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Use hardware RNG for session passkey and PKC extra nonce (#11047)

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* Use hardware RNG for session passkey and PKC extra nonce

The admin session passkey and the Curve25519 extra nonce were drawn
from Arduino random(), which is not a CSPRNG. Source them from
HardwareRNG::fill, mirroring the signing path, and fall back to the
seeded CSPRNG (CryptRNG) only when no hardware source is available.

* AdminModule: make session passkey expiry rollover-safe

session_time was compared as millis()/1000 seconds with additive
thresholds, which breaks across the millis() wrap and could keep a stale
admin session key valid. Store session_time in millis() and use
Throttle::isWithinTimespanMs for the 150s refresh and 300s validity
windows.

* AdminModule: track session passkey validity with an explicit flag

session_time == 0 was used as the uninitialized sentinel, but millis()
is legitimately 0 in the first millisecond of uptime, so a passkey
issued then would be treated as no session. Use a dedicated
session_passkey_valid flag instead.

* AdminModule: camelCase the session passkey validity flag

---------

Co-authored-by: Ben Meadors <benmmeadors@gmail.com>
This commit is contained in:
Thomas Göttgens
2026-07-17 15:49:00 -05:00
committed by GitHub
co-authored by Ben Meadors
parent ac027ec5ca
commit d4aa7760cc
3 changed files with 22 additions and 8 deletions
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src/mesh/CryptoEngine.cpp
+5 -1
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@@ -224,7 +224,11 @@ bool CryptoEngine::encryptCurve25519(uint32_t toNode, uint32_t fromNode, meshtas
uint64_t packetNum, size_t numBytes, const uint8_t *bytes, uint8_t *bytesOut)
{
uint8_t *auth;
long extraNonceTmp = random();
// The extra nonce must be unpredictable: use the hardware RNG, falling back to the
// seeded CSPRNG only when no hardware source is available.
uint32_t extraNonceTmp;
if (!HardwareRNG::fill((uint8_t *)&extraNonceTmp, sizeof(extraNonceTmp)))
CryptRNG.rand((uint8_t *)&extraNonceTmp, sizeof(extraNonceTmp));
auth = bytesOut + numBytes;
memcpy((uint8_t *)(auth + 8), &extraNonceTmp,
sizeof(uint32_t)); // do not use dereference on potential non aligned pointers : *extraNonce = extraNonceTmp;