C++ Program to perform message encoding using matrix multiplication

This C program uses matrix multiplication to encode a message. This type of coding uses a big matrix to encrypt a message, and it is very hard to break. The message's recipient decodes it by using the matrix's inverse. The encoding matrix is the first matrix, and the decoding matrix is its inverse.

It is the C program's source code for encoding and decoding messages using the matrix multiplication method. On a Linux system, the C program compiles and runs successfully. Shown below is the program output as well.

Program:

#include <stdio.h>
#include <string.h>

void mul(int key[3][3], int message[3][10], int result[3][10])
{
 int c, d, sum, k;
 for (c = 0; c < 3; c++)
 {
 for (d = 0; d < 10; d++)
 {
 sum = 0;
 for (k = 0; k < 3; k++)
 {
 sum = sum + key[c][k] * message[k][d];
 }
 result[c][d] = sum;
 }
 }
}

int main()
{
 char str[30] = "example program to demonstrate";
 int len;
 int i, j;
 int result[3][10] = {0};
 int key[3][3] = {
 {1, 2, 3},
 {0, -1, 1},
 {-1, 1, 2}
 };
 int decode_key[3][3] = {
 {4, 5, 6},
 {7, 8, 9},
 {10, 11, 12}
 };
 int encode[3][10] = {32};
 int decode[3][10] = {0};
 len = strlen(str);

 for (i = 0; i < 10; i++)
 {
 for (j = 0; j < 3; j++)
 {
 if (str[j + i * 3] >= 'a' && str[j + i * 3] <= 'z')
 {
 encode[j][i] = str[j + i * 3] - 96;
 }
 if (str[j + i * 3] == 32)
 {
 encode[j][i] = 32;
 }
 if (str[j + i * 3] == '\0')
 break;
 }
 if (str[j + i * 3] == '\0')
 break;
 }

 mul(key, encode, result);
 printf("Encoded message to be sent: ");
 for (i = 0; i < 10; i++)
 {
 for (j = 0; j < 3; j++)
 printf("%d, ", result[j][i]);
 }

 printf("\nDecoded message is: ");
 mul(decode_key, result, decode);
 for (i = 0; i < 10; i++)
 {
 for (j = 0; j < 3; j++)
 {
 if ((decode[j][i] + 96) >= 97 && (decode[j][i] + 96) <= 123)
 printf("%c", (decode[j][i] + 96));
 else if (decode[j][i] == 32)
 printf(" ");
 }
 }

 return 0;
}

Output:

Encoded message to be sent: 15, 22, 37, 17, 29, 50, 18, 24, 39, 23, 
Decoded message is: example program to demonstrate

Explanation:

This program multiplies the message by matrix using a key matrix, and then uses a separate decode key matrix to decode the message.

Use the key matrix (key) and decode key matrix (decode_key) to encode and decode a message. The program encodes the message, and then the encoded data is outputted as integers. After that, the message is decoded using the decode key matrix, and the resultant decoded message is printed.

For encoding and decoding, the program translates lowercase characters to equivalent values between 1 and 26, assuming that the input text is all lowercase and devoid of special characters.

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