Reduce key duplication by enabling hardware RNG (#8803)

* Reduce key duplication by enabling hardware RNG

* Apply suggestion from @Copilot

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Apply suggestion from @Copilot

Use micros() for worst case random seed for nrf52

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

* Minor cleanup, remove dead code and clarify comment

* trunk

* Add useRadioEntropy bool, default false.

---------

Co-authored-by: Ben Meadors <benmmeadors@gmail.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Jonathan Bennett <jbennett@incomsystems.biz>

src/mesh/CryptoEngine.cpp

@@ -4,6 +4,7 @@
 #include <memory>
 
 #if !(MESHTASTIC_EXCLUDE_PKI)
+#include "HardwareRNG.h"
 #include "NodeDB.h"
 #include "aes-ccm.h"
 #include "meshUtils.h"
@@ -26,6 +27,15 @@ void CryptoEngine::generateKeyPair(uint8_t *pubKey, uint8_t *privKey)
 {
     // Mix in any randomness we can, to make key generation stronger.
     CryptRNG.begin(optstr(APP_VERSION));
+
+    uint8_t hardwareEntropy[64] = {0};
+    if (HardwareRNG::fill(hardwareEntropy, sizeof(hardwareEntropy), true)) {
+        CryptRNG.stir(hardwareEntropy, sizeof(hardwareEntropy));
+    } else {
+        LOG_WARN("Hardware entropy unavailable, falling back to software RNG");
+    }
+    memset(hardwareEntropy, 0, sizeof(hardwareEntropy));
+
     if (myNodeInfo.device_id.size == 16) {
         CryptRNG.stir(myNodeInfo.device_id.bytes, myNodeInfo.device_id.size);
     }

src/mesh/HardwareRNG.cpp

@@ -0,0 +1,159 @@
+#include "HardwareRNG.h"
+
+#include <algorithm>
+#include <cstring>
+#include <random>
+
+#include "configuration.h"
+
+#if HAS_RADIO
+#include "RadioLibInterface.h"
+#endif
+
+#if defined(ARCH_NRF52)
+#include <Adafruit_nRFCrypto.h>
+extern Adafruit_nRFCrypto nRFCrypto;
+#elif defined(ARCH_ESP32)
+#include <esp_system.h>
+#elif defined(ARCH_RP2040)
+#include <Arduino.h>
+#elif defined(ARCH_PORTDUINO)
+#include <random>
+#include <sys/random.h>
+#include <unistd.h>
+#endif
+
+namespace HardwareRNG
+{
+
+namespace
+{
+void fillWithRandomDevice(uint8_t *buffer, size_t length)
+{
+    std::random_device rd;
+    size_t offset = 0;
+    while (offset < length) {
+        uint32_t value = rd();
+        size_t toCopy = std::min(length - offset, sizeof(value));
+        memcpy(buffer + offset, &value, toCopy);
+        offset += toCopy;
+    }
+}
+
+#if HAS_RADIO
+bool mixWithLoRaEntropy(uint8_t *buffer, size_t length)
+{
+    // Only attempt to pull entropy from the modem if it is initialized and exposes the helper.
+    // When the radio stack is disabled or has not yet been configured, we simply skip this step
+    // and return false so callers know no extra mixing occurred.
+    RadioLibInterface *radio = RadioLibInterface::instance;
+    if (!radio) {
+        LOG_ERROR("No radio instance available to provide entropy");
+        return false;
+    }
+
+    constexpr size_t chunkSize = 16;
+    uint8_t scratch[chunkSize];
+    size_t offset = 0;
+    bool mixed = false;
+
+    while (offset < length) {
+        size_t toCopy = std::min(length - offset, chunkSize);
+
+        // randomBytes() returns false if the modem does not support it or is not ready
+        // (for instance, when the radio is powered down). We break immediately to avoid
+        // blocking or returning partially-filled entropy and simply report failure.
+        if (!radio->randomBytes(scratch, toCopy)) {
+            break;
+        }
+
+        for (size_t i = 0; i < toCopy; ++i) {
+            buffer[offset + i] ^= scratch[i];
+        }
+
+        mixed = true;
+        offset += toCopy;
+    }
+
+    // Avoid leaving the modem-sourced bytes sitting on the stack longer than needed.
+    if (mixed) {
+        memset(scratch, 0, sizeof(scratch));
+    }
+
+    return mixed;
+}
+#endif
+} // namespace
+
+bool fill(uint8_t *buffer, size_t length, bool useRadioEntropy)
+{
+    if (!buffer || length == 0) {
+        return false;
+    }
+
+    bool filled = false;
+
+#if defined(ARCH_NRF52)
+    // The Nordic SDK RNG provides cryptographic-quality randomness backed by hardware.
+    nRFCrypto.begin();
+    auto result = nRFCrypto.Random.generate(buffer, length);
+    nRFCrypto.end();
+    filled = result;
+#elif defined(ARCH_ESP32)
+    // ESP32 exposes a true RNG via esp_fill_random().
+    esp_fill_random(buffer, length);
+    filled = true;
+#elif defined(ARCH_RP2040)
+    // RP2040 has a hardware random number generator accessible through the Arduino core.
+    size_t offset = 0;
+    while (offset < length) {
+        uint32_t value = rp2040.hwrand32();
+        size_t toCopy = std::min(length - offset, sizeof(value));
+        memcpy(buffer + offset, &value, toCopy);
+        offset += toCopy;
+    }
+    filled = true;
+#elif defined(ARCH_PORTDUINO)
+    // Prefer the host OS RNG first when running under Portduino.
+    ssize_t generated = ::getrandom(buffer, length, 0);
+    if (generated == static_cast<ssize_t>(length)) {
+        filled = true;
+    }
+
+    if (!filled) {
+        fillWithRandomDevice(buffer, length);
+        filled = true;
+    }
+#endif
+
+    if (!filled) {
+        // As a last resort, fall back to std::random_device. This should only be reached
+        // if a platform-specific source was unavailable.
+        fillWithRandomDevice(buffer, length);
+        filled = true;
+    }
+
+#if HAS_RADIO
+    if (useRadioEntropy) {
+        // Best-effort: if the radio is active and can provide modem entropy, XOR it over the
+        // buffer to improve overall quality. We consider the filling a success if either a
+        // good platform RNG or the modem RNG provided data, so we return true as long as at
+        // least one of those steps succeeded.
+        filled = mixWithLoRaEntropy(buffer, length) || filled;
+    }
+#endif
+
+    return filled;
+}
+
+bool seed(uint32_t &seedOut)
+{
+    uint32_t candidate = 0;
+    if (!fill(reinterpret_cast<uint8_t *>(&candidate), sizeof(candidate), true)) {
+        return false;
+    }
+    seedOut = candidate;
+    return true;
+}
+
+} // namespace HardwareRNG

