Immobilisers and (in)security

Barnaby Donohew asks if increasingly complex vehicle security systems are an opportunity or a risk

Published:  24 October, 2017

We need to talk about security. Why? Because deliberately or not, its effects are mutating our opportunities within the automotive aftermarket. We need to understand more about it and, at some point, to try to anticipate the eventual set of circumstances to which it might lead. As they say, forewarned is forearmed.

We’ll begin by looking at an example of a recent security system and checking out its inner workings. We’ll review its potential vulnerabilities and assess the need for, and impacts of, increased security. First though, we’ll cover some general concepts, to keep in our minds the bigger picture regarding possible motivations for increased security.


Security
Security is the protection of things having value, where they might be at risk from theft or attack; i.e. when they have, or are perceived to have a vulnerability. Security aims to prevent an agent of ill-intent (e.g. criminals, intruders, missiles, or computer-viruses etc.) from gaining access. The consequence of this is the introduction of barriers to those requiring legitimate access, such as owners, occupiers, citizens or data-holders. This dichotomy is at the heart of all security implementation issues. This always begs the question; what level of security balances an intended degree of protection from risk, with the subsequent barriers to legitimate access or freedoms?

As the assessment of risk primarily determines the necessary level of security, it is not hard to imagine that superficially legitimate security concerns can be used to justify limiting access to a favoured group. It’s a simple trick, just inflate the perceived risks and exaggerate the vulnerabilities where necessary. A similar mechanism can be used in a health and safety environment, where legitimate but undesirable behaviours in the eyes of the decision makers can be quashed by deliberate overstatement of the perceived risks. When loaded with the weight of moral absolutes (“lives are at stake”), the arguments seem powerful but are they really intended to shut-down reasoned debate regarding the actual risks? Anyway, the point is, we cannot have a reasonable discussion regarding proportionate levels of security without being able to properly assess potential vulnerabilities and associated risks.


Immobilisation
Vehicle immobiliser systems have been developed to protect vehicles from theft. There is a clear need for the security as the risks are very real. Car thefts were far more common prior to their development. Such systems work by only allowing vehicle mobilisation when a key, placed in the ignition switch, is from the unique set authorised to start the vehicle. The following describes a representative immobiliser system and its behaviour during ignition-on and engine-start conditions, just after the car has been unlocked. As we will be discussing potential vulnerabilities, the make and model is not given.

Component-wise, such systems usually consist of a transponder in the key head, a transponder coil around the ignition switch and an immobilisation control system within either a dedicated immobiliser control module, or another control unit, such as the central electronics module (CEM). The CEM might be hard-wired to an immobiliser indicator in the dashboard or instrument cluster (IC), to indicate the system’s status to the user. The CEM will communicate with the engine control module (ECM) using a CAN bus. Note that, if the CEM is on the medium-speed CAN bus and the ECM on the high-speed CAN bus, then a control module that is connected to both buses, such as the IC, will need to act as a gateway to communications between the two.

There are usually two stages to the authorisation/start process; the first, a key checking phase, is initiated when the key is placed in the ignition barrel and the second is a start-authorisation phase, instigated when the operator turns on the ignition.
A typical key checking phase might progress as follows (see Figure 1 for the representative signals): initially the system will be in an immobilised state, indicated by periodic flashing (e.g. once every two seconds) of the immobiliser indicator. When the key is placed in the ignition switch, the CEM energises the transponder coil (e.g. at 125 kHz), which excites the transponder. The transponder responds by transmitting identification and rolling code data to the CEM via an inductive voltage within the transponder coil circuit. The CEM will check the returned data against the stored data to confirm its identity. The CEM might double-check the key identity using the same mechanism.

The start-authorisation phase proceeds as follows: When the ignition key is turned to position II (ignition on), the ECM detects the ignition supply voltage and sends a start request CAN message to the CEM. If the key is valid, the CEM responds positively, with a code derived from the message contents sent by the ECM. In return, the ECM replies to confirm that the vehicle is in a mobilised state and that it can crank and run the engine. Upon receipt of this confirmation message, the CEM can illuminate the immobiliser indicator (e.g. with a one second confirmation flash) and then turn it off. If the key is invalid, the CEM will respond negatively to the ECM’s start request message, such that the ECM will not crank or start the engine, and the alarm indicator will continue to indicate an immobilised state.


