From Silicon Labs: "Upgradeable Security is Not Optional for the IoT"

We have yet to see the full-fledged economic value of billions of new IoT devices entering multiple industries, though we can prepare ourselves with what we know will come along with it. As with any new innovation and/or market, malicious adversaries and attackers will lurk and invade for their own piece of the pie. 

Despite the looming security threats, companies and developers designing new IoT products often like to focus their attention on the application itself versus proper security. Security slows the time-to-market and is often viewed as inconvenient because it increases cost.

But no one wants to design an application that’s prone to hacking or data theft. Undesirable events like high-profile hacks can lead to serious brand damage and loss of customer trust, and worst-case is a slow down or permanent reduction in the adoption of IoT.

When it comes to security, IoT is no different than previous technology innovations such as PCs, smartphones, and the Internet itself. If security is not addressed sufficiently by the creators of the technology – in this case, IoT product designers - the oversight could have devastating effects on the entire market, and it will no doubt have negative consequences for the individual companies opting to design irresponsibly.

Varying Degrees of Security

To avoid these scenarios, designers need to change how they view IoT security. Unfortunately, it’s not as simple as a “to have or not to have” decision. Security is not binary. The reality is there are many different levels of security. A device can only be considered secure in the context of an attacker, when the level of security is higher than the capabilities of the attacker.

Moreover, the capabilities of the attacker are typically non-static, and therefore, the security level will change over time. The improved capabilities of the attacker can come about in several different ways, from the discovery and/or publication of issues and vulnerabilities to broader availability of equipment and tools.

History has taught us some valuable lessons about how fast security threats can change for an object. A typical lifetime of an IoT-device depends on the application, but in industrial applications, 20 years is a common timeframe. A device launched in 1998, for example, was once only vulnerable to nation-state attacks; today it must be able to withstand DPA attacks by hobbyists with $300 for tools, some spare time and lots of coffee. Predicting the future capabilities of a class of adversaries is very difficult if not impossible, especially over a 20-year timespan. How does the adversary look in 2040? One might speculate if it is even human?

Bootloader Benefits

The only reasonable way to counter future attack scenarios is for the security of the device to evolve with the increased capabilities of the adversary. This requires IoT security with upgradable software.

Of course, there is functionality requiring hardware primitives, which cannot be retrofitted via software updates. However, it is incredible what can be solved in software when the alternative is a truck-roll. Though, it impossible to predict and account for all future attacks.

Secure updates involve authenticating, integrity checking, and potentially encrypting the software for the device. The software handling such security updates is the bootloader, typically referred to as a secure bootloader. The secure bootloader itself, along with its corresponding cryptographic keys, constitutes the root-of-trust in the system and needs to have the highest level of security. A secure bootloader is functionality IoT vendors should expect to get from the IC manufacturers.

The authentication and integrity check should be implemented using asymmetric cryptography, with only public keys in the device. This way, it is not necessary to protect the signature-checking key in the devices. Since protecting keys in deployed devices is (or at least should be) harder than protecting keys in control of the device owner, it is also acceptable to use the same bootloader keys for many devices.

Encrypting the Software

Encrypting the software running on the IoT device has two benefits. First, it protects what vendors consider to be intellectual property (IP) from both competitors and counterfeiting. Secondly, encryption makes it more difficult for adversaries to analyze the software for vulnerabilities. Encrypting the new software for secure boot does; however, involve secret keys in the device, and protecting secret keys inside a device in the field is becoming increasingly harder. At the same time, newer devices have increased resistance to DPA attacks. Furthermore, a common countermeasure against DPA attacks is limiting the number of cryptographic operations that can take place to make it infeasible to get sufficient data to leak the key. Even though protecting the key is difficult and motivated adversaries will likely extract it, key protection makes attacking more difficult for the attacker.

Another consequence of secure updates is the likely future need for more memory in the IoT device. This is a complicated trade-off for several reasons. First, software tends to expand to the memory available in the device. So, a larger memory device requires discipline from the software team to leave room for future updates. The other complication is the value of free memory in the future versus the device’s initial cost. More memory tends to increase the cost of the device. This cost must be justified both from the device maker and the consumer point of view.

Finally, it is important to have a plan for distributing the security updates. For most devices, these updates use the device’s existing Internet connection. But in some cases, this requires adding or using physical interfaces such as USB drives (i.e., sneakernet). It is also important to consider that the devices might be behind firewalls or in some cases disconnected from the Internet.

IoT device software is often fully owned and managed by the device maker, meaning the device maker should have proven processes in place to internally protect the signing keys and particularly those who can issue updates.

Securing the Future

There is no such as thing as a 100 percent secure-proof device, especially during the entire duration of a product’s lifecycle.

Yet it is possible to understand and prepare for the most likely threats and safeguard for future threats by designing in the ability for upgradable software updates. IoT developers must adopt themselves to this critical mindset of responsible security design. Otherwise, they are placing their innovations, and IoT’s market potential, into the hands of adversaries.

For more on upgradeable security, Silicon Labs’ senior director of product security Lars Lydersen will be hosting a webinar in which he'll provide the insight and background to help in evaluating what security functionality is necessary in an IoT design.

Source: https://www.silabs.com/community/blog.entry.html/2018/05/01/upgradable_security-vY62