Schneier on Security

Clive Robinson • October 11, 2010 7:23 PM

@ Lisa,

“So it would not be unrealistic to expect these agencies to also forged biometrics as well in the near future”

I have at various points in my life worked out how to forge most biometrics, the only major one so far I have not had a go at is iris scanning. Not because I think it might not be possible but the cost of getting access to the systems is way to high currently.

The one that makes me smile sadly is DNA we here ludicrous and compleatly unsuported statments from the mouths of “scientists” acting as “expert witnesses”. Their statments of only one in a hundred billion (or whatever) is bassed on the notion of a linear population and an incorect assumption about the test methodology.

As for the linear population how many natural red heads have you seen in the african and asian populations? How many people from european populations have sickle cells? Likewise “genetic illnesses” run in population types. Thus you can safely say that human DNA is not linearly spread across all possible types, even after cross racial breeding.

But as the artical notes people are not researching into these areas possably for the “golden goose” reason.

What makes the issue worse is the assumption that human DNA cannot be cloned, and that this caries forward through the DNA testing process. It does not, many years ago I worked out how to game the DNA test by seeding a crime scene (I’ve posted the outline of how to do it in the past). It is only in recent times (the last three years or so) some scientests have worked out a way to stop the simple gaming. Unfortunatly there are more complex ways to still do it.

Originaly I contacted people involved in DNA work and pointed out that it could be gamed. The response in all cases was to deny it was possible and when you asked if they had ever tested the hypotheses they either refused to answer or filibustered. The question is as to why… I concluded that they did not want to “kill the golden goose” or they enjoyed the idea of wearing “emperors new clothes”. However a scientist in Australia some years later did the tests (as far as I’m aware compleatly unknowing of anything relating to me and my questions) and showed conclusivly that DNA testing could be gamed and thus results falsified.

I was faking fingerprints over forty years ago with common household items (soft red wax from edam cheese, WD40 oil, rubber solution glue). I came up with the idea after reading a Sherlock Holmes story.

BUT IMPORTANTLY all thes problems with biometrics happen in all forms of “forensic science” for instance bullet metal alloy analysis where it was argued for some time that you could tell from the alloy composition if a bullet at a crime scene came from the same batch as those found in a persons gun cupboard etc. Expert witnesses who had never tested the idea jumped on the band waggon. Then a scientist went an analysed the alloy across several batches and found the idea of alloy matching was compleat bunkum, when analysing bars of the metal alloy prior to making bullets he found the variation in the bar to vary wildly beyond any possable level of confidence.

One issue that is biting hard is the notion of “noise” or “background contamination” some tests are so sensitive that the probability of them showing a chemical present is very high. This is because nearly all the chemicals forensic examiners look for are “naturaly in the environment”. An early example of this was the “aunt aggies bomb factory” a group of irish people where arrested and accused of bomb making because traces of certain explosives where found on their hands.

Well it turns out that the explosive concerned is a byproduct of the natural decay of certain celulose plastics. The fact that this was known to happen from a hundred years before hand with “exploding billiard balls” was not brought to the juries attention. Thus a totaly false conviction was obtained.

My view is that forensics is most definatly not nor can it ever be a science in the traditional sense. The best it can do is make probablistic statments about physical objects found at a crime scene etc. It cannot say how something came about.

An example of this was told to me by one of our “learned friends” a clear finger print had been recovered from a beer glass used to seriously attack somebody. It turns out the fingerprint (in all probability) was a 100% match to a person who was picked up and accused. It was only after they could show a very very solid alibi and no real motive could be found that the forensics came into question.

It turns out that the suspect had drunk at the pub some months beforehand, and the pub washed it’s glasses using those little bar edge washing machines that clean the inside and top of the outside but not the base of the glass because the bar staff hold this end of the glass when using the washing machine. Thus the forensics were in all probability correct it was the interpretation of the information provided that was incorrect.

Clive Robinson • October 12, 2010 6:02 PM

@ Roger,

“I understand that in fact the lab had cut costs by sourcing supplies that were never intended for forensic applications”

Which lab the one making the swabs or the forensic lab? your comment can be read either way.

As I recall it was an own goal for the forensic lab that decided to switch from “DNA free” to “sterile” swabs which where many time cheaper. What is not clear is why (ie a non scientist admin type making assumptions etc).

@ Salach,

“The question is not if it is easy to forge but a much more severe problem is the false identification from errors or contamination, without anyone actively forging DNA”

Yes it’s a part of the more general “noise” issue I refered to that. criticaly effects all forensic tests.

However from my point of view the ultimate fail of DNA forensics is when you can pull a chosen individuals DNA profile out of a Government or NGO DB and synth up the required partial bits to show a positive identification in the current testing framework without setting off alarms.

@ greg,

“We have good protocols to detect contamination these days.”

Atleast one was developed by the Australian I refered to in my post.

That being said, it’s been a few years since I last looked into what was required to game a forensic DNA test, so I’m out of touch with what can and can not currently be done. For instance there where newspaper reports not so long ago that a scientist had created his own “living” bacteria from non living DNA he had synthed up. The truth of it seamed improbable from the way it was reported by journos.

With regards synthing up to game the current DNA testing with it’s controls, many of these controls are add ons to look for quite specificindicators. I suspect if you and your colleagues sat down with pizza and a few beers and had a “what if” rump session you could fairly readily identify promissing avenues of investigation that would game a forensic DNA test even with the current check additions.

The reason I feal this, is the “if you break it once, you can break it again” issue. That is adding a test for a specific break only buttresses up one small part of the process, the chances are good there are many other vectors. That is as you add more check tests it is likley it will fail under the weight of these add on tests.

For example, If people think back to the Fast Encryption Algorithm (FEAL). It got broken, fixed, broken again, fixed again, over and over again. Each time the attack got better till eventually a compleatly new method of attack arose that broke many crypto algorithms.