# secretcodes tcm4 336597

Published on December 31, 2007

Author: Sudiksha

Source: authorstream.com

Slide1:  Ever wanted to send a message but not let anybody else know what you are saying? For thousands of years people have been doing just that. They do it using codes. Slide2:  The ancient Egyptians and Greeks used codes to create secret messages. Mary Queen of Scots sent letters in code. During World War II the Nazis used the Enigma code machines to encipher their messages. Allied mathematicians and cryptographers worked on breaking the Nazi secret codes. They were able to build replicas of the German Enigma machine which they used to decipher Nazi radio messages. Enigma Machine Slide3:  One of the easiest codes you can use is the ‘alphabet up one’ code. This is when you want the letter A but use the letter B instead. If you want B, you would use C. For C - use D and so on up until Z which moves up one to become A. Slide4:  Here is a grid to explain how the code works: A B C D E F G H I B C D E F G H I J J K L M N O P Q R K L M N O P Q R S S T U V W X Y Z T U V W X Y Z A If you break this code - ZPV XJMM VOEFSTUBOE UIJT NFTTBHF Slide5:  You can use the ‘alphabet up two’ code or the ‘alphabet back one’ code. You can use any code you like as long as the person receiving the message knows what code you are using. You should make a grid for the ‘alphabet up two’ or the ‘alphabet back one’. When you have done this, you should write a message for a friend. See if they can understand what your coded message says. Slide6:  Another famous code is the ‘numbers for letters’ code. In this code we use 1 instead of A, as A is first in the alphabet. We use 2 instead of B, as B is second in the alphabet….. and so on all the way up to 26 instead of Z, as Z is the twenty sixth number in the alphabet. 3 - 1 - 14 25 - 15 - 21 6 - 15 - 12 - 12 - 15 - 23 20 - 8 - 9 - 19 Slide7:  If you make things really difficult for codebreakers, you can combine the two codes and do the ‘alphabet up one + numbers for letters’ code. Instead of A we use B …. but B is second in the alphabet, so A becomes 2. B moves up one to C but C is third in the alphabet and so on. This is not easy, so the best thing to do is write out a grid. A B C D E F G H I 2 3 4 5 6 7 8 9 10 J K L M N O P Q R 11 12 13 14 15 16 17 18 19 S T U V W X Y Z 20 21 22 23 24 25 26 1 Notice that Z moves up in the alphabet to A, so becomes the number 1 Slide8:  Playing with codes is great fun. Be careful that you don’t make up a code that is so difficult to break that nobody can work out what you are saying. REHTONA SUOMAF EDOC is the back to front code. This is where the words are all spelled back to front. If I want to use the word SPY, I reverse the letters and get YPS. Slide9:  If you are really good with codes, you can do complicated things like replace the letters of the alphabet with numbers but do it in reverse order. Slide10:  A is the first letter of the alphabet but we will use the number 26 B is the second letter of the alphabet but we will use the number 25 We continue this pattern all the way up to the letter Z Z is the twenty sixth letter of the alphabet but we will use 1 A B C D E F G H I 26 25 24 23 22 21 20 19 18 J K L M N O P Q R 17 16 15 14 13 12 11 10 9 S T U V W X Y Z 8 7 6 5 4 3 2 1 12 – 13 – 15 – 2 22 – 3 – 11 – 22 – 9 – 7 – 8 24 – 26 – 13 24 – 9 – 26 – 24 – 16 7 – 19 – 18 – 8 24 – 12 – 23 - 22 Slide11:  Squared number codes: Do you know your squared numbers? If you square the first ten numbers, you get: 1 4 9 16 25 36 49 64 81 100 Can you tie squared numbers to the letters of the alphabet to create the squared number code? A = 1 B = 4 C = 9 … Slide12:  A B C D E F G H I 1 4 9 16 25 36 49 64 81 J K L M N O P Q R 100 121 144 169 196 225 256 289 324 S T U V W X Y Z 361 400 441 484 529 576 625 676 400 – 64 – 25 16 – 81 – 196 – 196 – 25 – 324 144 – 1 – 16 – 625 81 – 361 1 361 – 256 – 625 Slide13:  Although this looks quite difficult, the first thing a good code breaker would notice is that all the numbers are squared numbers. When you spot this, breaking the code becomes much easier. The first thing a good code breaker looks at is the set of numbers and if they can spot that all the numbers are even, odd, squared, prime or members of any other set of numbers, they know where to start when breaking the code. 28 – 30 – 46 26 – 2 – 22 – 10 50 – 30 – 42 – 36 30 – 46 – 28 6 – 30 – 8 – 10 – 38

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