F439_CPP_TX-RX_LoRa_Project

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Replay Protection Mechanism

This page describes how the RadioLink protocol prevents replay attacks.

## Design Overview

RadioLink uses a combination of an epoch value and a monotonic counter to ensure that previously transmitted frames cannot be accepted again by a receiver.

The system follows an epoch‑per‑boot model.

TX node behavior:

- A new epoch is generated on boot
- The epoch is persisted once to FRAM
- A counter increases for every transmitted frame

RX node behavior:

- Tracks the last seen counter for each node
- Rejects frames with stale counter values

## Replay Protection Flow

## Security Properties

The replay protection mechanism provides:

- monotonic frame ordering
- detection of stale frames
- minimal persistent storage writes

Because the epoch is written only once per boot, FRAM wear is minimized while still providing replay protection across power cycles.

## Relationship to RX Pipeline

Replay freshness is enforced during the RX processing pipeline by the stage:

    radioLinkRxReplayIsFresh()

This stage verifies that the received counter is newer than the last accepted value for the sending node.