"The history of codes can be traced back to ancient Greece. Codes are a way of sending secret messages so that only the people sending them and the people receiving them can read them. Behold, the mother of all codes, the skytale! Skytale (rhymes with Italy) is Greek for 'stick' and here's how to make one."

• Cardboard tube from a roll of paper towels
• Strip of paper about a half-inch wide
• Tape
• Pen or pencil

1. Tape one end of your strip of paper to the end of the tube.
2. Wrap the paper at an angle completely around the tube and tape the other end. (You may have to tape two or more strips of paper together to make the strip long enough.)
3. Now carefully print your message on the paper from one end of the tube to the other.
4. Remove the paper from the tube.

"Now you have a strip of paper containing a bunch of letters that don't make sense to anyone who doesn't know how to wrap the paper around their own tube! Y'see, the message on the paper doesn't mean anything UNLESS you wrap it around a stick - or in this case, a tube - exactly the same size as the one it was written on!"

"But, Beakman, what if you want to send a secret message and your dad won't let you use the paper towel tube 'cause he needs it for his paper towel tube collection? What do you do, huh? Huh?"

"I've got just the thing for you, Liza. A grille!"

"Now you're cooking! Let's barbecue!!"

"No, Lester. A grille."

• Several 3-inch by 5-inch file cards
• Ruler
• Scissors
• Pen or pencil

1. Cut six small rectangles out of a file card. Space them randomly, not too close together.
2. Cut a little of the top, left-hand corner off, so you know that's the top of your grille.
3. Cut another card exactly the same way, so the person to whom you're sending secret messages has a matching grille. You can use your card as a guide to trace matching holes onto another card.

"So far, all you got is a couple of moth-eaten index cards. You can see right through them! Where's the intrigue? Where's the mystery?"

"Quell your queries, Lester. All will soon be revealed."

4. Take your grille and place it on top of another blank card.
5. Write your secret message in the holes.
6. Remove the grille and write a longer message on the card around the words that are already there. Try to make the longer message make sense.
7. Send your friend the card. Then he or she can use the matching grille to decode-code your secret message!

"Putting messages into code is the science I like to call 'cryptography.' From the Greek words 'kruptos' - meaning hidden or secret - and 'graphein' - meaning to write. Codes are cool. They can involve mathematics and computer science. Codes were used in ancient Greece for the same reason they're used now - to send secret political and military information."

Cryptanalysts are experts in solving ciphers or cryptograms. A cipher or cryptogram is a coded message. There are two basic kinds of codes: transposition and substitution.

A transposition code involves transposing or mixing up the letters of the message in some systematic way. The codes in this activity are two examples of transposition codes.

In a substitution code a different symbol (letter, number, or picture) is substituted for each letter of the alphabet. To make this kind of code more difficult to crack, each letter can be given more than one symbol. Julius Caesar used a very easy substitution cipher. He simply substituted the third letter in the alphabet after each letter in his message. In our alphabet this would mean that "A" would be encoded as "D", "S" would be encoded as "V" and so on. Obviously, a cryptanalyst would have no difficulty deciphering such a simple cipher.

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