Schneier on Security

Clive Robinson • October 13, 2012 4:03 AM

OFF Topic:

It would appear the “US China APT” mob are up to their usual political shananigens,

http://www.computerworld.com/s/article/9232180/Chinese_telecom_firms_pose_national_security_threat_US_committee_finds?source=CTWNLE_nlt_security_2012-10-09

Now let me be clear there is a lot of difference between taking sensible security measures and using faux security scares as a smoke screen for politicaly inspired protectionism.

The US made a political choice many years ago to let go of it’s US based secure fabrication plants etc and go do the COTS route to save a few dollars to look good come election time.

In the process they handed over much in the way of IP, skills, job security and National Security. They let the genie out of the bottle and in the process also opened a whole pandora’s box of problems. There is no excuse they were told very clearly that this would be the result.

Now the “Chinese War Hawks” and others are jumping on a political bandwagon, It’s not just the Chinese but any nation that produces base component parts that are a threat to US National Security, and at the end of the day “when the chips are down” on the work bench no matter where you got them from if there was no security custody chain from design to the bench you cannot implicitly trust the chips.

Thus you have two choices, the first is the hugely expensive set up US based secure fabrication again, or find some other technical way to mitigate the risk.

A politicaly inspired idea such as this one will not and cannot provide the security it claims to be for. Because at the end of the day supply chain security is horribly horribly complex and inordinatly difficult, thus it has more gaps and holes for individuals with ill intent to worm their way into than most could even. attempt to imagine.

I suspect if after rational non politicaly biased thought the proposed solution will involve a slow migration back to secure design and manufacture of chips and other key components and to use these in appropriate technical mitigation strategies for the bulk of components.

But it’s a big “IF” simply because there are to many rice bowls / pork barrels to be filled and there will be no change other than more political rhetoric.

In theory the US people will have a chance to make a choice on such matters fairly soon, but the reality is the Dog and Pony show of the Monkey in a Suit Pollitical process of “representative democracy” that most Western and other nations have will be compleatly subverted post election by the holders of the rice bowls and pork barrels who bought the “peoples representatives” a long long time ago from the previous fillings of their bowls and barrels.

Clive Robinson • October 14, 2012 5:12 AM

@ Vatos,

How much damage can an attacker do if you are no protected

It’s not a simple question to answer, and currently we are only at the begining of what people are thinking of doing with “Near Field Communications” which covers RFID and other “Contactless Technology”.

The first question to ask is what the technology actually does and how, as this puts a bound on what is practical to achieve using it. It is important to remember that the technology is agnostic, it is just a tool that like any other such as a knife and thus can be used for good or bad, and can thus also cause accidents.

Historicaly the technology started out to solve a simple problem of how to identify an object from something inside it as opossed to outside it. The reason for this is things on the outside are generaly the first to get damaged, obliterated, removed or changed. Thus by putting it in the object they make the identity much more secure.

Also the method chosen helps to prevent mis-identification of one object as another due to human transcribing error.

The original RFIDs where made by companies likes Dallas Semiconductors and consisted of a tiny silicon chip a capacitor and coil wrapped around it all sealed in a small package with some small enough and safe enough to go down a hypodermic needle and be embedded in live stock in areas they were not likely to enter the food chain. Each device supposadly had a unique serial number and would respond when energised by repeating the serial number over and over whilst it remained energised. Unfortunatly the number of bits asigned too the serial number was to few for serial numbers to be realy unique.

The purpose of the coil was to act as the secondary of a tuned transformer by which energy would be received from the primary coil in the scanning device and also provide the back path for the data that was the serial number. As such these devices generaly ran at very low frequencies and low data rates and had very short ranges of just a few inches and had no mechanism to deal with more than one device in the scanners “field”.

Various things were done to solve these issues including working with scanning frequencies upto the bottom of the UHF band, use of varying time delay before sending data and repeating it such that the multiple device in the scanners field issue was solved, and also modification of the way data was sent back to the scanner such that more data could be sent from the device.

However other uses for “contactless technology” became envisioned including programability and as such the chips have now become comparable in function to contact based Smart Card chips or SIMs you find in your mobile phone or credit card.
As such the use had changed from a pasive unidirectional data transmission of a serial number tag to one with bi-directional data communications and very large amounts of data that could be cryptographicaly protected, and used for carrying out financial transactions for such things as public transport fares.