src/mesh/HardwareRNG.h

@@ -0,0 +1,28 @@
+#pragma once
+
+#include <cstddef>
+#include <cstdint>
+
+namespace HardwareRNG
+{
+
+/**
+ * Fill the provided buffer with random bytes sourced from the most
+ * appropriate hardware-backed RNG available on the current platform.
+ *
+ * @param buffer Destination buffer for random bytes
+ * @param length Number of bytes to write
+ * @param useRadioEntropy If true, attempt to mix radio entropy into the output as well.
+ * @return true if the buffer was fully populated with entropy, false on failure
+ */
+bool fill(uint8_t *buffer, size_t length, bool useRadioEntropy = false);
+
+/**
+ * Populate a 32-bit seed value with hardware-backed randomness where possible.
+ *
+ * @param seedOut Destination for the generated seed value
+ * @return true if a seed was produced from a reliable entropy source
+ */
+bool seed(uint32_t &seedOut);
+
+} // namespace HardwareRNG

src/mesh/RadioLibInterface.cpp

@@ -246,6 +246,24 @@ bool RadioLibInterface::findInTxQueue(NodeNum from, PacketId id)
     return txQueue.find(from, id);
 }
 
+bool RadioLibInterface::randomBytes(uint8_t *buffer, size_t length)
+{
+    if (!buffer || length == 0 || !iface) {
+        return false;
+    }
+
+    // Older RadioLib versions only expose random(min, max), so fill the buffer byte-by-byte.
+    for (size_t i = 0; i < length; ++i) {
+        int32_t value = iface->random(0, 255);
+        if (value < 0) {
+            return false;
+        }
+        buffer[i] = static_cast<uint8_t>(value & 0xFF);
+    }
+
+    return true;
+}
+
 /** radio helper thread callback.
 We never immediately transmit after any operation (either Rx or Tx). Instead we should wait a random multiple of
 'slotTimes' (see definition in RadioInterface.h) taken from a contention window (CW) to lower the chance of collision.
@@ -587,4 +605,4 @@ bool RadioLibInterface::startSend(meshtastic_MeshPacket *txp)
 
         return res == RADIOLIB_ERR_NONE;
     }
-}
+}

src/mesh/RadioLibInterface.h

@@ -172,6 +172,12 @@ class RadioLibInterface : public RadioInterface, protected concurrency::Notified
     /** Attempt to find a packet in the TxQueue. Returns true if the packet was found. */
     virtual bool findInTxQueue(NodeNum from, PacketId id) override;
 
