Better random number generation from RSSI

API.md

@@ -331,9 +331,19 @@ LoRa.disableCrc();
 
 ## Other functions
 
+### Get RSSI
+
+Gets the RSSI value from the radio. 
+
+```
+byte b = LoRa.getRSSI();
+```
+
+Returns RSSI value as a byte.
+
 ### Random
 
-Generate a random byte, based on the Wideband RSSI measurement.
+Generate a random byte, based on the Wideband RSSI measurement run through a von Neumann Extractor. **NB** - these are not cryptographically secure random numbers! Use with caution!
 
 ```
 byte b = LoRa.random();

src/LoRa.cpp

@@ -512,9 +512,28 @@ void LoRaClass::disableCrc()
   writeRegister(REG_MODEM_CONFIG_2, readRegister(REG_MODEM_CONFIG_2) & 0xfb);
 }
 
+byte LoRaClass::getRSSI()
+{
+    return readRegister(REG_RSSI_WIDEBAND);
+}
+
 byte LoRaClass::random()
 {
-  return readRegister(REG_RSSI_WIDEBAND);
+  int n=0, bits=7;
+  while(bits--) {
+    n<<=1;
+    while(1){
+      // implement a basic von Neumann Extractor
+      int a=(readRegister(REG_RSSI_WIDEBAND) & 1);
+      if(a != (readRegister(REG_RSSI_WIDEBAND) & 1)){
+        // put random, whitened bit in n
+        n |= a;
+        break;
+      }
+    }
+  }
+  // return the random byte
+  return n;
 }
 
 void LoRaClass::setPins(int ss, int reset, int dio0)

src/LoRa.h

@@ -71,6 +71,7 @@ class LoRaClass : public Stream {
   void crc() { enableCrc(); }
   void noCrc() { disableCrc(); }
 
+  byte getRSSI();
   byte random();
 
   void setPins(int ss = LORA_DEFAULT_SS_PIN, int reset = LORA_DEFAULT_RESET_PIN, int dio0 = LORA_DEFAULT_DIO0_PIN);