But the development has not stopped there, others have realised that “Smart Devices” could actually act as many RFID devices and thus now mobile phones are getting the backend “Near Field” technology built in and can look like one of many RFID devices including all your credit and other payment cards, identity systems used to provide security in buildings etc as well as some proposed National Identity cards.

So in effect all of your financial and identity data including medical records etc will become put on these Near Field devices and as such stand as a witness for all your societal requirments. And when put on a smart phone the phone becomes for practical purposes you…

The reality is of course that any of these RFIDs can be cloned and thus are totaly reliant on other security measures such as PKI certs shared secrets etc all of which are known to be vulnerable in many ways as they are dependent on other security technology, likewise smartphones and other smart devices are known to be vulnerable because of their trust on other security technology.

In all cases this “other security technology” was designed with totaly different security goals in mind and thus can and is inappropriate for the new uses it is put to with the likes of RFIDs.

My solution to the problem is not to have RFID / Contactless / Near Field devices on my person. This already causes me problems as it effects my use of public transport. Currently in London you pay about twice as much for a bus ride if you pay by cash as you do if you use the insecure Oyster card, the alternative of paper based annual travel cards is being phased out fairly rapidly and cash payment is being made extreamly difficult with ticket offices being run on reduced hours or closed entirely. Some banks are including Near Field Technology in existing contact based credit cards, from what has been said it appears you will have to move banks if you want to opt out, which as it’s an Industry drive just as was Chip-n-Pin you won’t be able to do fairly quickly.

Now when you add the mismatched security aims of the base systems to that of the financial systems overlaid ontop of them you are going to have more security holes than a second hand pair of string underpants and a consiquent loss of support from those who sold you the systems (ie they will as with Chip-n-Pin Externalise the risk back onto the “customer”). And with potentialy large amounts of money to be made you can guaranty that Organised Crime are going to get involved just as we currently see with OnLine Banking.

So as all these Near Field Contactless RFID systems can be made to work at considerably more than arms length you have to ask how long before you get “walk by contactless mugging”?

Such crime will become a numbers game just as it is with ATM skiming of peoples current bank cards. If you are in a high risk area you need to take more precautions than in a low risk area to have the same level of risk. But the risk is always there as long as society pushes you to use the technology and opting out is not possible. The more precautions that people take or the easier it is to use the attacking technology the more wide spread the crime will be. Thus sensible people will use whatever precautions they can and if they work RF shielding wallets will become a sensible precaution.

However they have downsides both personal and societal.

On the personal side you have the conveniance or more correctly the inconveniance factor to consider. In London we have the Oyster contactless card for buying bus / train / underground / over ground / tram and other public transport services. Standing on a bus near the card reader you can observe peoples habbits, it’s got to the point where women press quite sizable handbags up against the reader rather than get the card out. In many cases the time it takes them is longer than it would takee them to pull it out of a pocket and put it back again. You also see people holding their purses and wallets up to the reader and it failing because they either have two Oyster cards or they also have one or more of the newer bank cards with near field contactless technology built in. Basicaly two or more near field cards confuse the readers that are not that reliable anyway which is why quite a few people have two oyster cards…

Think about how the conveniance / inconveniance of an RFID proof wallet would effect you?

However you may not get the choice because of society aka the Gubbymint and it’s money grabbing ways to pay the voter bribes that get them elected to their personal grave trains.

The very proflagate previous UK Government (many of them caught for illegal activities involving money) wanted compulsory ID cards with Near Field Comms in and heavy fines for not carrying them on you at all times.

It is an idea that is not going to go away as the tax take from big businesses carries on dropping in various ways (google HMRC and “Dave Hartnel” and the outrageous sums he alowed various big businesses such as Vodafone Tescos and a couple of hundred other major companies to avoid over a good dinner and a handshake). So we are moving from a tax on business based government revenue system to a “personal tax and fine” revenue system.

Some years ago I predicted that in the UK what we would have is a “big brother” style system where there would be random mandatory checking of ID and on the spot fines for not carrying ID… Well we’ve started well in on that path by “conditioning the plebs”.

