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Practicle:-3: AIM:-Implement Playfair Cipher Encryption - Decryption

This document describes implementing the Playfair cipher for encryption and decryption. It includes: 1) Defining a playfair() function that takes two characters and a key matrix to encrypt them. 2) A main() function that gets a key and plaintext from the user, constructs a 5x5 key matrix, and calls playfair() to encrypt pairs of characters and output the cipher text. 3) It handles 'j'/J by replacing with 'i'/I, encrypts single characters with 'X', and maintains the pairs by adding 'X' if odd length plaintext.

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Ridham Vyas
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60 views4 pages

Practicle:-3: AIM:-Implement Playfair Cipher Encryption - Decryption

This document describes implementing the Playfair cipher for encryption and decryption. It includes: 1) Defining a playfair() function that takes two characters and a key matrix to encrypt them. 2) A main() function that gets a key and plaintext from the user, constructs a 5x5 key matrix, and calls playfair() to encrypt pairs of characters and output the cipher text. 3) It handles 'j'/J by replacing with 'i'/I, encrypts single characters with 'X', and maintains the pairs by adding 'X' if odd length plaintext.

Uploaded by

Ridham Vyas
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as RTF, PDF, TXT or read online on Scribd
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Practicle:-3

 AIM:- Implement Playfair cipher encryption-


decryption.
#include<stdio.h>
#include<conio.h>
#include<string.h>
#include<ctype.h>
#define MX 5
int playfair(char ch1,char ch2, char key[MX][MX])
{
int i,j,w,x,y,z;
FILE *out;
if((out=fopen("cipher.txt","a+"))==NULL)
{
printf("File Currupted.");
}

for(i=0;i<MX;i++)
{
for(j=0;j<MX;j++)
{
if(ch1==key[i][j])
{
w=i;
x=j;
}
else if(ch2==key[i][j])
{
y=i;
z=j;
}
}
}
//printf("%d%d %d%d",w,x,y,z);
if(w==y)
{
x=(x+1)%5;z=(z+1)%5;
printf("%c%c",key[w][x],key[y][z]);
fprintf(out, "%c%c",key[w][x],key[y][z]);
}
else if(x==z)
{
w=(w+1)%5;y=(y+1)%5;
printf("%c%c",key[w][x],key[y][z]);
fprintf(out, "%c%c",key[w][x],key[y][z]);
}
else
{

Name:-Ridham Vyas Enrollment No:-170630116035


printf("%c%c",key[w][z],key[y][x]);
fprintf(out, "%c%c",key[w][z],key[y][x]);
}
fclose(out);
}
int main()
{

int i,j,k=0,l,m=0,n;
char key[MX][MX],keyminus[25],keystr[10],str[25]={0};
char
alpa[26]={'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'};

printf("\nEnter key:");
gets(keystr);
printf("\nEnter the plain text:");
gets(str);
n=strlen(keystr);
//convert the characters to uppertext
for (i=0; i<n; i++)
{
if(keystr[i]=='j')keystr[i]='i';
else if(keystr[i]=='J')keystr[i]='I';
keystr[i] = toupper(keystr[i]);

//convert all the characters of plaintext to uppertext


for (i=0; i<strlen(str); i++)
{
if(str[i]=='j')str[i]='i';
else if(str[i]=='J')str[i]='I';
str[i] = toupper(str[i]);

// store all characters except key


j=0;
for(i=0;i<26;i++)
{
for(k=0;k<n;k++)
{
if(keystr[k]==alpa[i])
break;
else if(alpa[i]=='J')
break;
Practicle:-3
}
if(k==n)
{
keyminus[j]=alpa[i];j++;
}
}

//construct key keymatrix


k=0;
for(i=0;i<MX;i++)
{
for(j=0;j<MX;j++)
{
if(k<n)
{
key[i][j]=keystr[k];
k++;}
else
{
key[i][j]=keyminus[m];m++;
}
printf("%c ",key[i][j]);
}
printf("\n");
}

// construct diagram and convert to cipher text


printf("\n\nEntered text :%s\nCipher Text :",str);
for(i=0;i<strlen(str);i++)
{
if(str[i]=='J')str[i]='I';
if(str[i+1]=='\0')
playfair(str[i],'X',key);
else
{
if(str[i+1]=='J')str[i+1]='I';
if(str[i]==str[i+1])
playfair(str[i],'X',key);
else
{
playfair(str[i],str[i+1],key);i++;
}
}
}
getch();
}

Name:-Ridham Vyas Enrollment No:-170630116035


 OUTPUT

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