Schneier on Security

Clive Robinson • October 26, 2017 11:12 AM

@ Gweihir,

The whole stance by publishers is so anti-fact and anti-rationality, it is staggering.

It’s actually “anti-reality” which is darn dangerous at the best of times, and this most definitely is not the best of times.

Back in the mid to late 1990’s those who had (mis)appropriated intellectual property by various means usually foul not fair, were sold a dream of “total control”.

The main idea back then was “Digital Watermarking” (DW) and chips in consumer devices. DW was based on the ideas of Low Probability of Intercept (LPI) Direct Sequence Spread Spectrum (DSSS). How ever whilst the radio spectrum is not subject to arbitary stretching and compressing digital data can be easily modified that way. The result was that Ross J. Anderson and students at Cambridge Uni Computer Lab did two dimentional manipulation that destroyed the DW signal without making realy human perceptable changes. That killed of that DRM idea at the turn of the century.

The point was that the IP rent seekers finally realised that Digital Data was a problem they tried a form of proprietary encryption on DVDs called the Content Scrambling System (CSS) but as it had to run in software as well as hardware, the way it worked became public knowledge and the resilt was an application for *nix called De-CSS that as the name suggests got rid of the DRM.

The response of the rent seakers was to bribe politicos and get the Digital Millennium Copyright Act passed thst has way to wide a scope and way to huge penalties, as well ad stiffling “free speech”.

But this was still not enough earlier attempts at forcing DRM chips in consumer devices like the so called “Fritz Chip” had failed due to counter lobbying and quite nasty rhetoric from some quaters (nothing compared to the fractious legal action by the “rent seekers” enforcment associations but still not civilized).

So the rent seakers decided to go a different route for their desired extraction of unentitled income. Long story short computers got the Trusted Platform Managment (TPM) chips. These were sold on the notion they were a user side security device to stop malware which Microsoft pushed rather than actualy write a secure OS and apps. As can currently be seen that ruse has had little or no effect on malware infection so was a compleat lie from that point of view. However it gives Microsoft and it’s chosen few the ability to wield immense power over users. However it is by no means certain that TPM is actually secure, it’s hierarchical in it’s trust levels, which means that the chip manufactures could put in a hidden master key that would make the sort of backdoor the SigInt agencies would quite literally “kill for”.

But the thing is like most DRM TPM is the equivalent of “off line” operating. With a little thinking it can be seen that even if you can not get at the keys in the chips there are ways of getting at the unprotected data.

To see why think about how “signed code” is both loaded and checked. The checking of the signing only happens when loading, which means that if you can modify the code memory after the code is loaded it will still function. There are various ways this can be done including halting the CPU tristating the busses and directly reading to the memory via the busses. The only way to stop that kind of attack is by using software that is encrypted in memory. Whilst this is done on some microcontrolers it does take up a lot of resources, and is not currently something you would use in high performance systems due nit just to the CPU / CoPro overhead but also due to the significant extra increase in delay on memory transfers.

But then even encrypted memory microcontrolers have found to be wanting in various ways in the past, as getting it right can be difficult at best.

The result is off line DRM is at best a deterrent not a serious security hurdle. Whilst this might change in the future, it’s not a high priority for CPU manufacturers who can find better things to do with the silicon real estate than generate lots of problematic heat and burn battery life at twice the rate. Which also in effect kills their specs which marketing at least would see as a major product killer.

DRM unfortunatly will always be around, because the greed of the rent seekers means they will pay and pay for such systems, but at the end of the day they will get little or no benifit at best and as you point out probably lost sales as well. One day they might wake up and realise they are buying very expensive snake oil and not getting any return on it, but they are blinkered by the dreams of power over people, so I for one am not holding my breath on them wising up.