#include // Matrices and their inverse counterparts are involved in encryption and decryption of messages, but how? void crypt(std::string str) { int colsize = (str.size() / 3) + (str.size() % 3 != 0); int encryption[3][3] = {{1, 2, 1}, { 2, 5, 3}, { 2, 3, 2}}; int decryption[3][3] = {{1, -1, 1}, { 2, 0, -1}, {-4, 1, 1}}; int ori_matrix[3][colsize]; int res_matrix[3][colsize]; int row, col; // preparing empty arrays (matrices) to store message int values for (int i = 0; i < 3; i++) for (int j = 0; j < colsize; ori_matrix[i][j] = res_matrix[i][j] = 0, j++); // conversion of string to int array (matrix) which represents the original string for (int i = row = col = 0; i < str.size(); i++, row == 2 ? row = 0, col++ : row++) { ori_matrix[row][col] = static_cast(str[i]); } // multiplying the original matrix of the message with the encryption matrix for (int i = row = col = 0; i < 3; i++) for (int j = 0; j < colsize; j++) for (row = col = 0; row < 3 && col < 3; row++, col++) res_matrix[i][j] += encryption[i][col] * ori_matrix[row][j]; // printing the original matrix of the string std::cout << "Untouched matrix...\n\n"; for (int i = 0; i < 3; i++, std::cout << std::endl) for (int j = 0; j < colsize; std::cout << ori_matrix[i][j++] << " "); std::cout << std::endl; // printing the encrypted matrix of the string std::cout << "After encryption...\n\n"; for (int i = 0; i < 3; i++, std::cout << std::endl) for (int j = 0; j < colsize; std::cout << res_matrix[i][j++] << " "); /* Now that we have seen how a message is encrypted through the means of matrix multiplication Let's see if we can revert the encrypted message back to it's original matrix This is achieved by multiplying the encrypted matrix with the inverse of the encryption matrix */ // clearing the original matrix to prepare to store the decrypted matrix for (int i = 0; i < 3; i++) for (int j = 0; j < colsize; ori_matrix[i][j++] = 0); // multiplying the encrypted matrix with with the inverse of the encryption matrix for (int i = row = col = 0; i < 3; i++) for (int j = 0; j < colsize; j++) for (row = col = 0; row < 3 && col < 3; row++, col++) ori_matrix[i][j] += decryption[i][col] * res_matrix[row][j]; std::cout << std::endl; // printing the decrypted matrix std::cout << "After decryption...\n\n"; for (int i = 0; i < 3; i++, std::cout << std::endl) for (int j = 0; j < colsize; std::cout << ori_matrix[i][j++] << " "); } int main() { crypt("This is 3x6 matrix"); return 0; }

Matrix Cryptography