Entropy source with embedded computing method for true random number generation

Electronic device comprising:

• an entropy source comprising:
• a first ring oscillator and a second ring oscillator identical to the first ring oscillator, and
• a synchronous flip-flop configured to supply an output signal-corresponding to a sampling of an output of the first oscillator at a frequency of an output of the second oscillator;
• a counter configured to supply, for each period of the output signal of the flip-flop, a value equal to a number of periods of the second oscillator-counted during said period of the output signal of the flip-flop;
• a first circuit configured to modify, during a first phase, a period of at least one of the two oscillators based on the values supplied by the counter so that an average difference between the periods of the two oscillators is equal to a target difference;
• and
• a second circuit configured to receive the values supplied by the counter and to characterize, during a second phase and based on said values, an Allan variance on the output of the counter.