Crypto: rweather and ed25519

ED25519 · SHA256 · AES · TWO IMPLEMENTATIONS

MeshCore carries two Ed25519 implementations in the build. One comes from rweather/Crypto, the other is vendored into lib/ed25519. Both are used, in the same file, for different operations — and the reason for that is written in the source as a comment.

[!NOTE] Source. This page was verified against the firmware itself: MeshCore v1.16.0, commit 03b6ef4, 28 July 2026 — files platformio.ini, src/Identity.cpp, src/Packet.cpp, src/Utils.cpp, src/helpers/RegionMap.cpp, src/helpers/TransportKeyStore.cpp, lib/ed25519/ and test/mocks/.

[!NOTE] This chapter is about which library supplies which function and why there are two. How MeshCore's encryption works is described in ../../technical/key-encryption.md.

What it does

rweather/Crypto by Rhys Weatherley is a collection of cryptographic algorithms for Arduino: AES in several key lengths and modes, the SHA family, ChaCha, Poly1305, Curve25519 and Ed25519. The algorithms are optimised for 8-bit microcontrollers and work with a fixed, statically allocated state. Documentation and background live at rweather/arduinolibs.

lib/ed25519 is something else: a compact C implementation of Ed25519 only, present as source inside the MeshCore repo. PlatformIO compiles everything in lib/ automatically, so that code enters every build without a lib_deps line.

How MeshCore pulls it in

platformio.ini r.23

  rweather/Crypto @ ^0.4.0

The line sits in [arduino_base] and therefore applies to all 507 build targets. lib/ed25519 has no line: that directory is picked up automatically.

How MeshCore uses it

src/Identity.cpp opens with both implementations side by side:

src/Identity.cpp r.3-5

#define ED25519_NO_SEED  1
#include <ed_25519.h>
#include <Ed25519.h>

ed_25519.h is the vendored version, Ed25519.h the one from rweather/Crypto. When verifying a signature, the first is deliberately skipped:

src/Identity.cpp r.17-23

bool Identity::verify(const uint8_t* sig, const uint8_t* message, int msg_len) const {
#if 0
  // NOTE:  memory corruption bug was found in this function!!
  return ed25519_verify(sig, message, msg_len, pub_key);
#else
  return Ed25519::verify(sig, this->pub_key, message, msg_len);
#endif
}

So verification goes through rweather/Crypto. Every other Ed25519 operation does go through the vendored version: creating a key pair (r.48), deriving a public key from a private one (r.53 and r.131), signing (r.136) and the key exchange (r.79-82 and r.140).

src/Identity.cpp r.135-141

void LocalIdentity::sign(uint8_t* sig, const uint8_t* message, int msg_len) const {
  ed25519_sign(sig, message, msg_len, pub_key, prv_key);
}

void LocalIdentity::calcSharedSecret(uint8_t* secret, const uint8_t* other_pub_key) const {
  ed25519_key_exchange(secret, other_pub_key, prv_key);
}

Outside Identity.cpp, rweather/Crypto supplies two other algorithms. SHA256 is included in src/Packet.cpp r.3, src/helpers/RegionMap.cpp r.3 and src/helpers/TransportKeyStore.cpp r.2; AES and SHA256 together in src/Utils.cpp:

src/Utils.cpp r.1-3

#include "Utils.h"
#include <AES.h>
#include <SHA256.h>

For the test build the library is replaced. test/mocks/ holds its own AES.h and SHA256.h; [env:native] puts that directory on the include path (platformio.ini r.162) so the tests run without the real implementation.

What it means for a node

Every node carries both implementations. That takes up flash space, and it means that a signature this node produces is made with different code from the code it checks an incoming signature with. Both follow the same standard, so that works — but anyone reading MeshCore's crypto code has to know that Ed25519:: and ed25519_ are different libraries.

The note next to verify is not historical noise: the comment states that memory corruption was found in ed25519_verify. That function has been behind #if 0 ever since.

Sources

• platformio.ini
• src/Identity.cpp
• src/Utils.cpp
• src/Packet.cpp
• src/helpers/TransportKeyStore.cpp
• lib/ed25519/
• test/mocks/
• rweather/arduinolibs

Translated from Dutch by Anthropic Claude