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A note has been left giving information to help you but to read it you need to first crack the code. Just to make it harder one of the words might be an.

Y 59, 32, 13, 59, 37 __ 60, 82, 30 __ 59, 19, 80, 30! The table is a grid showing the numbers from 1 to 100, although some of the numbers have been replaced by letters. The children should look at the first number in the code, find where it should be in the grid, and write down the letter that is in its space. Repeating this process should enable the children to work out the code. All of these codes can be used as a Maths activity. For example, the message for the table above can be replaced.

50+9, 8x4, 10+3, 60-1, 40-3 __ 6x10, 80+2, 10x3 __ 50x9, 20-1, 20+20+20+20, 15x2! The children should therefore work out the answer to each of the sums (e.g. 50 + 9 = 59) and then continue as before.

March 2005 'Few persons can be made to believe that it is not quite an easy thing to invent a method of secret writing which shall baffle investigation. Yet it may be roundly asserted that human ingenuity cannot concoct a cipher which human ingenuity cannot resolve.' Edgar Alan Poe - 'A few words on secret writing'; 1841 Human desire to communicate secretly is at least as old as writing itself and goes back to the beginnings of our civilisation. Methods of secret communication were developed by many ancient societies, including those of Mesopotamia, Egypt, India, China and Japan, but details regarding the origins of cryptology, i.e.

The science and art of secure communication, remain unknown. Classical cryptography. The scytale We know that it was the Spartans, the most warlike of the Greeks, who pioneered cryptography in Europe. Around 400 BC they employed a device known as the scytale. The device, used for communication between military commanders, consisted of a tapered baton around which was wrapped a spiral strip of parchment or leather containing the message. Words were then written lengthwise along the baton, one letter on each revolution of the strip.

When unwrapped, the letters of the message appeared scrambled and the parchment was sent on its way. The receiver wrapped the parchment around another baton of the same shape and the original message reappeared. In his correspondence, Julius Caesar allegedly used a simple letter substitution method. Each letter of Caesar's message was replaced by the letter that followed it alphabetically by three places. The letter A was replaced by D, the letter B by E, and so on.

For example, the English word COLD after the Caesar substitution appears as FROG. This method is still called the Caesar cipher, regardless the size of the shift used for the substitution. Simple substitution ciphers are easy to break. For example, the Caesar cipher with 25 letters admits any shift between 1 and 25, so it has 25 possible substitutions (or 26 if you allow the zero shift). One can easily try them all, one by one. The most general form of one-to-one substitution, not restricted to the shifts, can generate 26!