Consider any 6x6 matrix (only alphabets) and develop as well as demonstrate an algorithm and code to show the length of the string should be equal to 6
// C program
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define SIZE 30
void toLowerCase(char plain[], int ps)
{
int i;
for (i = 0; i < ps; i++) {
if (plain[i] > 64 && plain[i] < 91)
plain[i] += 32;
}
}
int removeSpaces(char* plain, int ps)
{
int i, count = 0;
for (i = 0; i < ps; i++)
if (plain[i] != ' ')
plain[count++] = plain[i];
plain[count] = '\0';
return count;
}
void generateKeyTable(char key[], int ks, char keyT[5][5])
{
int i, j, k, flag = 0, *dicty;
dicty = (int*)calloc(26, sizeof(int));
for (i = 0; i < ks; i++) {
if (key[i] != 'j')
dicty[key[i] - 97] = 2;
}
dicty['j' - 97] = 1;
i = 0;
j = 0;
for (k = 0; k < ks; k++) {
if (dicty[key[k] - 97] == 2) {
dicty[key[k] - 97] -= 1;
keyT[i][j] = key[k];
j++;
if (j == 5) {
i++;
j = 0;
}
}
}
for (k = 0; k < 26; k++) {
if (dicty[k] == 0) {
keyT[i][j] = (char)(k + 97);
j++;
if (j == 5) {
i++;
j = 0;
}
}
}
}
void search(char keyT[5][5], char a, char b, int arr[])
{
int i, j;
if (a == 'j')
a = 'i';
else if (b == 'j')
b = 'i';
for (i = 0; i < 5; i++) {
for (j = 0; j < 5; j++) {
if (keyT[i][j] == a) {
arr[0] = i;
arr[1] = j;
}
else if (keyT[i][j] == b) {
arr[2] = i;
arr[3] = j;
}
}
}
}
int mod5(int a)
{
return (a % 5);
}
int prepare(char str[], int ptrs)
{
if (ptrs % 2 != 0) {
str[ptrs++] = 'z';
str[ptrs] = '\0';
}
return ptrs;
}
void encrypt(char str[], char keyT[5][5], int ps)
{
int i, a[4];
for (i = 0; i < ps; i += 2) {
search(keyT, str[i], str[i + 1], a);
if (a[0] == a[2]) {
str[i] = keyT[a[0]][mod5(a[1] + 1)];
str[i + 1] = keyT[a[0]][mod5(a[3] + 1)];
}
else if (a[1] == a[3]) {
str[i] = keyT[mod5(a[0] + 1)][a[1]];
str[i + 1] = keyT[mod5(a[2] + 1)][a[1]];
}
else {
str[i] = keyT[a[0]][a[3]];
str[i + 1] = keyT[a[2]][a[1]];
}
}
}
void encryptByPlayfairCipher(char str[], char key[])
{
char ps, ks, keyT[5][5];
ks = strlen(key);
ks = removeSpaces(key, ks);
toLowerCase(key, ks);
ps = strlen(str);
toLowerCase(str, ps);
ps = removeSpaces(str, ps);
ps = prepare(str, ps);
generateKeyTable(key, ks, keyT);
encrypt(str, keyT, ps);
}
// Driver code
int main()
{
char str[SIZE], key[SIZE];
strcpy(key, "Monarchy");
printf("Key text: %s\n", key);
strcpy(str, "instruments");
printf("Plain text: %s\n", str);
encryptByPlayfairCipher(str, key);
printf("Cipher text: %s\n", str);
return 0;
}
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