1. CAP Cryptographic Analysis Program Homophonic Cipher Help Presentation Press Enter or click on your mouse button to continue

2. Use the mouse button to activate each presentation step 2 Homophonic Cipher This is a cipher that assigns more than one number to each letter It randomly selects one of the assigned numbers to replace the letter in the ciphertext

3. Use the mouse button to activate each presentation step 3 Process A four letter keyword is selected such as “next” The numbers from 1 to 100 are arranged into four groups of 25 numbers (1-25,26-50,51-75,76-100) The numbers assigned to each letter are determined by assigning the first letter of the key word to the first number in each group and then cyclically assigning the rest of the letters to the numbers in each group For example: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 n o p q r s t u v w x y z a b c d e f g h i k l m 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 e f g h i k l m n o p q r s t u v w x y z a b c d 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 x y z a b c d e f g h i k l m n o p q r s t u v w 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 t u v w x y z a b c d e f g h i k l m n o p q r s Note: j is left out

4. Use the mouse button to activate each presentation step 4 Example Key The example key from the prior slide results in four numbers assigned to each letter 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 n o p q r s t u v w x y z a b c d e f g h i k l m 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 e f g h i k l m n o p q r s t u v w x y z a b c d 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 x y z a b c d e f g h i k l m n o p q r s t u v w 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 t u v w x y z a b c d e f g h i k l m n o p q r s For example “a” can be replaced by 14, 47, 54, or 83 The cipher randomly selects one of the four numbers each time “a” appears in the plaintext