Designing a quantum‑resistant hash for a tiny MCU is a tightrope walk. You need something that a few kilobytes of flash can hold, runs at a few megahertz, and still throws the quantum computer off its game. First, the classic Merkle–Damgård style hashes (SHA‑256, SHA‑512) can be made quantum‑safe by tweaking the key schedule and the round constants, but the core operation remains susceptible to Grover’s algorithm – you only get a square‑root speed‑up, not a catastrophic blow. For a truly quantum‑safe design you look at *hash‑based* schemes or *lattice‑based* constructions. 1. **Lightweight hash‑based** – SPHINCS+ has a “small” parameter set that can be squeezed into a microcontroller with a few hundred kilobytes of storage. The downside is the signing time and the need to store a tree of signatures. If you only need the hash itself, you can strip it down to the underlying hash chain, but that loses the post‑quantum guarantee. 2. **Lattice‑based** – NTRU or Ring‑Learning‑with‑Errors (RLWE) based hash functions are more efficient in terms of arithmetic, but they still need a moderate word size and a decent amount of memory for the polynomials. You could use a compressed representation and a few modular reductions, but the code tends to be heavier than a pure bit‑wise sponge. 3. **Sponge constructions** – SHA‑3 (Keccak) and BLAKE2s are already light and can be tweaked. If you replace the permutation with a simple, small‑word, linear‑feedback operation that still satisfies the sponge properties, you can get something that runs in a few hundred clock cycles. It won’t be “quantum‑hard” in the same sense as lattice schemes, but for many embedded uses it’s a practical compromise. In short, pick a parameter set that fits your memory budget, use a small‑word, word‑size modular arithmetic for the core, and then layer on a hash‑based or lattice‑based construction if you need true post‑quantum security. The trade‑off is always speed, size, or security – you’ll never get all three at maximum.

Sounds right—just remember the bigger the block you squeeze in, the slower the clock will be. If you can afford the extra kilobytes, the lattice route is the only true quantum‑safe option, but if you’re hunting for minimal latency, a tiny sponge with a 32‑bit tweak will keep the MCU happy, just not the quantum‑attack‑proof ones. Keep the trade‑offs front of mind.

Got it, I'll keep the trade‑offs tight and make sure each design choice is justified.

Makes sense, I'll run the numbers each time to confirm the improvement isn't just theoretical.

Sounds like a good cycle—measure, tweak, repeat. I’ll keep the numbers tight.