Schneier on Security

Clive Robinson • April 6, 2010 7:52 PM

@ greg,

“So is it reflecting just off/internally to the lens, or through the full optics path (ie back of the sensor)?”

I’m not sure at which end you are talking about. So,

The full path,

Starting at the EM source:
1,Coherent EM Source,
2,Beam spread collimator,
3,Half silvered mirror (directional coupler),
4,Beam reduce collimator,
5,Fast prism,
6,Slow prism,
7,Primary lens structure (to give wider field of view/coverage).

Outbound into free space,

Then at the observer/snipers end (ie a refracting telescope):
A,Primary/Objective lens structure,
B,Focal lens beam spread collimator,
C,Focal lens,
D,Human eye lens,
E,Vitreous body,
F,Photoreceptors (rods/cones) in retina.

Now if all of this is in focus (ie observer/sniper is actually looking at the target the EM source is mounted on) you get the red eye effect. That is the coherant EM source will be focused onto the retina and will reflect back through 180 degres (give or take a fraction) and return along the same path but in reverse untill it meets the half silvered mirror that is used as the directional coupler where the return path beam is directed through another collimator and onto your photo detector array.

This photo detector array (CCD detector) is where all the good stuff is done with optical filters etc to obtain the maximum optical information, before the relavant signals hit the DSP’s to extract other information.

For instance with more than a single frequency EM source, it is possible to enumerate (detect) the different substances at the focal point where the 180 degree reflection takes place.

Thus you can tell not only if it’s a silicon / galium / human retina as the sensor, it is possible to “image” which part of the retina is being used (rods and cones have different reflection spectra).

Also it should be possible to measure the response time etc of the eye which is supposed to be not just a secondary (to the retina) “unique bio-metric”, but potentialy an “at a distance medical diagnostic” indicator of heart rate, blood oxygenation, core body temprature, stress levels etc etc.

Although I’m somewhat doubtfull if there would be sufficient signal to noise on some of the medical diagnostic signals at any significant range (say no more than a couple of hundred feet tops).

The reason I mention the medical diagnostics is there have been some claims (for research funding) that the medical diagnostic potential of some “at a distance retina scanners” can be used as duress / lie detectors, as well as a method of determaning “ill health” in airports etc to detect the likes of SARS etc…

And thus it is (signal to noise permitting) a logical follow on in the technology also I mention it to scupper any non US potential patent claims as it is now known and thus “prior art” (sadly in the US there are “submarine patents” which I have yet to see the good of so I expect this to be hitting a US patent clerk any time real soon…).

Clive Robinson • April 7, 2010 10:05 AM

@ Robert,

In addition to gregs points the orthaganality of such systems have advantages when several systems are used together and their “view fields” overlap. As would be quite likely in a convoy etc where vehicals had independant systems.

You also need to think about other aspects such as “offset LIDAR” etc.

Although Gold codes are very good they can be slow to “lockup” when starting from cold on an unknown long sequence.

So also have a think about NASA JPL (Jet Propulsion Labs) Ranging codes, they have similar orthaganality but as they are made of short Gold codes can lock up in much much shorter time periods.

The question of,

“I’m thinking of heat bending the light beam”

Is a curious one and I’m assuming you have some knowledge of heat lenses.

More pragmaticaly however it is not unknown for ranging systems to use two coherant but orthagonaly polarised and modulated EM sources. The reasons are a bit complicated but if you have a read up on weather lidar/radar it will give you a starting point as to the physics (have a trawl therough the optinfobase on lidar for some of the details).

Put simply you can measure wind direction and other things of interest for “auto gun laying”, which if you think about it is the next stage of dealing with an identified hostile.

Clive Robinson • April 7, 2010 11:50 PM

@ Robert,

“I was assuming that code synchronization would be done optically using a Kerr or Pockel cell, but I guess you don’t need to modulate the source that quickly”

That’s a point to you on the technology side, now I understand why you said,

“My minds working overtime trying to figure out what application needs this functionality…”

We’re thinking more than a few orders of magnitude different in range resolution capability.

