swaits/meshcore-spec

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swaitsandClaude Opus 4.7 9232c16f7c

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feat(versioning): snapshot corpus per spec version

A frozen spec is only meaningful if it's paired with the corpus
that was current at release time — otherwise a v0.1.0 reader
follows "see corpus/payloads/ack/" and lands on a file whose
test vectors may have changed since v0.1.0 was cut.

Three changes:

1. `cut-version` now copies BOTH src/ AND corpus/ into the
   snapshot directory. A release is the pair, not just the text.

2. The corpus URL rewriting in cut-version now retargets
   /tree/main/corpus -> /tree/main/versions/<v>/corpus (and the
   blob variant). This lets the link resolve on GitHub from main
   alone — no git tag required, since the frozen copy is a real
   path under main. Downgrades the "tag is REQUIRED" message from
   last commit back to "optionally tag the commit".

3. The frozen corpus's spec_ref fields get rewritten too: from
   `src/04-payload-ack.md` to `versions/<v>/04-payload-ack.md`,
   so a reader following a test vector lands on the spec text the
   vector was paired with at release time.

versions/v0.1.0/ regenerated from scratch via `just cut-version v0.1.0`
to pick up the corpus snapshot + the new sed patterns. The release
is now self-consistent: v0.1.0 spec links go to v0.1.0 corpus, which
links back to v0.1.0 spec.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

2026-05-12 10:38:02 -06:00

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MeshCore Protocol Specification

Section 7: Payload — Anonymous Request

Overview

The anonymous request payload allows a node to send an encrypted message to a recipient without the recipient needing to know the sender in advance. Instead of a 1-byte source hash, the full 32-byte Ed25519 public key of the sender is included, enabling the recipient to compute the shared secret for decryption.

Payload Type

Header payload type field: 0x07 (ANON_REQ)

Wire Format

 0
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| dest_hash(1)  |                                               |
+-+-+-+-+-+-+-+-+                                               |
|                   Sender Public Key (32 bytes)                |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    Cipher MAC (2 bytes)       |                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+                               |
|              Ciphertext (N × 16 bytes, N ≥ 1)                |
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Fields

Field	Offset	Size	Type	Description
dest_hash	0	1 byte	raw	First byte of recipient's Ed25519 public key
sender_pub_key	1	32 bytes	raw	Full Ed25519 public key of sender
cipher_mac	33	2 bytes	raw	Truncated HMAC-SHA256 over ciphertext
ciphertext	35	variable (multiple of 16)	raw	AES-128-ECB encrypted data

Minimum Size

Minimum payload: 1 + 32 + 2 + 16 = 51 bytes

Encryption

Sender computes ECDH shared secret using its private key and the recipient's public key.
Encrypt plaintext using AES-128-ECB with first 16 bytes of shared secret.
Compute HMAC-SHA256 over ciphertext with full 32-byte shared secret. Truncate to 2 bytes.
Assemble: dest_hash || sender_pub_key || MAC || ciphertext.

Decryption

Read dest_hash. If it does not match this node, the packet is not for us (but MAY be forwarded).
Read 32-byte sender_pub_key. Construct an Identity from it.
Compute ECDH shared secret between this node's private key and sender's public key.
Verify the MAC and decrypt as in Section 14.

Cross-References

Section 6: Encrypted Payloads — Standard encrypted format
Section 14: Cryptography — Encrypt-then-MAC
Section 15: Identity — ECDH key exchange
Test vectors: corpus/payloads/anon-req/

Reference Implementation

Mesh::createAnonDatagram() in src/Mesh.cpp — Encoding
Mesh::onRecvPacket(), case PAYLOAD_TYPE_ANON_REQ — Decoding

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