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Sunday, February 5, 2017

Playfair Encryption

Playfair Encryption implementation 

Playfair is one of the popular cryptographic software security algorithms. This technique encrypts pairs of letters at a time and generates more secure encrypted text compare to  the simple substitution cipher like Caesar.

Assumptions:
  • Assume key matrix is given to us. 
  • Read plain text(2 characters) from user.
  • This program demonstrate four rules of the Playfair encryption algorithm.
  • This program will process only 2 characters input. 
  • You may extend to process n characters by repeating given logic.
  • Add suitable exception for completing this program.

#include<stdio.h>
int main(){
 
  char arr[5][5]={"MONAR","CHYBD","EFGIK","LPQST","UVWXZ"};
  char pt[10];
 
  int i, j, r1=0, r2=0, c1=0, c2=0;
  printf("Playfair Keymatrix\n==================\n");
  for(i=0; i<5; i++)
  {
    for(j=0; j<5; j++)
    printf("%c ", arr[i][j]);
    printf("\n");
  }
 
  printf("Enter your plain text:");
  scanf("%s",pt);
  printf("Your plain text = %s", pt);
 
  for(i=0; i<5; i++)
  {
    for(j=0; j<5; j++)
    {
       if(arr[i][j] == pt[0])
       {
         r1=i; c1=j;
       }
       if(arr[i][j] == pt[1])
       {
         r2=i; c2=j;
       }
    }
  }
  if(r1==r2) //when both characters in same row
  {
    if(c2==4) //for char in last column
       printf("Ciphertext = %c%c \n", arr[r1][c1+1], arr[r2][0]);  
    else
       printf("Ciphertext = %c%c \n", arr[r1][c1+1], arr[r2][c2+1]);
  }
  if(c1==c2)//when both characters in same column
  {
    if(r2==4) //for char in last row
       printf("Ciphertext = %c%c \n", arr[r1+1][c1], arr[0][c2]);
    else
       printf("Ciphertext = %c%c \n", arr[r1+1][c1], arr[r2+1][c2]);
  }
  //when characters are not in a same row and column
  if(r1 != r2 && c1 != c2)
  {
    printf("\nCiphertext = %c%c \n", arr[r1][c2], arr[r2][c1]);
  }
  return 0;
}

Output of the program

Playfair Keymatrix
==================
M O N A R
C H Y B D
E F G I K
L P Q S T
U V W X Z
Enter your plain text:IN
Your plain text = IN
Ciphertext = GA


>>> Playfair Decryption Program


9 comments:

  1. very good programs, written with easy concepts.

    ReplyDelete
    Replies
    1. Thanks Raj Kumar for appreciation...Do follow this blog for latest updates.

      Delete
  2. our sir suggested to view ur website
    it's very easy it understand
    thanq

    ReplyDelete
  3. only valid for 2 lettered string

    ReplyDelete
    Replies
    1. The program logic can be extended using for or while loop for processing more data.

      Delete
  4. Replies
    1. Dear Hardik,
      Share complete details about your error.
      This code works fine on Windows 7 machine with DevC++ editor.

      Delete
  5. string for array of chars is too long [-fpermissive]

    ReplyDelete