I’ll put my hand up and say I had not even considered this way, simply because the last time I looked the technology was a tads expensive and fragile.

But I would definatly be interested in hearing your guestimate on (uncased) BOM on your system, as technology “sweet spots” are always on the move.

This is because despite what various Politicos say to the press and House of Commons Select commities, the bitter truth is the likes of the UK MOD procurment people are looking for “as cheap as chips” throw away technology these days.

All delivered to the battle front by the likes of DHL/TNT/UPS (belive it or not, tanks and other heavy armor where being transported by drivers working for “Blue Arrow” not so long ago).

Thus I’d be the first to admit the system I was thinking of would use a very cheap but robust optical head, that with say a very minor change in the case and primary lens could also have a myriad of uses such as civil engineering. The back end being all software on COTS hardware. Think about the history of GPS and what sort of GPS equipment squadies get issued with these days to see why I’m think that way.

As you say,

“I guess the best solution depends on which technology you are more comfortable with.”

A little history explains my sometimes odd outlook 😉

I moved out of MilSpec design quite a while ago as I could see the writing on the wall. The wake up call was at a retirment party, the retiring person told me that they had spent a quater of a century as a projects manager on just one MilSpec project. And I can clearly remember thinking about how the likes of Intel and AMD where slugging it out on 18month product lifetimes.

It was clearly not sustainable and it’s what made me get out of that sort of design. Via an odd route I ended up doing Fast Moving Consumer Electronics (FMCE) design for personal communication (phones amongst other things).

But even there I saw the writing on the wall with even shorter product design and life cycles.

And again it came back to me with the first Gulf war and failing comms equipment and tentative enquiries for MilSpec or Hardend mobile phone systems. Needless to say the “old guard” won out. But look at the reality of today, squadies find they get better coverage on the battle field with their personal mobile than they do with their “MilSpec Comms equipment”. Likewise the UK’s Met Police with their comms systems.

The joke of it is the longest hardware project life cycles these days are to be found in the Civil airframe, Telco Infrastructure and civil space technology industries. Where the recent economic slump has started people taking a good long hard look at cutting upgrade cycles to about a half what they where, thus nearly trippling life expectancy and availability requirments, there’s 747’s flying comercialy with something like 30+ years on the airframe, and no plans to retire them.

It’s why I’m looking at the likes of Software Defined Radio (SDR) on consumer grade electronics in high availability configs. I suspect it’s the way it’s got to go to keep up with expectations.

Oh and of course as “software for everything” applies to critical infrastructure like mobile phone base stations, we need real software security right down through the OS etc and below layer 0 on the software stack and well into digital hardware that would have been the domain of analoge electronics just ten years ago.

It’s why Nick P is looking at “secure by design” CPU’s for the likes of I/O control, and I’m looking a little further into the future by thinking on how to put multiple “prisons cells” on the chip. Just to protect the RF amp, Down Convert, DSP control systems on that Government Mandated box that controls your home energy usage for the next thirty years…

Clive Robinson • April 8, 2010 5:54 PM

@ GreenSquirrel,

“In general terms then, am I right in thinking that this is a system that can detect a camera only in the act of taking a picture?”

Depends what you mean by “taking a picture”.

For an old fashioned film camera you have a shutter that would in most cases stop the 180 degree reflection as the focal point is interupted (however there is a reason why the lens side of the shutter is painted mat black and that’s multiple reflections).

However the view finder is still acting as a “telescope” so when the eye is behind the eye piece the retina will be the 180 degree reflecting point.

So film cameras are the same as real SLR’s.

However, most digital camera’s including most Digital SLR’s have a sensor always in the optical path at (one of) the focal point(s), so nearly all digital cameras will be detected when pointing at the detector.

As I’ve indicated this is not exactly a new idea, and Bruce actual bloged about a system to stop photos being taken at exhibitions and trade fairs which not only detects the camera but in the case of film cameras can actually fire a bright light into the camera optics effectivly blinding it with lens flare etc.

As I said at the time it would be interesting to see what such a system would make of “clear water” LED’s (as found in most LED flashlights) which are effectivly a clear lens with a lump of polished silicon at the focal point…