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);
     }