[Cryptech Tech] Alpha Avalanche Noise Block

[Benedikt Stockebrand]

Hi folks,

(catching up on things once again...)

Павел Шатов <meisterpaul1 at yandex.ru> writes:

> On 14.04.2015 21:00, Fredrik Thulin wrote:
>> On Tuesday, April 14, 2015 02:51:56 AM Павел Шатов wrote:
>>> On 13.04.2015 9:55, Fredrik Thulin wrote:
>> Boards such as my STM32 based ones, or stand alone noise boards for the
>> Novena. It might not be that the Cryptech project is interested in building
>> more of these, but others might from our designs.

:-)

>> Based on transparency and audit-ability I would prefer the same components to
>> be used in simple as well as advanced designs, but not if the drawbacks
>> outweigh the benefits of course.

Just for the records: Fredrik and I have had a bit of a chat last
weekend, and I guess my personal interest in finding out how far one can
push auditability, and DIY, and MIY (modify-it-yourself:-) possibilities
while still maintaining some level of usability took some influence on
him.

At the troopers last month in Heidelberg I've done a presentation on
crypto hardware and auditability; video is now available as
https://www.youtube.com/watch?v=Z_i8EBtnz00 in case you're interested in
my particular mindset and some more background.

>>> Speaking of DC/DC converters, they can be divided into three general
>>> types. The first type includes bare controllers. They are very small and
>>> cheap, because they contain only control circuitry, they require several
>>> external components (power switch, inductor, diode, capacitors). They
>>> are typically used when large output current is required. Since we need
>>> only about 50 mA, we don't need this type of converter.
>>>
>>> Converters of the second type have control circuitry and internal power
>>> switches. They still require external inductor, diode and capacitors,
>>> you also have to do some math to calculate required inductance value.
>>> These converters require prototyping, because you must check that you've
>>> selected appropriate inductor.

for completeness sake: The MC34063 I've used falls into the first two
categories, depending on exactly how you use it (with or without
external power transistor, that is).

> Speaking of voltage required for avalanche effect, you should consider
> part-to-part parameter variation. Transistors are analog components,
> if you buy ten BC818 transistors, they will all have different DC
> current gain. Because of this, if you have 10 identical boards, they
> may require slightly different voltages for avalanche effect.

The analog circuitry we're using is supposed to be largely unsusceptible
to these issues.  Depending on the exact avalanche component you use
there are differences in throughput, but the circuit is largely designed
to be self-adapting to component tolerances: 

The voltage for the avalanche component is self adapting, the AC
coupling between the first and second transistor suppresses all
differences in DC signal levels, and eventually the Schmitt trigger
towards the digital input (separate or within an MCU) and the extraction
algorithm make this circuit about as robust with regard to component
tolerances as I could make it.

Remember that this isn't some sort of HiFi analog gear; the overall goal
at the end is to provide near rail-to-rail output, and that's why it's
somewhat unlike (more primitive than) various textbook circuits.


Cheers,

    Benedikt

PS: Fredrik also told me there's a meeting in Prague prior to the next
    IETF; I have to do a training until friday night, but I'll see if I
    can make it by saturday morning.  Talking about mindsets on a
    mailing list is tedious business...

-- 
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/