Question

2- Plain Text (Message):

a) JERSEY

b) CALIFORNIA

Key: CSEC

Scheme: Vigenere Cipher

Cipher Text:

Answer 1

• The encryption of the original text is done using the Vigenère Table. This table consists of the alphabets written out 26 times in different rows, each alphabet shifted cyclically to the left compared to the previous alphabet. For easy understanding below is the image of Vigenère table.

PROCEDURE FOR GENERATING CIPHER TEXT

• For the encryption process, we uses a different alphabet from one of the rows for every character of our Plane Text, and also the alphabet used for encrypting each character depends upon the key.
• Be sure, length of key must be equal to length of plain text, if it is not then the given keyword is repeated in a circular manner unitl it matches the length of plain text.
• Once we have generated our key properly, we can procced to encrypt every character of plain text one by one.
• For encrypting a character we have to select a character from the table, and this selection of character is dependent upon both character of plain text as well as corrsopondind character of the key.
• Plain text character is used to select the Row, while key is used to select the Column of the Vigenère Table.
• This is what we have to do for every character of the Plain text and text formed by the combination of character selected from Vigenère Table for each character of plain text will be the resulting Cipher Text.

DETAILED SOLUTION

• Answer / Explaination a)
  • Plain Text - JERSEY
  • As mentioned above our key length must be equal to that of plain text length. So, our resulting key will be CSECCS.
  • Key - CSECCS
  • Cipher Text - LWVUGQ
  • First Character of Plain text 'J' is paired with first character of key 'C'. So, 'J' row and 'C' column is selected and the value in the Vigenère Table is 'L'.
  • Second Character of Plain text 'E' is paired with second character of key 'S'. So, 'E' row and 'S' column is selected and the value in the Vigenère Table is 'W'.
  • Third Character of Plain text 'R' is paired with Third character of key 'E'. So, 'R' row and 'E' column is selected and the value in the Vigenère Table is 'V'.
  • Fourth Character of Plain text 'S' is paired with fourth character of key 'C'. So, 'S' row and 'C' column is selected and the value in the Vigenère Table is 'U'.
  • Fifth Character of Plain text 'E' is paired with fifth character of key 'C'. So, 'E' row and 'C' column is selected and the value in the Vigenère Table is 'G'.
  • Sixth Character of Plain text 'Y' is paired with sicth character of key 'S'. So, 'Y' row and 'S' column is selected and the value in the Vigenère Table is 'Q'.
  • Thus Cipher Text will be LWVUGQ.

• Answer / Explaination b)
  • Plain Text - CALIFORNIA
  • As mentioned above our key length must be equal to that of plain text length. So, our resulting key will be CSECCSECCS.
  • Key - CSECCSECCS
  • Cipher Text - ESPKHGVPKS
  • Following the same steps as we have used in the above answer will we generate cipher text.
  • First char from plain text - 'C' (row), first char from key - 'C' (column), Cipher char - 'E'
  • Second char from plain text - 'A' (row), second char from key - 'S' (column), Cipher char - 'S'
  • Third char from plain text - 'L' (row), third char from key - 'E' (column), Cipher char - 'P'
  • Fourth char from plain text - 'I' (row), fourth char from key - 'C' (column), Cipher char - 'K'
  • fifth char from plain text - 'F' (row), fifth char from key - 'C' (column), Cipher char - 'H'
  • Sixth char from plain text - 'O' (row), sixth char from key - 'S' (column), Cipher char - 'G'
  • Seventh char from plain text - 'R' (row), seventh char from key - 'E' (column), Cipher char - 'V'
  • Eightieth  char from plain text - 'N' (row), eightieth char from key - 'C' (column), Cipher char - 'P'
  • Ninth char from plain text - 'I' (row), ninth char from key - 'C' (column), Cipher char - 'K'
  • Tenth char from plain text - 'A' (row), tenth char from key - 'S' (column), Cipher char - 'S'
  • Cipher Text will be the combination cipher char at respective postions thus Cipher text is ESPKHGVPKS.

Conclusion

• Answer A) Cipher text : LWVUGQ
• Answer B) Cipher text : ESPKHGVPKS