[Cryptech Tech] User auditable hardware entropy source/random number generator

[Benedikt Stockebrand]

Hi Fredrik and list,

I'll keep the longer stuff, especially with regard to Bernd's latest
posting, until I've done some more testing, but as for this:

Fredrik Thulin <fredrik at thulin.net> writes:

> Hmm? You mean you are using an off the shelf charge pump circuit rather than a 
> diodes-and-caps voltage doubler, like the Dickson doubler [1] [2]?

Not a charge pump but a boost converter---USB +5V may not be stable
enough for a charge pump.  I use an MC34063, with the externals chosen
such that it works until the brownout detector in the Atmel triggers
anyway.

But this isn't cast in stone; this stuff is modular enough I can use
whatever suitable source I can find, and I've already used others.  If
you have a better idea, please let me know.

> Very much looking forward to more details about your circuit =).

OK, but you've explicitly asked for it...

The first circuit is what I used for the previous tests.  Problem is
that the second transistor is susceptible to saturation, so this has to
be matched to the particular Zener diode used and I still had to use a
high frequency transistor (BF959).  I've kept the step-up converter
board, though.

The current circuits aren't yet merged into a single schematic, and they
are only for the "generator core" (Zener and first stage transistor) and
a an updated "amplifier stage".  Anyway, with this I can hook up either
one or two amplifier stages between the generator core and the MCU, and
I don't have to adjust the gain of the transistor stages any longer
thanks to the BAT85.

What's missing is the MCU/FT232RL combo, the step-up converter and
generally some more attention to the power supply part: If several of
these things are run from a single >= +12V supply, then they should each
have their own LC filter to avoid correlating them.  And so far I don't
correctly separate the +5V from the USB port and the LC-filtered +5Vs
for the MCU and amplifier stages.

More on that after I've got some proper performance results on the
various Zener diodes etc.


Cheers,

    Benedikt

PS: Is it OK to post attachments on this list?  I'd personally rather
    keep the list self-contained, but if you prefer I can also put
    this sort of stuff on my web site.

-------------- next part --------------
A non-text attachment was scrubbed...
Name: OldGeneratorModule.pdf
Type: application/pdf
Size: 13188 bytes
Desc: Old version circuit, only using the step-up converter now
URL: <https://lists.cryptech.is/archives/tech/attachments/20140714/7e4feca9/attachment-0003.pdf>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: GeneratorCore.pdf
Type: application/pdf
Size: 9074 bytes
Desc: "generator core" schematic
URL: <https://lists.cryptech.is/archives/tech/attachments/20140714/7e4feca9/attachment-0004.pdf>
-------------- next part --------------
A non-text attachment was scrubbed...
Name: SingleAmplifierStage.pdf
Type: application/pdf
Size: 7586 bytes
Desc: "single amplifier stage" schematic
URL: <https://lists.cryptech.is/archives/tech/attachments/20140714/7e4feca9/attachment-0005.pdf>
-------------- next part --------------

-- 
Benedikt Stockebrand,                   Stepladder IT Training+Consulting
Dipl.-Inform.                           http://www.stepladder-it.com/

          Business Grade IPv6 --- Consulting, Training, Projects

BIVBlog---Benedikt's IT Video Blog: http://www.stepladder-it.com/bivblog/