ESP-NOW

A sender registers peers by MAC address and transmits; there is no connection setup, which keeps latency and power use low. Frames can go to one peer or be broadcast to all in range.

Unicast frames can be encrypted with CCMP, using a primary key and a local key per peer. ESP-IDF allows 20 paired peers in total, and only some of them encrypted: 7 by default, configurable up to 17 on most chips.

ESP-NOW is a common choice for sensors, remotes, and small control networks built on Espressif parts, because it needs no router and a device can wake, send, and sleep quickly.

Its scope is narrow: it is specific to Espressif, carries small frames, limits encrypted peers, and sends only between radios in range, with no routing across hops. Larger or multi-hop networks are built on top, for example with ESP-WIFI-MESH or an application protocol.

Offline Protocol's embedded leaf is a no_std Rust build of the protocol that sits above whatever link layer a device already has and joins an MLS (RFC 9420) group as a member, so a device's messages are end-to-end encrypted and authenticated, not only protected on one link.

Since SDK v0.28.0 the leaf compiles, gated in CI, for the RISC-V ESP32 parts (ESP32-C6, ESP32-H2, ESP32-C3, ESP32-C2) beside Cortex-M targets. That is a compile result for firmware teams to build on, not a qualified target: nothing has been linked into an ESP32 firmware image or run on a board, the Xtensa chips such as the original ESP32 and ESP32-S3 have not been tried, and the firmware supplies the radio, storage, entropy, and clock. ESP-NOW and the leaf work at different layers: one moves frames between nearby radios, the other encrypts and authenticates the messages inside them. See Zigbee for another low-power option.