Signature-Free Zone (SFZ)

A stock MeshCore repeater firmware with one opinion: it does not relay MeshOS "signed channel messages."

Built for laughs in October 2026, after the MeshOS signed-messages feature landed on the UK mesh. It is a joke firmware — a counter-toy. Not affiliated with, endorsed by, or supported by the MeshCore project or the MeshOS project.

What it does

• After a group message is decrypted, the repeater checks for the MeshOS signed-message ending: 0x00 0x53 0x01 <signer key id 8B> <Ed25519 signature 64B> (zero-padded to the AES block boundary).
• If present: the packet is marked do-not-retransmit — this node refuses to carry it onwards — and a line is printed on serial: [SFZ] signed message blocked - this repeater is a signature-free zone. (blocked: N)
• The Public channel is sniffed with the well-known key (hash byte 0x11), so signed messages on Public are always caught — even when the node has no channel keys configured. Any other channel is checked whenever this node can decrypt it.

Build

pio run -e Heltec_v3_repeater_sfz

Every repeater board has an _sfz twin of its stock <Board>_repeater env (91 targets). Build them all with FIRMWARE_VERSION=<ver> sh build.sh build-sfz-firmwares, or run the Build SFZ Firmwares GitHub Actions workflow to build the whole set and attach it to a draft release.

Merged image output lands in .pio/build/<env>/ (via merge-bin.py).

Flash

pio run -e Heltec_v3_repeater_sfz -t upload

or esptool with the merged .bin (write at offset 0x0). Back up your current flash first.

Test

pio test -e native -f test_signature_free_zone

Caveats (it's a joke, but honest)

• Only blocks messages this node can decrypt (Public: always; other channels: only if configured).
• Detection is structural — it does not verify signatures (it couldn't).
• Only affects this node's relaying — the rest of the mesh happily carries signed messages.
• No effect on direct messages, adverts, or anything unsigned.

Full notes: SIGNATURE_FREE_ZONE.md

Upstream

Based on stock MeshCore (tag repeater-v1.17.1 — https://github.com/meshcore-dev/MeshCore), MIT licensed; see license.txt. For MeshCore itself, get it from upstream.