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Vernam Cipher in Cryptography

  • Difficulty Level : Medium
  • Last Updated : 25 Nov, 2020

Vernam Cipher is a method of encrypting alphabetic text. It is one of the Transposition techniques for converting a plain text into a cipher text. In this mechanism we assign a number to each character of the Plain-Text, like (a = 0, b = 1, c = 2, … z = 25). 

Method to take key: 
In Vernam cipher algorithm, we take a key to encrypt the plain text which length should be equal to the length of the plain text. 

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Encryption Algorithm: 

  1. Assign a number to each character of the plain-text and the key according to alphabetical order. 
  2. Add both the number (Corresponding plain-text character number and Key character number). 
  3. Subtract the number from 26 if the added number is greater than 26, if it isn’t then leave it. 



Now according to our encryption algorithm we assign a number to each character of our plain-text and key. 


PT:   R  A  M   S   W   A  R   U   P   K
NO:   17 0  12  18  22  0  17  20  15  10

KEY:  R   A  N   C  H  O   B  A  B  A  
NO:   17  0  13  2  7  14  1  0  1  0 

Now add the number of Plain-Text and Key and after doing the addition and subtraction operation (if required), we will get the corresponding Cipher-Text character number. 

CT-NO: 34  0  25  20  29  14  18  20  16  10 

In this case, there are two numbers which are greater than the 26 so we have to subtract 26 from them and after applying the subtraction operation the new Cipher text character numbers are as follow: 


CT-NO:  8  0  25   20   3   14   18   20   16   10 

New Cipher-Text is after getting the corresponding character from the number. 


CIPHER-TEXT: I  A  Z  U  D  O  S  U  Q  K 

For the Decryption apply the just reverse process of encryption.

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