/**
* \brief Initializes the random number generator.
*
* \param tag A string that is stirred into the random pool at startup;
* usually this should be a value that is unique to the application and
* version such as "MyApp 1.0" so that different applications do not
* generate the same sequence of values upon first boot.
*
* This function should be followed by calls to addNoiseSource() to
* register the application's noise sources.
*
* \sa addNoiseSource(), stir(), save()
*/
void RNGClass::begin(const char *tag)
{
// Bail out if we have already done this.
if (initialized)
return;
// Initialize the ChaCha20 input block from the saved seed.
memcpy_P(block, tagRNG, sizeof(tagRNG));
memcpy_P(block + 4, initRNG, sizeof(initRNG));
#if defined(RNG_EEPROM)
int address = RNG_EEPROM_ADDRESS;
eeprom_read_block(stream, (const void *)address, SEED_SIZE);
if (crypto_crc8('S', stream, SEED_SIZE - 1) ==
((const uint8_t *)stream)[SEED_SIZE - 1]) {
// We have a saved seed: XOR it with the initialization block.
// Note: the CRC-8 value is included. No point throwing it away.
for (int posn = 0; posn < 12; ++posn)
block[posn + 4] ^= stream[posn];
}
#elif defined(RNG_DUE_TRNG)
// Do we have a seed saved in the last page of flash memory on the Due?
if (crypto_crc8('S', ((const uint32_t *)RNG_SEED_ADDR) + 1, SEED_SIZE)
== ((const uint32_t *)RNG_SEED_ADDR)[0]) {
// XOR the saved seed with the initialization block.
for (int posn = 0; posn < 12; ++posn)
block[posn + 4] ^= ((const uint32_t *)RNG_SEED_ADDR)[posn + 1];
}
// If the device has just been reprogrammed, there will be no saved seed.
// XOR the initialization block with some output from the CPU's TRNG
// to permute the state in a first boot situation after reprogramming.
pmc_enable_periph_clk(ID_TRNG);
REG_TRNG_CR = TRNG_CR_KEY(0x524E47) | TRNG_CR_ENABLE;
REG_TRNG_IDR = TRNG_IDR_DATRDY; // Disable interrupts - we will poll.
mixTRNG();
#endif
#if defined(RNG_ESP_NVS)
// Do we have a seed saved in ESP non-volatile storage (NVS)?
nvs_handle handle = 0;
if (nvs_open("rng", NVS_READONLY, &handle) == 0) {
size_t len = 0;
if (nvs_get_blob(handle, "seed", NULL, &len) == 0 && len == SEED_SIZE) {
uint32_t seed[12];
if (nvs_get_blob(handle, "seed", seed, &len) == 0) {
for (int posn = 0; posn < 12; ++posn)
block[posn + 4] ^= seed[posn];
}
clean(seed);
}
nvs_close(handle);
}
#endif
#if defined(RNG_WORD_TRNG)
// Mix in some output from a word-based TRNG to initialize the state.
mixTRNG();
#endif
// No entropy credits for the saved seed.
credits = 0;
// Trigger an automatic save once the entropy credits max out.
firstSave = 1;
// Rekey the random number generator immediately.
rekey();
// Stir in the supplied tag data but don't credit any entropy to it.
if (tag)
stir((const uint8_t *)tag, strlen(tag));
#if defined(RNG_DUE_TRNG)
// Stir in the unique identifier for the CPU so that different
// devices will give different outputs even without seeding.
stirUniqueIdentifier();
#elif defined(ESP8266)
// ESP8266's have a 32-bit CPU chip ID and 32-bit flash chip ID
// that we can use as a device unique identifier.
uint32_t ids[2];
ids[0] = ESP.getChipId();
ids[1] = ESP.getFlashChipId();
stir((const uint8_t *)ids, sizeof(ids));
#elif defined(ESP32)
// ESP32's have a MAC address that can be used as a device identifier.
uint64_t mac = ESP.getEfuseMac();
stir((const uint8_t *)&mac, sizeof(mac));
#else
// AVR devices don't have anything like a serial number so it is
// difficult to make every device unique. Use the compilation
// time and date to provide a little randomness across applications
// if not across devices running the same pre-compiled application.
tag = __TIME__ __DATE__;
stir((const uint8_t *)tag, strlen(tag));
#endif
#if defined(RNG_WATCHDOG)
// Disable interrupts and reset the watchdog.
cli();
wdt_reset();
// Clear the "reset due to watchdog" flag.