In East London the Border and Imigration people are already running random (usually racialy profiled) spot checks at public transport hubs like Stratford to look for illegal immigrants. Even when those members of the racialy profield group do carry their ID they are often detained for lengthy periods of time whilst they are “cross checked” which causes them problems with their employers for being late to work etc. We also have due to the “war on terror”, “Get tough on knife crime” and a whole host of other initiatives various LEAs setting up random walk through metal detectors and stop and search initiatives.

Think how easy it would be to add an extra detector in the “walk through” for your National ID card, if it’s not detected you get pulled to one side and seriously inconvenianced to show it or be fined a substantial amount…

As such RFID proof wallets would slow such a cash cow system down and raise costs initialy you would be very servealy hassled and humiliated (TSA style) because “you obviously have something to hide” then if sufficient people did it the wallets would become a prohibited item subject to yet another fine etc… Oh and to ensure that it works they way it should each person on the walk through team will be on a bonus scheme bassed on how many people they catch, not just for ID card fines but all sorts of other finable offenses as well…

Such is the society we are having forced on us by the Politico’s and their Big Business pay masters.

Clive Robinson • October 14, 2012 10:25 AM

@ Vatos,

Am I correct in saying that if someone uses a scanner near my contactless bank card, they then have enough information to perform a fraudulent transaction?

It depends on a number of things, firstly if it is an ordinary “radio scanner” as used by “Hams” it is only capable of picking up the field generated by the contactles card if it is activly being used within the range of it’s antenna system. Further the data should be multi level requiring knowledge of not just the protocols in use but any encryption as well.

Thus even if an attacker has access to the same hardware that is used in a shop EPOS terminal it may well be incapable of initiating any kind of transaction beyond the very basic levels.

That said fialings in the systems may well make PK Certs and shared secrets vulnerable in all sorts of ways. You only need to see the issues arising from Chip-n-Pin to realise just how difficult a process it is to secure financial systems. Further some of the near field systems used for paying for public transport have had their secret keys and shared secrets found by researchers, which means it is very likely organised crime is also more than aware of these secrets.

The problem is neither you or the system designers and implementors can prove these systems are in any way secure (you cannot prove a negative any way). So a wise person, to limit their risk proffile must assume they are not secure in any way, and that it is simply a numbers game that they cannot win at. The best they can hope for is to draw before their number comes up and they lose, unless they take further action such as ‘not playing the game’ or ‘moving the goal posts’.

As I noted earlier “society” will not let you be a member and not play the game, so you have to look at how to “move the goal posts” for your own protection.

One way to do this is to only ever use a debit card attached to an acccount that you keep virtualy empty. That is you plan ahead and only transfer money into the account shortly before you make a purchase. However you need to use a process that is in turn not liable to attack so don’t use online banking. This can be done because some banks alow you to make transfers from an ATM machine but only to pre-aranged accounts. Providing the account with the debit card is with one bank and the ATM transfer account is with a different bank then the level of work done by an attacker has vastly increased. You can further back stop this in other ways, the important thing is not to have any credit or overdraft facilities in any of the back stopped accounts involved. Thus the worse loss if you do get attacked is the small amount of money in the accounts at the time and any bank charges run up by the attackers that you should be able to get back in most juresdictions from the banks.

As an individual or organisation you realy should not have to do such things, however because many of the banks have poor security and protect themselves by externalising the risk onto their customers in many juresdicitons you have to think creativly to protect yourself.

Clive Robinson • October 19, 2012 11:51 PM

@ RobertT, Nick P,

… the hacker will have physical access to the device so they can easily fiddle with the Power Supply to create nonstandard start-up sequences which do not properly trigger the Reset circuit. Typically tricks involve using non-monotonic supply ramps…

And before the hacker was the low cost battery charger…

I kid you not, I used to be involved with FMCE design for the likes of cordless and mobile phones and looked into issues with electronic wallets and pocket gambaling machines going back into the 1980’s.

One persistant problem was lockup or eratic behaviour caused by the rechargable (NiCad) batteries and the 10cent or less charger circuits. In the hand held device to save cost there was no power switch that is the battery was always connected to the electronics…

Essentialy what happens (and it’s difficult to reproduce reliably) is that the charge circuit is effectivly currentl limited and the very nonlinear load of the discharged (but not compleatly) battery and the CPU trying to reset pulls the charger into currentl limiting and “wierd Sh1t” (Trade mark claimed for 😉 starts happening.

