This function leads to a pretty good spread of values, and seems random enough, even without the biasing. You no longer need bitOut() from the previous code, and that removes the two static longs used in that function, for eight bytes of valuable memory saved. return value with 'noOfBits' random bits set The result? A simple, somewhat random, but biased option is the following code: unsigned long seedOut(unsigned int noOfBits) According to the Wikipedia article on hardware random number generators, it qualifies as random, but is still in need of debiasing (turns out that ‘unbias’ is not the proper term!) It’s based on not the change in values, but simply the least significant bit of each value, which fluctuates considerably. One big result of the responses: a second, simpler way to generate the numbers. Random value between 0 and UINT32_MAX void esp_fill_random ( void * buf, size_t len ) įill a buffer with random bytes from hardware RNG.After my previous article on Random numbers I posted on the Arduino forum looking for similar experiences. This delay is very short (always less than 100 CPU cycles). This function automatically busy-waits to ensure enough external entropy has been introduced into the hardware RNG state, before returning a new random number. In other situations, if true random numbers are required then consult the ESP-IDF Programming Guide “Random Number Generation” section for necessary prerequisites. If Wi-Fi or Bluetooth are enabled, this function returns true random numbers. Get one random 32-bit word from hardware RNG. API Reference Header File Ĭomponents/esp_hw_support/include/esp_random.hįunctions uint32_t esp_random ( void ) If an application requires a source of true random numbers but it is not possible to permanently enable a hardware entropy source, consider using a strong software DRBG implementation such as the mbedTLS CTR-DRBG or HMAC-DRBG, with an initial seed of entropy from hardware RNG true random numbers. The function bootloader_random_disable() must be called to disable the entropy source again before using ADC, I2S, Wi-Fi or Bluetooth. To re-enable the entropy source temporarily during app startup, or for an application that does not use Wi-Fi or Bluetooth, call the function bootloader_random_enable() to re-enable the internal entropy source. However, after the app starts executing then normally only pseudo-random numbers are available until Wi-Fi or Bluetooth are initialized. Startup ĭuring startup, ESP-IDF bootloader temporarily enables a non-RF entropy source (internal reference voltage noise) that provides entropy for any first boot key generation. If none of the above conditions are true, the output of the RNG should be considered pseudo-random only. Consult the ESP32 Technical Reference Manual > Random Number Generator (RNG) chapter for more details. When any of these conditions are true, samples of physical noise are continuously mixed into the internal hardware RNG state to provide entropy. This is because the default ESP-IDF bootloader implementation calls bootloader_random_enable() when the bootloader starts, and bootloader_random_disable() before executing the app. While the ESP-IDF Second stage bootloader is running. Wi-Fi or Bluetooth are enabled).Īn internal entropy source has been enabled by calling bootloader_random_enable() and not yet disabled by calling bootloader_random_disable(). The hardware RNG produces true random numbers under any of the following conditions: ESP32 contains a hardware random number generator, values from it can be obtained using the APIs esp_random() and esp_fill_random().
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