If the message is intercepted and if the enemy can figure out what you are up to, your cover will be blown and your mission will be lost. It may seem odd at first, but the key to getting information from one person to another securely is a little bit of shared knowledge. Codes One of the safest ways of sending information is in code form which relies on both the sender and the receiver having the 'key' which unlocks the code. Even if a coded message is intercepted, it will take time to be cracked and by then it might be too late for the information to be of any use. A simple way of encoding a message is to make a code wheel. For this you need paper, scissors, two split pins and a pen. You need to make two wheels, each with the same code so it might be useful to make both at the same time. For each code wheel cut out two circles of paper, one 10 centimetres across and the second 12 centimetres across. In the smaller circle cut a small 1cm2 window, about 3 centimetres from the centre. Attach the two circles together at their centres using the split pin so that the small circle can turn over the second larger circle. Write the alphabet around the edge of the large circle. Draw an arrow on the small circle, pointing to one of the letters on the large circle. Now onto the code itself. Turn the small circle until the arrow points to the letter 'a'. Write a letter which you want to represent 'a' in your code in the centre of the window - let’s say you choose 'g'. Make a note on another piece of paper that this letter has been used up. (it makes it easy if you make it a two person job, one writes in the two wheels, the other reads off an alphabet, ticking the random letter choices off as they go along!) Then turn the wheel so the arrow points to 'b'. Write another letter in the centre of the window, say 't'. Do this for all the letters in the alphabet. Once your wheel is complete you can start to encode your message. Everywhere there is an 'a' in your message you write the letter you see in the centre of the window, in this case 'g'. Where there is a 'b' you write 't' and so on. For your ally to decode your message, they need to use the second code wheel. Turning the small circle so that the first letter of the coded message appears in the window (‘g’), the arrow will point to the first letter of the real message (‘a’). If you don't want to use letters in your code you can use symbols instead - or if you have enough colours you can try these! Remember, the less your message looks like meaningful information the less likely you are to get caught out. Be careful not to let your code wheel fall into enemy hands. Not only will they be able crack your code and find out what you are doing, you may never even know that they know! If you are very unlucky they may feed you false information. . Today making and breaking codes is big business - not just for spies but for everyone who wants to buy or sell something over the internet. Coding material today is known as encryption and it involves scrambling the data randomly. When the information is sent over the internet only people who have the 'key' to unlock the code can see the real data - everyone else sees rubbish. Invisible Messages Even if you haven't agreed on a code beforehand you can still receive a secure message. It requires some shared information but not nearly as much as for a code. To make an invisible message you need a piece of paper, a cotton wool bud and some lemon juice. Squeeze the lemon to make it more juicy, cut it in half. ake the cotton wool bud and dip it in your lemon juice. The juice is the ink, use the bud and write your instructions on the piece of paper. While it is wet it is still visible. To read the message, run it over with a hot iron. Be very careful not to burn yourself or the paper! Slowly you will see the message emerge. How does it work? The lemon juice is very nearly clear so does not show up on the paper when it is dry. When you heat the lemon juice it starts to burn. Like all organic material, anything that was once living, the lemon juice contains carbon. When it burns it releases some of the carbon in the same way a candle releases soot. The brown writing is just the carbon that has come out of the charred lemon juice. You can try this with other organic compounds like milk. Today inks are available which can only be seen under ultraviolet light. Under normal light the message is invisible but under ultraviolet light all becomes clear! These inks absorb ultraviolet light and reemit normal light that we can see, so they appear to glow. receiving your instructions • gathering information • reporting back • spy box menu