Register the noise sources with RNG at setup time

doc/crypto-rng.dox

@@ -103,7 +103,9 @@ TransistorNoiseSource noise(A1);
 \endcode
 
 Then in the setup() function we call \link RNGClass::begin() RNG.begin()\endlink
-to start the random number generator running:
+to start the random number generator running and call
+\link RNGClass::addNoiseSource() RNG.addNoiseSource()\endlink to register
+all of the application's noise sources:
 
 \code
 void setup() {
@@ -111,6 +113,9 @@ void setup() {
     // "MyApp 1.0" and load the previous seed from EEPROM address 500.
     RNG.begin("MyApp 1.0", 500);
 
+    // Add the noise source to the list of sources known to RNG.
+    RNG.addNoiseSource(noise);
+
     // ...
 }
 \endcode
@@ -128,6 +133,7 @@ void setup() {
     RNG.begin("MyApp 1.0", 500);
     RNG.stir(serial_number, sizeof(serial_number));
     RNG.stir(mac_address, sizeof(mac_address));
+    RNG.addNoiseSource(noise);
     ...
 }
 \endcode
@@ -147,18 +153,14 @@ fills up, a save will be automatically forced.
 
 To use the random number generator properly, there are some regular tasks
 that must be performed every time around the application's main loop().
-Newly accumulated noise must be mixed in with
-\link RNGClass::stir() RNG.stir()\endlink and the
-\link RNGClass::loop() RNG.loop()\endlink function must be called to
-perform auto-saves:
+Newly accumulated noise must be mixed in and auto-saves must be performed
+on a regular basis.  The \link RNGClass::loop() RNG.loop()\endlink
+function takes care of these tasks for us:
 
 \code
 void loop() {
     // ...
 
-    // If the noise source has accumulated new entropy, then stir it in.
-    RNG.stir(noise);
-
     // Perform regular housekeeping on the random number generator.
     RNG.loop();
 

libraries/Crypto/RNG.cpp

@@ -70,20 +70,20 @@
  *     // Stir in the Ethernet MAC address.
  *     RNG.stir(mac_address, sizeof(mac_address));
  *
+ *     // Add the noise source to the list of sources known to RNG.
+ *     RNG.addNoiseSource(noise);
+ *
  *     // ...
  * }
  * \endcode
  *
- * The application should regularly call stir() to mix in new data from
- * the noise source and also regularly call loop():
+ * The application should regularly call loop() to stir in new data
+ * from the registered noise sources and to periodically save the seed:
  *
  * \code
  * void loop() {
  *     // ...
  *
- *     // If the noise source has accumulated new entropy, then stir it in.
- *     RNG.stir(noise);
- *
  *     // Perform regular housekeeping on the random number generator.
  *     RNG.loop();
  *
@@ -170,6 +170,7 @@ RNGClass::RNGClass()
     , firstSave(1)
     , timer(0)
     , timeout(3600000UL)    // 1 hour in milliseconds
+    , count(0)
 {
 }
 
@@ -197,7 +198,7 @@ RNGClass::~RNGClass()
  * additional entropy data from noise sources to initialize the random
  * number generator properly.
  *
- * \sa stir(), save()
+ * \sa addNoiseSource(), stir(), save()
  */
 void RNGClass::begin(const char *tag, int eepromAddress)
 {
@@ -234,6 +235,25 @@ void RNGClass::begin(const char *tag, int eepromAddress)
     save();
 }
 
+/**
+ * \brief Adds a noise source to the random number generator.
+ *
+ * \param source The noise source to add, which will be polled regularly
+ * by loop() to accumulate noise-based entropy from the source.
+ *
+ * RNG supports a maximum of four noise sources.  If the application needs
+ * more than that then the application must poll the noise sources itself by
+ * calling NoiseSource::stir() directly.
+ *
+ * \sa loop(), begin()
+ */
+void RNGClass::addNoiseSource(NoiseSource &source)
+{
+    #define MAX_NOISE_SOURCES (sizeof(noiseSources) / sizeof(noiseSources[0]))
+    if (count < MAX_NOISE_SOURCES)
+        noiseSources[count++] = &source;
+}
+
 /**
  * \brief Sets the amount of time between automatic seed saves.
  *
@@ -485,6 +505,10 @@ void RNGClass::save()
  */
 void RNGClass::loop()
 {
+    // Stir in the entropy from all registered noise sources.
+    for (uint8_t posn = 0; posn < count; ++posn)
+        noiseSources[posn]->stir();
+
     // Save the seed if the auto-save timer has expired.
     if ((millis() - timer) >= timeout)
         save();

libraries/Crypto/RNG.h

@@ -35,6 +35,7 @@ public:
     ~RNGClass();
 
     void begin(const char *tag, int eepromAddress);
+    void addNoiseSource(NoiseSource &source);
 
     void setAutoSaveTime(uint16_t minutes);
 
@@ -60,6 +61,8 @@ private:
     uint16_t firstSave : 1;
     unsigned long timer;
     unsigned long timeout;
+    NoiseSource *noiseSources[4];
+    uint8_t count;
 
     void rekey();
 };

libraries/Crypto/RingOscillatorNoiseSource.cpp

@@ -76,15 +76,15 @@
  *     // "MyApp 1.0" and load the previous seed from EEPROM address 500.
  *     RNG.begin("MyApp 1.0", 500);
  *
+ *     // Add the noise source to the list of sources known to RNG.
+ *     RNG.addNoiseSource(noise);
+ *
  *     // ...
  * }
  *
  * void loop() {
  *     // ...
  *
- *     // If the noise source has accumulated new entropy, then stir it in.
- *     RNG.stir(noise);
- *
  *     // Perform regular housekeeping on the random number generator.
  *     RNG.loop();
  *

libraries/Crypto/TransistorNoiseSource.cpp

@@ -56,15 +56,15 @@
  *     // "MyApp 1.0" and load the previous seed from EEPROM address 500.
  *     RNG.begin("MyApp 1.0", 500);
  *
+ *     // Add the noise source to the list of sources known to RNG.
+ *     RNG.addNoiseSource(noise);
+ *
  *     // ...
  * }
  *
  * void loop() {
  *     // ...
  *
- *     // If the noise source has accumulated new entropy, then stir it in.
- *     RNG.stir(noise);
- *
  *     // Perform regular housekeeping on the random number generator.
  *     RNG.loop();
  *

libraries/Crypto/examples/TestRNG/TestRNG.ino

@@ -29,6 +29,9 @@ void setup() {
     // Initialize the random number generator.
     RNG.begin(RNG_APP_TAG, RNG_EEPROM_ADDRESS);
 
+    // Add the noise source to the list of sources known to RNG.
+    RNG.addNoiseSource(noise);
+
     startTime = millis();
 }
 
@@ -58,9 +61,6 @@ void loop() {
             Serial.println("calibrating");
     }
 
-    // If the noise source has accumulated new entropy, then stir it in.
-    RNG.stir(noise);
-
     // Perform regular housekeeping on the random number generator.
     RNG.loop();