Schneier on Security

Clive Robinson • October 3, 2022 8:07 AM

@ Bruce, ALL,

Re : Arms race on fakes

“This is, of course, not the last word. Deepfake generators will figure out how to use these techniques to create harder-to-detect fake voices. And the deepfake detectors will figure out another, better, detection technique. And the arms race will continue.”

And it’s not that hard to see how. From the article,

“We did the reverse. By inverting many of these same techniques, we were able to extract an approximation of a speaker’s vocal tract during a segment of speech. This allowed us to effectively peer into the anatomy of the speaker who created the audio sample.”

Note that the “approximation” is just from the acoustic information.

Although quite different in detail, it can be seen that if you have a face and profile image of the speaker you can come up with an “approximation” of the alledged speakers vocal tract.

So even if the deep fake “audio approximation” is within “human constraints”, how well will it align with the alleged individuals “image approximation”?

Probably not that well without a lot of work.

However it will get more fun with “video” as in men certainly the movment of the Adams Apple is sufficiently clear to make a dynamic model…

As back in the days of the ECM ECCM… Arms race the question is not realy how far can it go technically but the resource costs involved.

But also consider that a similar analysis will enable deep fake videos to be unmasked. That is if you have a known genuine audio of a speaker you can build a model, then articulate it with the video audio track and compare to the video image of the audio tract.

It is certain that as the bit resolution and scan rates of audio, image and video recordings increases things like “blood flow to emmotion” and much else will fall under scruitiny for deep-fakes. One that should be easy to do is examine the “eye response to artificial lighting”, another “head movments to background noise”.

If people remember back, in the UK quite a few years back, an audio recording was shown to be fake because the very low level “mains hum” did not align with the time claimed and the “National Grid” records.

I think people would be supprised at the amount of research in this area is going to appear over the next few years.

Primarily at the moment it’s fairly easy to “make your name” as there is minimal academic competition, but that will change with just the publication of one or two papers.

Clive Robinson • October 6, 2022 5:01 AM

@ SpaceLifeForm, EvilKiru, lurker, ALL,

“If there is no Witness Creator that can Prove they created the Bag of Bits, then the Bag of Bits is just Digital Hearsay.”

But how does the “creator” “prove” to others that,

1, They were the creator.
2, Nobody else created it.

That in turn needs a “root of trust” bag of bits, that has to remain secret to the “creator” but also “provable” as a “witness” to all others without compromising the “root of trust”.

So now we need a second “witness” back of bits…

The trick we use currently is to actually have the “root of trust” bag of bits be constructed from two –or more– other secret bags of bits, with certain mathmatical properties by the use of a “One Way Function”(OWF). And via a second OWF the “witness”, so the two OWF’s have to be mathmaticaly related.

That is you have two sets X and Y and they are of the same size and they uniquely map (bijective) from the members of one set to the member of the other set. The first OWF E provides the map from the members “x” of the first set X to the members “y” of the second set Y, the second OWF D provides,the inverse map. So,

y = E(x) and x = D(y)

Respectively. Even without the use of any mathmatical proofs most can see that there are more ways to make the mapping E than there are members in the the set X. Which is usefull because you need that to make the OWFs generally usefull. So you end up with,

y = E(ek,x) and x = D(dk,y)

Where ek and dk are other bags of bits that are related and encode the actual maps efficiently.

So the trick is to make the mapping functions E and D both,

1, Scalable.
2, Efficient.
3, Provably linked.
4, Do not disclose the roots of trust.

Whilst the first two are relatively trivial, the second to are not as we are currently finding out.

No matter what way you do things at the bottom there are one or more bags of bits as “roots of trust” that have to remain secret.

But there is another problem which is how do you know,

1, The “creator” is who they say they are.
2, The roots of trust are theirs

Currently we do not know how to do the first, and the only way we know how to do the second reliably is via a secure communications “side channel” which is either an in person exchange or involves another set of “roots of trust” bags of bits.

So the whole thing basically rests on two things,

1, Secure side channels
2, Roots of trust

Both with their own set of secret bags of bits from top to bottom.

Clive Robinson • October 6, 2022 9:02 AM

@ Winter,

Re : Presentation of Evidence.

“Courts have handled this for millennia.”

It would be more correct to say that they have,

“Hand waved it away forever”

It’s realy only since the 1960’s that science has actualy got involved with the actual court process rather than just some small asspects of evidrnce testing by “hard science” (mostly used incorrectly, hence all the miscarriages of Justice bassed around “physical evidence” or it’s misrepresentation in courts).

Since then it has become more and more clear that it is amazingly easy to tamper with evidence of all kinds, often trivially so. Because the human mind is both extreamly limited and extreamly maliable and unreliable.

It’s known that ~1/4 of eye witnesses are compleatly wrong with what the actually observed within 10mins of the event. Likewise within 24hours ~1/3 of those remaining are wrong, or around ~1/2 change their recolections due to the way they are questioned. Thus for evidentiary purposes “eye witnesses” are giving factually incorrect evidence over half the time.

I had this nonsense pulled on me when I was a witness and I was shown a photocopy of a bank cheque and asked to verify “it was the cheque” by an obnoxious barrister… I badly upset both the three judges and barrister who was making such a rediculous request. Because as I firstly noted it was a photocopy not the actual cheque, so could easily be of a forgery, secondly I would have had no reason to memorise the unique identifing feature of the cheque number when I had seen the cheque originaly half a year before, and further that half the population who used shorter “credit card” and “phone numbers” every day that did not change could not remember them, worse around 15% of the population could not remember a four digit number after trying to deliberatley remember it, and I was not going to perjur myself… You could have heard a pin drop and the faces were a picture to see esprcially the barrister. I then said I can confirm that a cheque for that amount had been payed in by me into an escrow account I had set up for the purpose and that under the “bankers books/ledgers rules of evidence” they should ask the bank for a writen conformation of the cheque issuing branch, sort code, account number and individual cheque number, if it were important to the case, which it was not… The lead judge coughed looked at the other two who just looked blank then the barrister and asked if my answer had sufficed, to which he just noded then after prompting said “yes” (for the court records).

It is by the way, not the sort of thing you should do, because judges of all flavours do not like witnesses being anything other than dumb, so they can “handwave through paperwork of any kind as evidence” when it most clearly is nothing of the sort.

But it’s not just eye witnesses that are compleatly and utterly unreliable as evidence. But it has become court tradition to,

“Hand wave through any old nonsense paperwork as evidence.”

We know, not only is it the wrong thing to do beyond any doubt, but that we can improve upon it greatly. Worse we also know that the ability to fake evidence is way beyond the unassisted human to detect or even to suspect. You only have to see those old Russian photos where “heros that were now zeros” got removed to see how this has been true for better than a century.

Also remember, I have some experience in “debunking” forensics and bio-metrics and picking “unpickable locks”. The only bio-metric I did not come up with a work around for was retinal blood vessel mapping. The reason was not because I think it can not be done, I think it can, and for good reason, but I don’t want to hurt peoples visson by experimenting (technically your eye is as fragile as your brain and likewise the damage as unrecoverable).