#include<stdio.h>
#include<math.h>
float encrypt[3][1], decrypt[3][1], a[3][3], b[3][3], mes[3][1], c[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
int main() {
getKeyMessage();
encryption();
decryption();
return 0;
}
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 = c[i][k];
q = c[k][k];
for(j = 0; j < 3; j++) {
if(i != k) {
c[i][j] = c[i][j]*q - p*c[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] / c[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");
}
}