What is happening is aproximatly as follows,

The battery is at some low voltage Y that is bellow the threshold Z that the CPU will work reliably but not below the CPU off voltage of X. Although the difference between X and Z is small at some point the battery will be in the gap. CPU manufactures like Motorola put circuits into their CPU chips to try and detect the condition and prevent it, they also try to arange that the reset cascade happens in a certain sequence to stop excessive current being drawn. What the chip makers cannot do is use “time” for the sequencing as there will always be a slower rise time, thus they often use voltage which is also problematic. What their designers did not expect was for the slowly rising voltage to dip again, and this happens due to the current limit effect and the increasse in load as the CPU cycles up…

The obvious solution is put the physical switch back but this has it’s own problems which was why it was removed in the first place. So the next best solution is an “electronic switch” but… they have their own problems as well when you are designing them with descreate transistors and resistors etc. Not the least of which is all the designs people had come up with had very poor and unreliable switching charecteristics due to getting the series pass element to switch. In effect they were all linear high gain amps using multiple transistors (expensive) which also sucked almost as much current from the battery as the CPU in standby mode cutting the standby time by nearly 70%.

The solution I came up with back then used just two transistors the series pass “switching” element (PNP) and the detector/driver (NPN) the trick was to make the detector/driver a current biased circuit using two resistors one from before the series pass element and one from after the series pass element thus using the start of the turn on of the series pass element to significantly increase the current bias to the base of the driver transistor. The detector was in effect the base bias turn on voltage of the transistor (aprox 0.7V) which although temperature sensitive was sufficiently reliable. The two currents also ment importantly that unlike the other linear amp designs the circuit had hysteresis so the turn on voltage could be set well above CPU voltage Z and the turn off just above the CPU turn off voltage X so the CPU did not see a reversing voltage in the gap. Further it also alowed the turn on voltage to be set such that the battery was sufficiently charged so that it would be able to handel the current rush of the CPU turn on without it’s voltage dipping back below Z. Although I urged the company to pattent the idea they decided not to… Any way the UK arm of the company is now long gone because it never went out to get pattents to protect it’s IP because it thought the process to slow and to costly…

All that aside as you note there is a choice between a fully determanistic CS-PRNG and one which is augmented by a TRNG as a TRNG on it’s own is way way to far from being sufficient in it’s own right even for low security applications. At the end of the day it is very much down to how you chose to do things based on the application involved and the “real estate” costs in the design. In the likes of electronic wallets and pocket gambling machines you have no choice but to use real entropy somewhere in the system, and importantly it has to be somewhere fundemental and inherantly not “get atable” without being atleast tamper evident if not preferably destroying the device entirely.

Where you are not dealing with attackers with direct physical access and you are not working at the chip level you have to consider “supply chain poisoning” etc where you cannot trust the components to be what they say they are in the data sheet and on the package. And this is probably not be with the intent by covert foreign Gov operatives of owning a down stream system at some point in the future. No it’s much more likely to be “Chinese Knock Offs” or stolen “out of spec” parts or even low spec parts relabled as high spec parts carried out by organised crime.

The result of these faux parts is in most cases the internal function is broadly the same just not to spec in ways you can easily measure from the device pins. Unfortunatly TRNG’s for the most part work at the edges where “out of spec” most often happens. Which is why from a COTS system developers point of view avoiding TRNG’s is advisable as it’s less costly than mittigating them

I like your idea of using a ADC as a seeded TRNG however I will need time to mull it over. One thing I would note however is your seeding LFSR should realy have a nonlinear output that drives the ADC to make the attacks harder. As a quick “off the top of my head thought”, you should be able to get a realistic nonlinear circuit using an AND and OR gate array with little difficulty and not much real estate. And you could always gate paths through the array or simpler add a little “whitening” at the array input with XOR gates and “PUFs” to make it more unique to each actuall chip.

The joys of COTS system design as opposed to chip design is you are always “piggy in the middle” and avoidance or mittigation of your suspect component parts is all you can do. The former is generaly reliable in outcome the latter definatly a “cross your fingers and hope” stratagie.

However it’s getting to the point now with SOC that avoidance is just not cost effective in an ever increasing set of cases and mittigation unavoidable even though it’s costly and unreliable unless done with extream care.

