Make a Language!

By far better than codes, languages make it much harder to crack your secret messages, and you can use them out loud. But learning French or Spanish might backfire, as other people know them. So why not make one that only you and your trustworthy associates know? This is a great help, though last time I checked the server was down. Wikihow has several helpful articles. I suggest looking at a couple and combining them.

Math is Useful (Finally!)

Ever heard of a spirolateral? All you need is graph paper, the handy chart shown above, and a variety of markers. First write your word (or message) and translate it into numbers. Put the numbers (in the right order, of course) into the above chart. Now pick a spot in the middle of your graph paper and move in whatever direction the number tells you, counting the spaces for however long. You might want to switch colors between words, or, if you're doing one word, repeat it a couple times (four works best). Remember to make the place where you started out inked heavier than the rest of the code.
How do you decode it? It's up to you.

Further Encoding Codes

There are plenty of other ridiculously easy ciphers to use. Unfortunately, they are also easy to crack, so here are some ways to make sure your message can only be understood by you and the person it is being sent to:

If you are using a cipher in which you replace letters with other letters or symbols, don’t use spaces or &T**U OECI&PTU can be translated into HAPPY BIRTHDAY with a bit of time and thought. You know that one is a five-letter word that way, and the other is a eight-letter word. You can also tell that the last letter is the same for both. So use a symbol or letter (and not a dash or underscore) for a space instead. If you like you could even add extra spaces to throw someone off the trail.

An easy trick is to use a different word for some words and agree on them with whoever will be using your code. For instance, to say MEET ME ON FRIDAY you could say MEET ME AT A RESTAURANT and your friend would know to meet you on Friday (if you were meeting at a restaurant, you’d most likely tell which one, right?)
You can also use floriography. If you wanted to reply to an invitation discreetly, you might write STRIPED CARNATION, which means ‘no’.
While you’re looking, you might want to see what a green rose means.

The Ivy Cipher

The ivy cipher goes as follows. First, you write down your message (as per obvious) like so:

GET TO THE RACETRACKS IMMEDIATELY.

(I write really random messages when I want to). Now you write all of the words so they are backwards, getting rid of pesky punctuation as you go.

YLETAIDEMMISKCARTECAREHTOTTEG.

Now put them into two rows with every other letter:

YEADMIKATCRHOTG
LTIEMSCREAETTE

Now you have the ivy cipher. You may want to put the word ‘ivy’ inside the code somewhere, or some other codeword signifying that that’s how you make sense of it.

#2 'A Bold Code'

Please excuse the lame pun, but this code involves using a bold font (or retracing the letters so they are bolder if you are writing). First you need to come up with a code. Below I have one. The stars are for none-bold print, the B's are for bold letters.

A=***** G=**BB* M=*BB** S=B**B* Y=BB***
B=****B H=**BBB N=*BB*B T=B**BB Z=BB**B
C=***B* I=*B*** O=*BBB* U=B*B**
D=***BB J=*B**B P=*BBBB V=B*B*B
E=**B** K=*B*B* Q=B**** W=B*BB*
F=**B*B L=*B*BB R=B***B X=B*BBB

Now let's say I wanted to tell my friend 'I have your book.' First I need to write a long and pointless message I can fit my code into. Since I have thirteen letters in my message, I need to multiply that by five to get a code that needs sixty-five letters or more.

The math homework is pages sixteen to twenty-seven, but only the even problems. I suggest you do the odd ones because you can check your work in the back.

Punctuation can count, but you can't tell if a space is bold, so just get rid of those in your head.

The math homework is pages sixteen to twenty-... and so on. Be warned this code takes a while or I would have done the whole message. It's also hard (for me) to keep track of which letter you're on.

SDCOE

There comes a time when anyone (well, anyone with an interesting life) would benefit from the use of codes. There are some codes like pig latin that are easy to decipher, and others that are really hard.
For the next couple weeks (or just one, depending on how many codes I find) I'm going to be talking about the second of the two types of codes.

#1 The Box Code.

This is a code in which you'll write your message in a box. For example, I'll encode 'Meet me after school in the gym.' You now have to count the letters to find what size square you'll be using. In this case there are twenty-five. In the case that your message doesn't have a perfect square for the number of letters, use a 'dummy' letter to fill in the extra space. Now I know to do a five-by-five box.

MEETM
EAFTE
RSCHO
OLINT
HEGYM

It doesn't have to look like a square. Now you go down the rows and write what it says.

MEROHEASLEEFCIGTTHNYMEOTM.

You can add spaces randomly throughout the message if you want to. Now you give it to your friend. They'll count the number of letters and can put it in the same square, this time writing the letters down in columns.

*WARNING* Make sure your friend KNOWS about the code or they'll have just as much trouble deciphering it as They Who May Not Read The Message.