●●●●● ●●●● ●●0 Caesar Cipher ●●● ●●●● o We can define the transformation as cde f ghijk l m nopgrstuvwxyz D E FGH工了 K LMNOPQRST BO mathematically give each letter a number a bcde f ghijklm 0123456789101112 o p a r st V W x y Z 13141516171819202122232425 o then we have Caesar cipher as C=E()=(p+k)mod(26) p=D(C)=(C-k mod(26) k is the key, which is in the range of 1 to 25. For Caesar cipher, k= 3 COMP4690. HKBUCOMP4690, HKBU 11 Caesar Cipher ⚫ We can define the transformation as: a b c d e f g h i j k l m n o p q r s t u v w x y z D E F G H I J K L M N O P Q R S T U V W X Y Z A B C ⚫ mathematically give each letter a number a b c d e f g h i j k l m 0 1 2 3 4 5 6 7 8 9 10 11 12 n o p q r s t u v w x y Z 13 14 15 16 17 18 19 20 21 22 23 24 25 ⚫ then we have Caesar cipher as: C = E(p) = (p + k) mod (26) p = D(C) = (C – k) mod (26) k is the key, which is in the range of 1 to 25. For Caesar cipher, k = 3