As I’ve indicated in the past “Prisons-v-Castles” is a mitigation stratagie of parts of unknown provinence that could be suspect in many ways. Unfortunatly TRNGs by the very definition of their function are very difficult to mitigate if not impossible when it’s possible to hide in the grass of the statistical tests…

Clive Robinson • October 21, 2012 1:48 AM

@ RobertT,

I’m not a believer in “full disclosure” of security related circuits / systems

It is another one of those philosophical questions 🙂

Back in the days of code books and mechanical cipher machines and simple ciphers that could be memorised and carried out with pencil and paper a Proffessor of Languages in a select Paris accademic institution thought the problem with obscurity in largely deployed systems used by the Diplomatic and Military services was insoluble. So Auguste Kerckhoffs came up with a series of principles that still carry his name which were published in 1883 [1]. A lifetime later a mathematically inclined individual who would become one of the founders of information theory Claude Shannon re-expressed one of Kerckhoffs Principles as “The Enemy Knows the System”.

Which gives rise to the question have we advanced sufficiently in our understanding and science to make obscurity / obsfication sufficient such that the enemy does not know the system?

Hmm two deeply philosophical security questions in one thread… I guess @ Nick P will be bookmarking this page 😉

Your comment suggests that you think in certain areas, security by obscurity is worth while if not valid in mass produced items. And my personal guess is it’s again an open question in certain respects.

My guess is based on the following thought chain,

1, We know all security is a tool.
2, We know all tools are agnostic and can be used both in defence and offence.
3, We further know that in the main defence against offence relies on Information or Mitigation.
4, We also know that broad mitigation can work against attacks we have know knowledge of thus we don’t need to know all information [2].

Therefor it’s sensible to mitigate by obscurity specific details as even though it may not stop an attack it will raise the thersholds of ability and time against potential attackers. It also helps reduce the oportunity of others to turn the tool on you which is a viewpoint taken by most major Governments and their security organisations and in certain respects used as a double bluff in the likes of the Haglin coin counting mechanism used in some US field cipher machines.

But in recent times it would appear that the US and other Mil organisations realise that the boot can be firmly on the other foot with obscurity being most definatly out of sight. And thus recent behaviour by the US Mil on funding to finding supply chain poisoning appears to confirm we are not alone in that thought that in certain places and certain ways obscurity can be good security.

[1] See David Khan’s book Codebreakers.

[2] We saw this point in practice in the 9/11 attacks where a fire/safety officer in one company had made sure that the employees all knew the fire evacuation proceadure and had often practiced it. The result was a much greater percentage of that organisations staff survived compared to other less well prepared organisations in similar positions. There is little or no chance he would have considered a plane flying into the building as part of the evacuation training [3]

[3] The 9/11 attacks were not the first time NY had had a plane fly into the side of a skyscraper. Back in WWII at 9:49 on Sat 28th July 1945 a ten tonne B52 bomber piloted by Lt. Col. Bill Smith in low visability conditions missed several skyscrapers before it did fly into the side of the Empire State Building. But compared to 9/11 it actually caused minor damage, of a 18 by 20 foot hole on the 79th floor, killing the three crewmen, 11 office workers and injuring 26 others, with repair costs estimated at around 1million USD.

Clive Robinson • October 22, 2012 7:34 AM

On obsfication & randomness.

For a moment flip your thinking the other way up and instead of thinging “information” is an artifact of our “physical universe” ask yourself what the implication of our “physical universe” being an artifact of an “information universe”?

It is very easy to realise that there is more information in the universe than there is physical matter, that is information can be encoded not just on the state of the most fundamental particles it can also be encoded by the relationship of particles to each other and other encodings as well (what I call data shadows).

The problem with information encoded by relationships is two fold, firstly like a one time pad you need to know the key to reveal the information, secondly you need to be able to store and communicate the encoded information and the key to also be able to store and communicate thus recover usably the information…

Thus we know from this that it is not possible to know all the information there is to be known…

Therefor we know we will not always be able to determine information because even our physical universe obsficates it from us.

Now if we assume our physical universe is a subset of an information universe (which is what it appears it might be) we need to ask questions about information, but can we actually get meaningfull answers?

