Persistent Byte Output Counter C++ [closed] - c++

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I am working on a project in which I need to keep track of how many bytes the software dishes out.
The software will be turned on and off occasionally, so I must implement a way to store the number of bytes outputted in a way so that an Administrator or another User cannot simply open the file and change the number of bytes outputted.
What is the best way to implement this?
Also, I am not able to use any libraries (ex: boost).

Answer 1

Here is an example of using https://en.wikipedia.org/wiki/Tiny_Encryption_Algorithm
#include <iostream>
#include <fstream>
void encrypt(uint32_t* v, uint32_t* k) {
uint32_t v0 = v[0], v1 = v[1], sum = 0, i; /* set up */
uint32_t delta = 0x9e3779b9; /* a key schedule constant */
uint32_t k0 = k[0], k1 = k[1], k2 = k[2], k3 = k[3]; /* cache key */
for (i = 0; i < 32; i++) { /* basic cycle start */
sum += delta;
v0 += ((v1 << 4) + k0) ^ (v1 + sum) ^ ((v1 >> 5) + k1);
v1 += ((v0 << 4) + k2) ^ (v0 + sum) ^ ((v0 >> 5) + k3);
} /* end cycle */
v[0] = v0; v[1] = v1;
}
void decrypt(uint32_t* v, uint32_t* k) {
uint32_t v0 = v[0], v1 = v[1], sum = 0xC6EF3720, i; /* set up */
uint32_t delta = 0x9e3779b9; /* a key schedule constant */
uint32_t k0 = k[0], k1 = k[1], k2 = k[2], k3 = k[3]; /* cache key */
for (i = 0; i<32; i++) { /* basic cycle start */
v1 -= ((v0 << 4) + k2) ^ (v0 + sum) ^ ((v0 >> 5) + k3);
v0 -= ((v1 << 4) + k0) ^ (v1 + sum) ^ ((v1 >> 5) + k1);
sum -= delta;
} /* end cycle */
v[0] = v0; v[1] = v1;
}
int main()
{
uint32_t k[4] = { 123,456,789,10 }; // key
uint32_t v[2] = { 1000000, 1000000 }; // data
// save into file
std::ofstream ofs("save.dat", std::ios::binary);
encrypt(v, k);
ofs << v[0] << " " << v[1] << std::endl;
// read from file
std::ifstream ifs("save.dat", std::ios::binary);
uint32_t v2[2];
if (ifs >> v2[0] >> v2[1])
{
std::cout << "Filedata: " << v2[0] << " " << v2[1] << std::endl;
decrypt(v2, k);
if (v2[0] == v2[1])
std::cout << "Decrypted: " << v2[0] << std::endl;
else
std::cout << "Data was tampered with!" << std::endl;
}
}
http://coliru.stacked-crooked.com/view?id=d725bf798ff8ca12
Works pretty good and doesn't need any library. This is low level protection but should be hard enough to discourage your users.