[onerng talk] The world's (other) most secure TRNG

[Paul Campbell]

On Mon, 29 Sep 2014 19:25:31 Bill Cox wrote:
> I've been trying to bread-board it.  The freaking surface mount parts are
> holding me back at the moment.  I've got a $100 purchase of Digikey parts
> mounted on Proto Advantage adapters, but it's expensive and slow!

actually I've gone completely surface mount - startup is expensive (tool wise) 
but all the cheap stuff from China has made that completely doable 

I buy by the reel these days - I use Dirty PCBs for proto boards at the 
moment: http://dirtypcbs.com/  - they're good people 

> > if you need help finding cheap and easy ways to build prototype
> > boards I can help point you at cheap stuff in China - or we could spin a
> > version of my board with your RNG on it as a proof-of-concept.
> 
> I would love to know how to get stuff built cheaply!  Please let me know.
> I was about to start Googling Arduino projects to see if I could find out
> what's the best way now days.

well I bought a cheap pick-and-place, I do my own prototypes (I was thinking 
of PCB boards), I wouldn't manufacture in volume though - but you don't really 
need it, you can too with just a cheap chinese reflow oven, either get solder 
stencils made or just drop solder from a syringe on to pads - then place parts 
by hand - then run it thru the oven the results look as good as commercially 
made stuff

Actual production in the 1000s means going to China .... that's a whole other 
story

> I built a zener-noise TRNG back in 1998, with reverse Vbe breakdown of a
> 2N2222, and fed it into a 40MHz 8-bit A/D converter, and used a Lattice
> FPGA to whiten the output.  The A/D converter was my first ever experience
> with surface mount parts, and I've mostly given up on prototyping since.
> 
> I would be very happy to work with you on a proof-of-concept built on your
> board.  That would be awesome.

maybe once you have a working prototype?

> This was designed for Triad Semiconductor's 0.35u mixed signal ASICs.  They
> have capacitor arrays and transistor arrays, and the whole thing is
> configured with one via layer.  I think the mixed-signal ASIC guys in
> general would disagree that analog in CMOS is a bad idea... however, it is
> in an analog process.
> 
> Noise is good.  Power supply noise, shot noise, 1/f noise, thermal noise,
> and even Mallory's external RF signal injection are all welcome!  They all
> get mashed together and add to entropy, rather than overriding it.  That's
> what happens when we amplify with modular multiplication rather than
> saturating multiplication.

OK a bit of a different process ... 

I was more thinking of noise injected synchronously  due to your clock, VDD 
will droop due to pin inductance as everything switches (you might attach any 
spare internal caps to VDD if you can)

 
> > than the avalanche source, largely because the analog avalanche source is
> > being sampled in the analog domain and getting a perfect sample means
> > choosing
> > a sampling point and that likely means hand tweaking resistors in the
> > manufacturing process - instead we just accept that we get 7.5 bits of
> > entropy/byte and 'whiten' it through a CRC.
> 
> That's the right approach, IMO.  Just feed unpredictable state into your
> entropy pool and generate as much data from it as you need.

and that's the way  the linux kernel works - you just have to feed it data 
that's  random enough to pass it's smoke test (hence the small amount of 
whitening)


> > Besides that these designs are not ones one normally builds, after years
> > of building stuff to discourage noise actually making it on purpose, and
> > then
> > trying to contain it means that you are by definition going to have FCC
> > issues
> > - I think you need an RF shield no matter what you do.
> 
> I agree.  I'll need to keep the EMI where it belongs - on the inside of the
> USB stick.  By the way, while I may need to tweak the design after playing
> with real hardware, the architecture will work.  Here's the unfinished list
> of parts with their cost that I have so far:
> 
>   Quad analog switch 1.3566 1000 1 1.3566  Quad op-amp 1.8 1000 1 1.8 
> 384-LUT FPGA $1.31 1000 1 $1.31  USB interface IC $1.58 1000 1 $1.58  .1uF
> bypass cap 0.0405 1000 1 0.0405  100pF chip cap 0.022 1000 2 0.044  120 Ohm
> 5% resistor 0.01566 1000 2 0.03132  Quad 8.2K 5% resistors 0.01568 1000 1
> 0.01568  Quad 10K 5% resistors 0.01568 1000 1 0.01568

BTW don't forget that to build a real product it also means you have to build 
a manufacturing programming and test jig - that's often as much work as 
designing the product itself

	Paul