Is a 'dumbphone' mobile more secure for basic phone calls than a smartphone?

Question

By dumbphone I mean: no internet connection, very limited features, etc.

By more secure I mean: secure from malicious and direct hacking. I don't mean as in protected from government tapping/snooping; I don't mean from authorities who could be granted access somehow, through the mobile operator company.

Has the security of the basic phone call changed much, in the last 10 years ? Obviously smartphones have an endless number of new security holes as time goes on, a quick browse of Apple's security updates history, or searching Android in the tech news, proves this. But I'd suspect most of these vulnerabilities can be utilised because of the frequent connections to the internet made with them. So, do smartphones utilise anything new [purely in] the initiation and connection of just the phone call itself ?

Answer 1

Has the security of the basic phone call changed much, in the last 10 years ?

So, do smartphones utilise anything new [purely in] the initiation and connection of just the phone call itself ?

Yes. There are new technologies used to establish phone calls in cellular networks. Those new technologies mitigate some attacks which were possible due to flaws in the older ones. So if you use a "dumbphone" that runs on the older technologies you are subject to those attacks (i.e. the inverse is true, the smartphone is in this respect more secure).

The technologies used in the cellular networks basically evolved over time like this: 1st generation (analogue), 2nd generation (GSM etc.), 3rd generation (UMTS etc.), 4th generation (LTE etc.).

If you use a device running for example the GSM technology, an attacker might intercept your calls with hardware costs of only about $30 USD. Intercepting calls made with the newer technologies is harder up to a point where only nation state attackers can perform them.

Answer 2

Case in point: Snowden uses a feature phone (i.e. 'dumb phone). A few people would like to attack his phone, but even if they succeed, it's a very limited reward. OpenMOKO is an example of such a phone. An attacker will likely need a good working knowledge of the system he is trying to penetrate, and android is easy to persist on once in. Harder to persist on a classic Nokia.

With a HackRF One and OpenBTS it is still possible to IMSI catch (and downgrade crypto, and listen in on protocol data + calls), and in any case it is my understanding that when the phone modem is using DMA you are somewhat at the mercy of your telephony provider - who can silently push configs, over-the-air updates etc.

If possible, ensure that your phone cannot have its 4/3G downgraded to broken GSM. If using a smartphone, do not use default browsers, use apps that provide end-to-end crypto for IM and calls (WhatsApp, Wire, Signal (the last one is best), and if necessary VPN on public wifi.

Answer 3

Sure, Internet connection and physical data intefaces like USB or microSD constitute attack vectors.

However, if you use your smartphone as a dumbphone (i.e. never enable data connections, never plug an SD card in it and never connect it to devices other than the official charger), the level of risk is nearly the same.

It can be argued that if your phone falls in the wrong hands, nothing will prevent the attacker from using those interfaces, or exploit Android bugs. But physical access is fatal for dumbphone security as well. Those devices also have debug interfaces and interface bugs which can be exploited.

Answer 4

I think you might be conflating two different things when you say "more secure".

On the one hand, I'm sure that the old proprietary operating systems of 'dumb phones' could easily be hacked if the attacker could analyze the firmware, versus 'smart phones' where security, permissions and the safety of managed code prevent a lot. From that perspective 'smart phones' are vastly more secure.

However, if you look at the two phone types in terms of attack surface, there are vastly many more ways of attacking a 'smart phone' than a 'dumb phone'. If all your 'dumb phone' can do is text/call, the hacker is limited to physical access or cellular MitM attacks. Bring Bluetooth or internet connectivity into the picture and you open a couple more avenues. But on 'smart phones', someone could convince you to download a malicious app, or they could attack you through a legitimate app that has vulnerabilities, or they could phish you, etc.

However, if you had both a 'dumb phone' and a 'smart phone', and limited your activity ONLY to phone calls, I would still expect the 'smart phone' to be more secure with respect to targeted hacking.

Answer 5

It can mitigate some risks but expose you to some other ones.

You see, in most smartphones (but not all), the cellular network interface is separate from the main CPU and only talks to it through a specific bus - if the mobile interface is compromised it's not game over just yet as the attacker still has to compromise the main CPU (though vulnerabilities in the code that controls the mobile interface, text message parsing like Stagefright, etc).

Feature phones, on ther other hand use an all-in-one chipset that runs both the OS as well as handle cellular communication. If that one is compromised the attacker gets full control of the phone straight away. It is also much easier to hide malware in a feature phone than a smartphone because you don't have to worry about future OS updates breaking it, or some advanced features like a Terminal (on Android and jailbroken iOS) which could allow someone knowledgeable to detect your malware.