.g., every 5th word counts, or the first word in each line (problematic if their email client doesn't preserve line breaks.)

Plaintext: Your sister and I went shopping today.

Ciphertext:
Your cat misses his little
sister who got lost yesterday
and he started meowing wildly --
I made posters and then
went to hang them but
shopping carts totally stopped me
today.

(Linebreaks provided for readability -- don't leave them in the finished product.)

This also lets you be silly in the ciphertext and provide some extra entertainment.
posted by Zed_Lopez at 10:15 AM on August 9, 2006

I have no idea. But what a cool idea!
posted by radioamy at 6:36 PM on August 9, 2006