Possibly not, look at it this way unstable atoms break down to other atoms that may or may not be stable untill you get down to the bottom of the curve where the atoms are stable. The thing is the process is both apparently random on which individual atom breaks and when but seen overall is very predictable in terms of a half life even in quite small quantities. Ask yourself how do reconcile this in reality (not statisticaly), that is how does an individual atom know it’s time for it to break to maintain the half life curve?

Then look at all our other “random processes” which in reality when they are below a certain scale are not realy independent of each other, because on mass their behaviour is predictable statisticaly.

You could argue that on a higher level than the physical universe we perceive there is actually a determanistic process we cannot see going on, and on the levels we can see on an individual basis of the minimum quantity of matter or energy a process that looks random put on mass determanistic.

Our definitions of random are manyfold but at the end of the day they come down to “unpredictability” which as far as we can see means not “nondetermanistic” only “we cannot see the determanistic process” thus it is hidden or obsficated from us.

So as for the “mathematically inclined (Academic) Crypto types that have bad mouthed obscurity just to sell their own brand of snake oil” they know (One Time Pad) obscurity is actually the bench mark against which their determanistic models are measured.

But obscurity has just like the one time pad to be bounded in it’s use otherwise determanism shows through. In the case of the OTP use the same key twice and you can cancel the random noise out to leave the addition of two determanistic but unknown sequences (plaintexts) which can usually be seperated from each other.

For instance if you take several plain texts and add them together (mod 2 etc) at some point their determanistic charecteristics will be nolonger determinable from an unknown or random sequence (at one point it was belived that a book code using four books was from a practical viewpoint unbreakable).

And it is this “add independent determanistic effects” to get “random effects” which is where obsscurity does work. That is you can raise the bar to the point where our current mathmatical tools cannot tell the diference. In this respect it is a form of “defense in depth”.

But… tools are methods and we know at the end of the day methods like wine generaly get better with time.

This is something we see with block crypto with the safety margin of extra Fiestel rounds.

So I don’t think at heart cryptographers are trying to sell snake oil, but ONLY “mathmaticaly valid methods”. It’s the next step to practical implementation where it all goes wrong and “side channels” especialy timing side channels open up because they were not considered as part of the idealised / clean mathmatical model.

Now I know one reason why this happens and it’s the perenial war of “security -v- efficiency” whilst it is possible to have special purpose dedicated systems that are both secure and efficient they are of no use for other things. General purpose systems are neither inherantly efficient or secure but are of use for many things.

It’s squaring this circle between specialised and general purpose that is extreamly difficult. An unoptomised CPU design is actually easier to write secure code for than an optomised CPU design, it is the optomisation to improve efficiency in certain operations that opens up the side channels. If and only if you are aware of exactly how these optomisations work can you mitigate their effects and have a secure design.

I very firmly point the finger at the NSA for the problems we have seen with timing channels in practical AES implementations. Why. Because they would have known without doubt about “security -v- efficiency” and as NIST’s domain experts they should have included this in the AES competition specs. The fact they did not can only be seen as a fairly deliberate “oversight”. When you add in the deliberate requirment for speed/efficiency into the competition with the requirment that this “speed freak” software be made available to all it was inevitable that nearly all initial AES implementations would be riddled with timing channel issues.

The question is why did the entrants not raise this with NIST it is clear that some of the other entrants have higher immunity to side channels than novel “bricklayer design” of Rinjdael.

It is in effect a higher than “specification level” subversion attack and as such you have to wonder who thought it up.

Although we are not stuck with AES NIST never put into consideration a mitigation policy of what to do when (not if) AES defficiencies come up. For sometime now I’ve advocated for flexible and extensible framework standards that allow for the changing of not just the primatives such as AES but the modes they can be used in as well but further what you might call the Meta-Modes which are in effect the practical realisations of the way we implement crypto in applications. For instance a PRBS to generate a nonce is defined by the size of the output and the seed values, the fact it could be done with either a stream or block cipher is fairly irrelevant to it’s function, likewise if it was a block cipher it’s mode be it CTR or a block feedback mode with or without IV/whitening is again irrelevant to the overall function, likewise if the block cipher is AES/blowfish/etc.

One of the things about the latest competition for hashes is that again the “novelty act” appears to have been selected, giving rise to the thought about what practical implementation issues such as timing side channels are we going to see with it down the line…