Playfair cipher
#include <stdio.h>
#include <string.h>
#include <ctype.h>
#define MX 5
int choice;
void playfair(char chr1, char chr2, char key[MX][MX]) {
int i, j, s, x1, y1, z1;
for (i = 0; i < MX; i++) {
for (j = 0; j < MX; j++) {
if (chr1 == key[i][j]) {
s = i;
x1 = j;
} else if (chr2 == key[i][j]) {
y1 = i;
z1 = j;
}
}
}
//printf("%d%d %d%d",w,x,y,z);
if (s == y1) {
if(choice==1){
x1 = (x1 + 1) % 5;
z1 = (z1 + 1) % 5;
}
else{
x1 = ((x1 - 1) % 5+5)%5;
z1 = ((z1 - 1) % 5+5)%5;
}
printf("%c%c", key[s][x1], key[y1][z1]);
} else if (x1 == z1) {
if(choice==1){
s = (s + 1) % 5;
y1 = (y1 + 1) % 5;
}
else{
s = ((s - 1) % 5+5)%5;
y1 = ((y1 - 1) % 5+5)%5;
}
printf("%c%c", key[s][x1], key[y1][z1]);
}
else {
printf("%c%c", key[s][z1], key[y1][x1]);
}
}
void removeDuplicates(char str[]){
int hash[256] = {0};
int currentIndex = 0;
int lastUniqueIndex = 0;
while(*(str+currentIndex)){
char temp = *(str+currentIndex);
if(0 == hash[temp]){
hash[temp] = 1;
*(str+lastUniqueIndex) = temp;
lastUniqueIndex++;
}
currentIndex++;
}
*(str+lastUniqueIndex) = '\0';
}
void main() {
int i, j, k = 0, l1, m = 0, n1;
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("\n1.Encryption\n2.Decryption\n\nChoice(1 or 2):");
scanf("%d",&choice);
if(choice!=1 && choice!=2){ printf("Invalid Choice"); return;}
fflush(stdin);
printf("\nEnter key:");
gets(keystr);
printf("Enter the text:");
gets(str);
removeDuplicates(keystr);
n1 = strlen(keystr);
//convert the characters to uppertext
for (i = 0; i < n1; 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 < n1; k++) {
if (keystr[k] == alpa[i]) break;
else if (alpa[i] == 'J') break;
}
if (k == n1) {
keyminus[j] = alpa[i];
j++;
}
}
//construct key keymatrix
k = 0;
for (i = 0; i < MX; i++) {
for (j = 0; j < MX; j++) {
if (k < n1) {
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("\nEntered text :%s\nOutput 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++;
}
}
}
if(choice==2) printf(" (Remove unnecessary X)");
}
OUTPUT
Encryption
1.Encryption
2.Decryption
Choice(1 or 2):1
Enter key:Enter the text:computer
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
Entered text :COMPUTER
Output Text :EMKRYPCT
Decryption
1.Encryption
2.Decryption
Choice(1 or 2):2
Enter key:Enter the text:computer
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
Entered text :COMPUTER
Output Text :EMKRYPCT
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| Playfair cipher |
