MeshCore-Solo/variants/sim/SimRNG.h

#pragma once

#include <Utils.h>
#include <cstdlib>
#include <ctime>
#include "SimInstance.h"

// mesh::RNG implementation for the native sim build. Not cryptographically
// strong (rand() under the hood) -- fine for a terminal demo. Phase 3 mixes
// in sim_instance_salt() so that two module instances of the SAME compiled
// binary (the browser's two companion_radio instances) can't end up with
// the same seed -- see SimInstance.h for why that's a real risk here, not
// a hypothetical one. sim_instance_entropy() (also SimInstance.h) mixes in
// real crypto.getRandomValues()-sourced entropy from the host page on top
// of that -- salt alone is a pure function of the tag string ('hero'/'B'/
// 'R'), so it's identical across two genuinely different browser tabs that
// both boot a 'hero' instance; combined with time(NULL)'s 1-second
// resolution and a WASM heap pointer that's fully deterministic (no ASLR
// inside the sandbox) across independent boots, two different real visitors
// landing on the same wall-clock second used to get byte-identical
// generated identities without this.
class SimRNG : public mesh::RNG {
public:
  SimRNG() { }
  void begin() {
    unsigned seed = (unsigned)time(NULL) ^ (unsigned)(uintptr_t)this ^ sim_instance_salt() ^ sim_instance_entropy();
    srand(seed);
  }
  void random(uint8_t* dest, size_t sz) override {
    for (size_t i = 0; i < sz; i++) dest[i] = (uint8_t)rand();
  }
};