Implement Hill Cipher encryption and decryption in C.

 Hill Cipher encryption and decryption in C.

#include<stdio.h>

#include<math.h>

float encrypt[3][1], decrypt[3][1], a[3][3], b[3][3], mes[3][1], s[3][3];

void encryption(); //encrypts the message

void decryption(); //decrypts the message

void getKeyMessage(); //gets key and message from user

void inverse(); //finds inverse of key matrix

void main() {

getKeyMessage();

encryption();

decryption();

}

void encryption() {

int i, j, k;

for(i = 0; i < 3; i++)

for(j = 0; j < 1; j++)

for(k = 0; k < 3; k++)

encrypt[i][j] = encrypt[i][j] + a[i][k] * mes[k][j];

printf("\nEncrypted string is: ");

for(i = 0; i < 3; i++)

printf("%c", (char)( fmod(encrypt[i][0], 26) + 97));

}

void decryption() {

int i, j, k;

inverse();

for(i = 0; i < 3; i++)

for(j = 0; j < 1; j++)

for(k = 0; k < 3; k++)

decrypt[i][j] = decrypt[i][j] + b[i][k] * encrypt[k][j];

printf("\nDecrypted string is: ");

for(i = 0; i < 3; i++)

printf("%c", (char)(fmod(decrypt[i][0], 26) + 97));

printf("\n");

}

void getKeyMessage() {

int i, j;

char msg[3];

printf("Enter 3x3 matrix for key (It should be inversible):\n");

for(i = 0; i < 3; i++)

for(j = 0; j < 3; j++) {

scanf("%f", &a[i][j]);

c[i][j] = a[i][j];

}

printf("\nEnter a 3 letter string: ");

scanf("%s", msg);

for(i = 0; i < 3; i++)

mes[i][0] = msg[i] - 97;

}

void inverse() {

int i, j, k;

float p, q;

for(i = 0; i < 3; i++)

for(j = 0; j < 3; j++) {

if(i == j)

b[i][j]=1;

else

b[i][j]=0;

}

for(k = 0; k < 3; k++) {

for(i = 0; i < 3; i++) {

p = s[i][k];

q = s[k][k];

for(j = 0; j < 3; j++) {

if(i != k) {

s[i][j] = s[i][j]*q - p*s[k][j];

b[i][j] = b[i][j]*q - p*b[k][j];

}

}

}

}

for(i = 0; i < 3; i++)

for(j = 0; j < 3; j++)

b[i][j] = b[i][j] / s[i][i];

printf("\n\nInverse Matrix is:\n");

for(i = 0; i < 3; i++) {

for(j = 0; j < 3; j++)

printf("%d ", b[i][j]);

printf("\n");

}

}

OUTPUT

Hill Cipher