add support for esp32c3 on-chip random generator to crypto/rand package. #2123
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I think the current implementation is not safe against predictable numbers. Specifically:
When there is noise coming from the SAR ADC, the random number generator is fed with a 2-bit entropy in one clock cycle of RTC20M_CLK (20 MHz), which is generated from an internal RC oscillator (see Chapter 6 Reset and Clock for details). Thus, it is advisable to read the RNG_DATA_REG register at a maximum rate of 1 MHz to obtain the maximum entropy.
For details on how this can be implemented, see the esp_random function:
https://github.com/espressif/esp-idf/blob/v4.3/components/esp32c3/hw_random.c
That said, adding a RNG like this seems like a good idea (if implemented correctly).
src/crypto/rand/rand_esp32c3.go
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| r := esp.APB_CTRL.RND_DATA.Get() | ||
| a := (*[4]byte)(unsafe.Pointer(&r))[:] |
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This duplicates the r variable, which is a bit confusing. Can you rename the r variable (and possibly other single letter variables) to something more readable?
| // Enable SAR ADC | ||
| esp.SYSTEM.PERIP_CLK_EN0.SetBits(esp.SYSTEM_PERIP_CLK_EN0_APB_SARADC_CLK_EN) |
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It appears that enabling random number generation is a bit more complicated than this:
I'm worried that it is not truly random without this complete initialization.
some info potentially related to RTC20M_CLK2
…at CPU ticks. change local variable names
rename reader type to esp32c3RndReader
The ESP32-C3 contains a true random number generator. This will allow utilize this for cryptographical operations, among other things.