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posted by janrinok on Saturday April 20 2019, @11:10AM   Printer-friendly
from the schschschschschschschsch dept.

Famed hardware hacker Bunnie Huang has posted an overview of his notes on designing an open source entropy generator. His summary links to the full notes which include schematics, measurement results, as well as other key details.

The final optimized design takes <1cm2 area and draws 520uA at 3.3V when active and 12uA in standby (mostly 1.8V LDO leakage for the output stage, included in the measurement but normally provided by the system), and it passes preliminary functional tests from 2.8-4.4V and 0-80C. The output levels target a 0-1V swing, meant to be sampled using an on-chip ADC from a companion MCU, but one could add a comparator and turn it into a digital-compatible bitstream I suppose. I opted to use an actual diode instead of a NPN B-E junction, because the noise quality is empirically better and anecdotes on the Internet claim the NPN B-E junctions fail over time when operated as noise sources. I'll probably go through another iteration of tweaking before final integration, but afaik this is the smallest, lowest power open-source avalanche noise generator to date (slightly smaller than this one [PDF]).


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  • (Score: 0) by Anonymous Coward on Sunday April 21 2019, @01:44AM (3 children)

    by Anonymous Coward on Sunday April 21 2019, @01:44AM (#832816)

    Using a zener diode in avalanche breakdown mode for a RNG is a REALLY OLD idea.
    Isn't it surprising then that Huang doesn't cite any previous circuit designs (of which there are many) when he presents "his" design?
    How does it differ from the others in meaningful ways? So I agree with you; Huang presents his done-to-death circuit as something new and innovative.

  • (Score: 2) by janrinok on Sunday April 21 2019, @09:16AM (2 children)

    by janrinok (52) Subscriber Badge on Sunday April 21 2019, @09:16AM (#832894) Journal

    He explains why he did it in his notes:

    I had to do a new design because the existing open-source ones I could find were too large and power hungry to integrate into a mobile device.

    You asked "How does it differ from the others in meaningful ways?" and the question had already been answered.

    • (Score: 0) by Anonymous Coward on Sunday April 21 2019, @05:48PM (1 child)

      by Anonymous Coward on Sunday April 21 2019, @05:48PM (#833042)

      He states other designs were too large and power hungry, but then he does not state which designs he rejected.
      The info is not anywhere to be found in his notes.

      • (Score: 2) by janrinok on Monday April 22 2019, @07:29AM

        by janrinok (52) Subscriber Badge on Monday April 22 2019, @07:29AM (#833290) Journal

        The design of the circuit is irrelevant if building it results in a circuit that is too large to fit his mobile device or drains too much power, although it is true that it might be of interest to some. This was the smallest design that he could build that met his very limited power budget.