circusmonkey404's Security Site

Krypton 4 Objectives You more than likely used some form of FA and some common sense to solve that one. So far we have worked with simple substitution ciphers. They have also been ‘monoalphabetic’, meaning using a fixed key, and giving a one to one mapping of plaintext (P) to ciphertext (C). Another type of substitution cipher is referred to as ‘polyalphabetic’, where one character of P may map to many, or all, possible ciphertext characters. An example of a polyalphabetic cipher is called a Vigenère Cipher. It works like this: If we use the key(K) ‘GOLD’, and P = PROCEED MEETING AS AGREED, then “add” P to K, we get C. When adding, if we exceed 25, then we roll to 0 (modulo 26). P P R O C E E D M E E T I N G A S A G R E E D\ K G O L D G O L D G O L D G O L D G O L D G O\ becomes: P 15 17 14 2 4 4 3 12 4 4 19 8 13 6 0 18 0 6 17 4 4 3\ K 6 14 11 3 6 14 11 3 6 14 11 3 6 14 11 3 6 14 11 3 6 14\ C 21 5 25 5 10 18 14 15 10 18 4 11 19 20 11 21 6 20 2 8 10 17\ So, we get a ciphertext of: VF