+    /**
+     * Request randomness sourced from the LoRa modem, if supported by the active RadioLib interface.
+     * @return true if len bytes were produced, false otherwise.
+     */
+    bool randomBytes(uint8_t *buffer, size_t length);
+
   private:
     /** if we have something waiting to send, start a short (random) timer so we can come check for collision before actually
      * doing the transmit */

src/platform/nrf52/main-nrf52.cpp

@@ -17,6 +17,7 @@
 #include <nrfx_wdt.h>
 #include <stdio.h>
 // #include <Adafruit_USBD_Device.h>
+#include "HardwareRNG.h"
 #include "NodeDB.h"
 #include "PowerMon.h"
 #include "error.h"
@@ -398,15 +399,14 @@ void nrf52Setup()
 #endif
 
     // Init random seed
-    union seedParts {
-        uint32_t seed32;
-        uint8_t seed8[4];
-    } seed;
-    nRFCrypto.begin();
-    nRFCrypto.Random.generate(seed.seed8, sizeof(seed.seed8));
-    LOG_DEBUG("Set random seed %u", seed.seed32);
-    randomSeed(seed.seed32);
-    nRFCrypto.end();
+    uint32_t seed = 0;
+    if (!HardwareRNG::seed(seed)) {
+        LOG_WARN("Hardware RNG seed unavailable, using PRNG fallback");
+        // Use a hardware timer value as a fallback seed for better entropy
+        seed = micros();
+    }
+    LOG_DEBUG("Set random seed %u", seed);
+    randomSeed(seed);
 
     // Set up nrfx watchdog. Do not enable the watchdog yet (we do that
     // the first time through the main loop), so that other threads can

src/platform/portduino/PortduinoGlue.cpp

@@ -1,4 +1,5 @@
 #include "CryptoEngine.h"
+#include "HardwareRNG.h"
 #include "PortduinoGPIO.h"
 #include "SPIChip.h"
 #include "mesh/RF95Interface.h"
@@ -233,7 +234,9 @@ void portduinoSetup()
         std::cout << "Running in simulated mode." << std::endl;
         portduino_config.MaxNodes = 200; // Default to 200 nodes
         // Set the random seed equal to TCPPort to have a different seed per instance
-        randomSeed(TCPPort);
+        uint32_t seed = TCPPort;
+        HardwareRNG::seed(seed);
+        randomSeed(seed);
         return;
     }
 
@@ -512,7 +515,9 @@ void portduinoSetup()
 #endif
     printf("MAC ADDRESS: %02X:%02X:%02X:%02X:%02X:%02X\n", dmac[0], dmac[1], dmac[2], dmac[3], dmac[4], dmac[5]);
     // Rather important to set this, if not running simulated.
-    randomSeed(time(NULL));
+    uint32_t seed = static_cast<uint32_t>(time(NULL));
+    HardwareRNG::seed(seed);
+    randomSeed(seed);
 
     std::string defaultGpioChipName = gpioChipName + std::to_string(portduino_config.lora_default_gpiochip);
 

src/platform/rp2xx0/main-rp2xx0.cpp

@@ -1,3 +1,4 @@
+#include "HardwareRNG.h"
 #include "configuration.h"
 #include "hardware/xosc.h"
 #include <hardware/clocks.h>
@@ -98,10 +99,12 @@ void getMacAddr(uint8_t *dmac)
 
 void rp2040Setup()
 {
-    /* Sets a random seed to make sure we get different random numbers on each boot.
-       Taken from CPU cycle counter and ROSC oscillator, so should be pretty random.
-    */
-    randomSeed(rp2040.hwrand32());
+    /* Sets a random seed to make sure we get different random numbers on each boot. */
+    uint32_t seed = 0;
+    if (!HardwareRNG::seed(seed)) {
+        seed = rp2040.hwrand32();
+    }
+    randomSeed(seed);
 
 #ifdef RP2040_SLOW_CLOCK
     uint f_pll_sys = frequency_count_khz(CLOCKS_FC0_SRC_VALUE_PLL_SYS_CLKSRC_PRIMARY);