One simple way of coding a message is to mix up the letters in a secret way that only your agent knows. (Your agent is the person you send the message to.)
Suppose we want to say THE ALIENS ARE ATTACKING.
The easiest way to scramble this message is to split it into pairs of letters:
Now we just swap each pair of letters round!
And just to finish it off, we can move the spaces around:
HTA EILN EASER TAA TKCN IFG
Already we've made a nice code, but now we'll make it even better.
The Scramble Grid
This time we'll code a longer message: THE ALIENS ARE ATTACKING TOMORROW NIGHT AT NINE O CLOCK.
Your scrambled message would look like this:
TEAIOITO HNTNRGEC ESTGRHNK AAATOTOU LRCOWACM IEKMNTLR
Finally, to hide how many columns were in your grid, you can move the spaces!
TEA IOIT OH NTN RGECE STG R HNKAAA TOTO ULRCO WA C MIEKM NTLR
If your agent doesn't have a grid, he can still decode your message, so long as he knows your grid had EIGHT rows.