Entries Tagged "biometrics"

Page 12 of 17

DNA Matching and the Birthday Paradox

Nice essay:

Is it possible that the F.B.I. is right about the statistics it cites, and that there could be 122 nine-out-of-13 matches in Arizona’s database?

Perhaps surprisingly, the answer turns out to be yes. Let’s say that the chance of any two individuals matching at any one locus is 7.5 percent. In reality, the frequency of a match varies from locus to locus, but I think 7.5 percent is pretty reasonable. For instance, with a 7.5 percent chance of matching at each locus, the chance that any 2 random people would match at all 13 loci is about 1 in 400 trillion. If you choose exactly 9 loci for 2 random people, the chance that they will match all 9 is 1 in 13 billion. Those are the sorts of numbers the F.B.I. tosses around, I think.

So under these same assumptions, how many pairs would we expect to find matching on at least 9 of 13 loci in the Arizona database? Remarkably, about 100. If you start with 65,000 people and do a pairwise match of all of them, you are actually making over 2 billion separate comparisons (65,000 * 64,999/2). And if you aren’t just looking for a match on 9 specific loci, but rather on any 9 of 13 loci, then for each of those pairs of people there are over 700 different combinations that are being searched.

So all told, you end up doing about 1.4 trillion searches! If 1 in 13 billion searches yields a positive match as noted above, this leads to roughly 100 expected matches on 9 of 13 loci in a database the size of Arizona’s. (The way I did the calculations, I am allowing for 2 individuals to match on different sets of loci; so to get 100 different pairs of people who match, I need a match rate of slightly higher than 7.5 percent per locus.)

EDITED TO ADD (9/14): The FBI is trying to suppress the analysis.

Posted on September 11, 2008 at 6:21 AM • View Comments

Gait Analysis from Satellite

Ignoring the sensationalist headline, this is interesting:

By analysing the movements of human shadows in aerial and satellite footage, JPL engineer Adrian Stoica says it should be possible to identify people from the way they walk—a technique called gait analysis, whose power lies in the fact that a person’s walking style is very hard to disguise.

Video taken from above shows only people’s heads and shoulders, which makes measuring the characteristic length and rhythm of a person’s stride impossible. That’s not true of shadows, though, Stoica told a security conference in Edinburgh, UK, last month. Shadows, he says, provide enough gait data to deduce a positive ID. To prove it, he has written software that recognises human movement in aerial and satellite video footage. It isolates moving shadows and uses data on the time of day and the camera angle to correct shadows if they are elongated or foreshortened. Regular gait analysis is then applied to identify people. In tests on footage shot from the sixth floor of a building, Stoica says his software was indeed able to extract useful gait data.

The article goes on to say that using satellite images would be harder, but that the basic idea is the same.

Of course, this is less useful for finding individuals and more useful for tracking a population as it moves about its day. But some individuals will have more distinctive gaits than others, and will be easier to track. Soon we may all need to walk with rocks in our shoes.

Posted on September 9, 2008 at 12:22 PM • View Comments

Chertoff Says Fingerprints Aren't Personal Data

Homeland Security Secretary Michael Chertoff says:

QUESTION: Some are raising that the privacy aspects of this thing, you know, sharing of that kind of data, very personal data, among four countries is quite a scary thing.

SECRETARY CHERTOFF: Well, first of all, a fingerprint is hardly personal data because you leave it on glasses and silverware and articles all over the world, they’re like footprints. They’re not particularly private.

Sounds like he’s confusing “secret” data with “personal” data. Lots of personal data isn’t particularly secret.

Posted on April 21, 2008 at 6:54 AM • View Comments

German Minister's Fingerprint Published

This is 1) a good demonstration that a fingerprint is not a secret, and 2) a great political hack. Wolfgang Schauble, Germany’s interior minister, is a strong supporter of collecting biometric data on everyone as an antiterrorist measure. Because, um, because it sounds like a good idea.

Here’s the story directly from the Chaos Computer Club (in German), and its Engligh-language guide to lifting and using fingerprints. And me on biometrics from 10 years ago.

Posted on April 1, 2008 at 2:37 PM • View Comments

Improvements in Face Recognition

Ignore the laughable “100% accurate” claim; this is an interesting idea:

Mike Burton, Professor of Psychology at Glasgow, and lecturer Rob Jenkins say they achieved their hugely-improved results by eliminating the variable effects of age, hairstyle, expression, lighting, different camera equipment etc. This was done by producing a composite “average face” for a person, synthesised from twenty different pictures across a range of ages, lighting and so on.

Not useful when you only have one grainy photograph of your target, but interesting research nonetheless.

Posted on February 11, 2008 at 7:18 AM • View Comments

Interesting Twist on Identity Theft

Okay, this is clever.

Basically, someone arrested as a homicide suspect walked out of jail after identifying himself as someone else. The biometric system worked, but human error overrode it:

But Sauceda’s fingerprints, taken by a jail employee to verify his identity, were smudged and couldn’t be matched to those on file for Garcia, said Brian Menges, director of jail administration.

So Sauceda was taken for an additional fingerprint check using the jail’s Live Scan technology. Menges said Saucedo’s Live Scan fingerprints were never compared to those on record for Garcia.

It’s a neat scam. Find out someone else who’s been arrested, have a friend come and post bail for that person, and then steal his identity when the jailers come into the cellblock.

Posted on November 2, 2007 at 12:25 PM • View Comments

Partial Fingerprints Barred from Murder Trial

Brandon Mayfield, the Oregon man who was arrested because his fingerprint “matched” that of an Algerian who handled one of the Madrid bombs, now has a legacy: a judge has ruled partial prints cannot be used in a murder case.

“The repercussions are terrifically broad,” said David L. Faigman, a professor at the University of California’s Hastings College of the Law and an editor of Modern Scientific Evidence: The Law and Science of Expert Testimony.

“Fingerprints, before DNA, were always considered the gold standard of forensic science, and it’s turning out that there’s a lot more tin in that field than gold,” he said. “The public needs to understand that. This judge is declaring, not to mix my metaphors, that the emperor has no clothes.”

Posted on October 25, 2007 at 7:03 AM • View Comments

More Behavioral Profiling

I’ve seen several articles based on this press release:

Computer and behavioral scientists at the University at Buffalo are developing automated systems that track faces, voices, bodies and other biometrics against scientifically tested behavioral indicators to provide a numerical score of the likelihood that an individual may be about to commit a terrorist act.

I am generally in favor of funding all sorts of research, no matter how outlandish—you never know when you’ll discover something really good—and I am generally in favor of this sort of behavioral assessment profiling.

But I wish reporters would approach these topics with something resembling skepticism. The false-positive rate matters far more than the false-negative rate, and I doubt something like this will be ready for fielding any time soon.

EDITED TO ADD (10/13): Another comment.

Posted on October 15, 2007 at 6:16 AM • View Comments

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Sidebar photo of Bruce Schneier by Joe MacInnis.