An Open Source Mobile Phone Based on the ESP32 • Hacker News Board

Re: An Open Source Mobile Phone Based on the ESP32

#11

Post by distract8901 » Sat, Aug 26, 2023, 12:17 AM UTC

fsflover wrote: post #8

cri5ti wrote: post #7

Earlier quoted context omitted.

These open source / DIY mobile devices rely on an IC to perform the telephony side of things. In this example, a SIM800C made by SIMCom which could require additional "features" to pass certifications. How would you ensure there is no existing backdoor in the chip's firmware?

> How would you ensure there is no existing backdoor in the chip's firmware? What is the worst thing that backdoor could do?

Realistically, snoop on every byte passed between your phone's processor and the modem's chipset. Wort-worst case, injecting code into the phone's CPU through another backdoor or some other exploit.

Basically, taking complete control of the modem and potentially using that as a launch point for a more detailed attack.

Besides that, in the US at least, your phone's cell modem does have a backdoor. Every single one of them, no exceptions. Your telco can remotely update your modem's firmware and there is absolutely nothing you can do to stop it. Telcos are allowed/required to have total control of the firmware of any modem attached to their network. Source code is never, ever available. All cell modems are a total black box.

This also applies to terrestrial internet connections. Your cable modem or DSL has a firmware blob provided by your telco, no matter who you bought the modem from.

Re: An Open Source Mobile Phone Based on the ESP32

#12

Post by distract8901 » Sat, Aug 26, 2023, 12:22 AM UTC

cri5ti wrote: post #7

iAkashPaul wrote: post #4

Seeing the speed at which governments across the world are keen on breaking encryption or enabling backdoors, this appears to be one of the ways we're headed for.

These open source / DIY mobile devices rely on an IC to perform the telephony side of things. In this example, a SIM800C made by SIMCom which could require additional "features" to pass certifications. How would you ensure there is no existing backdoor in the chip's firmware?

> How would you ensure there is no existing backdoor in the chip's firmware?

Basically, you can't. See my other comment in this thread.

If your modem is used in the USA (and likely elsewhere), your cell service provider won't allow it on the network unless it's running firmware that they approve of. Period. This usually means firmware blobs provided by them with absolutely no means of inspecting what it does.

If it's on the network, it has a backdoor. No exceptions.

This is why there are no open source modems. It's not a legal possibility.

Re: An Open Source Mobile Phone Based on the ESP32

#13

Post by Gigachad » Sat, Aug 26, 2023, 6:05 AM UTC

oneepic wrote: post #9

iAkashPaul wrote: post #4

Seeing the speed at which governments across the world are keen on breaking encryption or enabling backdoors, this appears to be one of the ways we're headed for.

I guess one of the other ways is: "have a phone because it's required for website accounts and work -- don't do anything on it." Talk to your friends and family in person, which is _kinda_ arguably healthier. No social media, or hell, maybe not videogames either.

As everything becomes more and more spied on, this seems to be the way to go. I never say anything interesting to coworkers over MS Teams, I'll just wait till I see them in person before engaging in any real talk.

Re: An Open Source Mobile Phone Based on the ESP32

#14

Post by fsflover » Tue, Aug 29, 2023, 12:49 PM UTC

distract8901 wrote: post #11

fsflover wrote: post #8

Earlier quoted context omitted.

> How would you ensure there is no existing backdoor in the chip's firmware? What is the worst thing that backdoor could do?

Realistically, snoop on every byte passed between your phone's processor and the modem's chipset. Wort-worst case, injecting code into the phone's CPU through another backdoor or some other exploit. Basically, taking complete control of the modem and potentially using that as a launch point for a more detailed attack. Besides that, in the US at least, your phone's cell modem does have a backdoor. Every single one of…

Most of these attacks can be mitigated by having a modem separated by a well-documented interface and a kill switch. These are exactly what I have on my phone.