Insecurity
The immobiliser’s subsystems could be vulnerable to several types of attack: Key recognition; The key recognition subsystem, consisting of the CEM, transponder coil or and transponder, could be prone to attack if the correct rolling codes could be transmitted in the right way and at the right time. Note that to move the vehicle, the correct mechanical key would need to be in place to remove steering locks etc. Key-less start systems present other sequencing issues (related to direct CAN messaging, described below), which would need to be co-ordinated with the press of the engine start button etc. The biggest vulnerability and simplest way to attack the system is to clone an authorised key.

Direct access to the CAN bus; If the start-request from the ECM and subsequent immobiliser related messages can be intercepted and the appropriate (algorithmically generated) response codes returned, then the CAN communication system could be used to carry out unauthorised mobilisation of a vehicle. The method would rely on a controllable communication device having a physical connection with the CAN bus. Timing is important (the messages are often expected to be received within a certain time frame) and the genuine responses that would be sent out by the immobiliser controller would need to be mitigated against (e.g. the filtering out of its likely negative response to a start request, that might cause the ECM to immobilise itself).

Aside from the practical connectivity and the sequencing issues, there is the issue of knowing how to generate the correct response codes to a start request. Although, the codes are observable in an unencrypted network, the relationship between the in and out codes can be extremely difficult to calculate using analytic methods alone and are more likely to be determined from reverse engineering of the control unit’s program files. Aside from the legal implications, the challenge is still great, which is very likely why it has not appeared to have happened.

Indirect access to the CAN bus; Given the potential difficulties of physically placing a communication device on the CAN bus, an alternative approach is to hijack a device that is already connected. Any internal (software or hardware) system within a connected control module that has access to the controller’s CAN interface might provide a channel through which unauthorised access could be attempted (especially if a vehicle manufacturer has already built-in a remote starting capability).

It is this type of attack that has been highlighted as a particular concern with the advent of connected vehicles, purportedly presenting hackers with opportunity to remotely control some or all of a vehicle’s functionality. There have been notably few examples of vehicles being hacked in this way and it will be very interesting to see if that changes over the coming years.
All in all, the challenges needing to be overcome to take advantage of any the three perceived vulnerabilities and to steal a car are great. Quite simply the easiest form of attack is to clone a key. The question is then, what are the motivations for ill-intentioned agents to attack our automobiles and are they likely to want to try to steal a car through attacking the immobiliser system? I’m not sure I’m qualified to answer that.


Information
There is a further, related, development that has already dawned within our automotive landscape. Our modern motor vehicles are capable of generating significant volumes of personal data regarding much of our travel and lifestyle habits. This information is hugely valuable. Google’s company worth is colossal and their value is driven purely by their knowledge of our online browsing habits (through the use of their web applications). For the most part, we are not always online. Imagine though, if they could collect a raw feed of data regarding our offline habits, such as those we might create when we travel within our vehicles. How much would the company that had access to that data be worth? With that thought, it is clear why tech firms are falling over themselves to tap into our automotive existences.

Given that all this valuable data is flying around unencrypted vehicle communication networks (much of it is required by engine, navigation, entertainment and ADAS systems etc.), why in their right minds, would the vehicle manufacturers not want to encrypt that data and keep it to themselves? By doing so they would be able to prevent any third parties, including (coincidentally) aftermarket diagnostic tool manufacturers, from having any access to a vehicle’s CAN bus data, without the vehicle manufacturer’s prior consent.

Now, in that context, wouldn’t it be convenient if the vehicle manufacturers jumped upon the reports of the hackers’ abilities to put lives at risk, so as to justify the encryption of vehicle networks? Conspiracy theory? Maybe. I am susceptible. I once imagined that the large discrepancy between real-world and quoted fuel efficiency figures could have been indicative of an OE-level distortion of engine test results…


Further tech info
http://automotiveanalytics.net/agile-diagnostics



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