Vigenère
An improved code was developed by Vigenère, where a different row is used for
each character encryption, and is polyalphabetic cipher as it uses a
number of cipher alphabets.hen the way that the user
moves between the rows must be agreed before encryption. This can be achieved
with a code word, which defines the sequence of the rows. For example the
codeword GREEN could
be used which defined that the rows used were: Row 6 (G), Row 17 (R), Row 4 (E),
Row 4 (E), Row 13 (N), Row 6 (G), Row 17 (R), and so on (see Table). Thus
the message is converted as:
Keyword GREENGREENGREE
Plaintext hellohowareyou
Ciphertext NVPPBNFAEEKPSY
The following should be able to determine the code for a given phrase and key:
Enter phrase:
Enter key:
The code is:
Try a phrase of "hellohowareyou" and a key of "green", and you
should get:
NVPPBNFAEEKPSY
Plain 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
1 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 a
2 c 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
3 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
4 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 d
5 f g h i j k l m n o p q r s t u v w x y z a b c d e
6 g h i j k l m n o p q r s t u v w x y z a b c d e f
7 h i j k l m n o p q r s t u v w x y z a b c d e f g
8 i j k l m n o p q r s t u v w x y z a b c d e f g h
9 j k l m n o p q r s t u v w x y z a b c d e f g h i
10 k l m n o p q r s t u v w x y z a b c d e f g h i j
11 l m n o p q r s t u v w x y z a b c d e f g h i j k
12 m n o p q r s t u v w x y z a b c d e f g h i j k l
13 n o p q r s t u v w x y z a b c d e f g h i j k l m
14 o p q r s t u v w x y z a b c d e f g h i j k l m n
15 p q r s t u v w x y z a b c d e f g h i j k l m n o
16 q r s t u v w x y z a b c d e f g h i j k l m n o p
17 r s t u v w x y z a b c d e f g h i j k l m n o p q
18 s t u v w x y z a b c d e f g h i j k l m n o p q r
19 t u v w x y z a b c d e f g h i j k l m n o p q r s
20 u v w x y z a b c d e f g h i j k l m n o p q r s t
21 v w x y z a b c d e f g h i j k l m n o p q r s t u
22 w x y z a b c d e f g h i j k l m n o p q r s t u v
23 x y z a b c d e f g h i j k l m n o p q r s t u v w
24 y z a b c d e f g h i j k l m n o p q r s t u v w x
25 z 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
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