MCUSR &= ~(1 << WDRF);
// Enable the watchdog with the smallest duration (16ms)
// and interrupt-only mode.
_WD_CONTROL_REG |= (1 << _WD_CHANGE_BIT) | (1 << WDE);
_WD_CONTROL_REG = (1 << WDIE);
// Re-enable interrupts. The watchdog should be running.
sei();
#endif
// Re-save the seed to obliterate the previous value and to ensure
// that if the system is reset without a call to save() that we won't
// accidentally generate the same sequence of random data again.
save();
// The RNG has now been initialized.
initialized = 1;
}
/**
* \brief Initializes the random number generator.
*
* \param tag A string that is stirred into the random pool at startup;
* usually this should be a value that is unique to the application and
* version such as "MyApp 1.0" so that different applications do not
* generate the same sequence of values upon first boot.
* \param eepromAddress The EEPROM address to load the previously saved
* seed from and to save new seeds when save() is called. There must be
* at least SEED_SIZE (49) bytes of EEPROM space available at the address.
*
* This function should be followed by calls to addNoiseSource() to
* register the application's noise sources.
*
* The \a eepromAddress is ignored on the Arduino Due. The seed is instead
* stored in the last page of system flash memory.
*
* \sa addNoiseSource(), stir(), save()
*/
void RNGClass::begin(const char *tag, int eepromAddress)
{
// Save the EEPROM address for use by save().
address = eepromAddress;
// Initialize the ChaCha20 input block from the saved seed.
memcpy_P(block, tagRNG, sizeof(tagRNG));
memcpy_P(block + 4, initRNG, sizeof(initRNG));
#if defined(RNG_EEPROM)
if (eeprom_read_byte((const uint8_t *)address) == 'S') {
// We have a saved seed: XOR it with the initialization block.
for (int posn = 0; posn < 12; ++posn) {
block[posn + 4] ^=
eeprom_read_dword((const uint32_t *)(address + posn * 4 + 1));
}
}
#elif defined(RNG_DUE_TRNG)
// Do we have a seed saved in the last page of flash memory on the Due?
int posn, counter;
if (((const uint32_t *)RNG_SEED_ADDR)[0] == 'S') {
// XOR the saved seed with the initialization block.
for (posn = 0; posn < 12; ++posn)
block[posn + 4] ^= ((const uint32_t *)RNG_SEED_ADDR)[posn + 1];
}
// If the device has just been reprogrammed, there will be no saved seed.
// XOR the initialization block with some output from the CPU's TRNG
// to permute the state in a first boot situation after reprogramming.
pmc_enable_periph_clk(ID_TRNG);
REG_TRNG_CR = TRNG_CR_KEY(0x524E47) | TRNG_CR_ENABLE;
REG_TRNG_IDR = TRNG_IDR_DATRDY; // Disable interrupts - we will poll.
for (posn = 0; posn < 12; ++posn) {
// According to the documentation the TRNG should produce a new
// 32-bit random value every 84 clock cycles. If it still hasn't
// produced a value after 200 iterations, then assume that the
// TRNG is not producing output and stop.
for (counter = 0; counter < 200; ++counter) {
if ((REG_TRNG_ISR & TRNG_ISR_DATRDY) != 0)
break;
}
if (counter >= 200)
break;
block[posn + 4] ^= REG_TRNG_ODATA;
}
#endif
// No entropy credits for the saved seed.
credits = 0;
// Trigger an automatic save once the entropy credits max out.
firstSave = 1;
// Rekey the random number generator immediately.
rekey();
// Stir in the supplied tag data but don't credit any entropy to it.
if (tag)
stir((const uint8_t *)tag, strlen(tag));
#if defined(RNG_DUE_TRNG)
// Stir in the unique identifier for the CPU so that different
// devices will give different outputs even without seeding.
stirUniqueIdentifier();
#endif
// Re-save the seed to obliterate the previous value and to ensure
// that if the system is reset without a call to save() that we won't
// accidentally generate the same sequence of random data again.
save();
}