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Comment by semi-extrinsic | Hacker News Reader

No disrespect to Snowden and Bunnie, but it seems to me that a much simpler solution giving you a much higher OPSEC is to buy a smartphone with a removable battery. No battery, no radios are on.

And if you are truly paranoid, it's simple to disassemble the phone and look for/remove any backup batteries. I know, I had to pull the backup battery from my wife's Moto G after it fell in the sink.

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Wouldn't it be easier to use some kind of case or pocket [0] that acts as a Faraday cage?

0: http://www.popsci.com/sites/popsci.com/files/styles/large_1x...

That seems safer, with Snowden's device it has to detect transmission after it begins to occur in order to trigger shutdown or alert the user, so it's going to leak some amount of RF even if little. A properly constructed Faraday cage shouldn't though.

I think that Snowden's device would play a different role, I was comparing it to removing the main and backup batteries.

So it records and transmits later, at opportunity.

Good point. I guess it depends on the use case.

+1. If you are trying to detect surveillance by considering RF emissions but only some of the time, a sane attacker will simply have the bug record what it needs and transmit it in a burst later when you will not find RF activity suspicious.

You need to prevent the thing from recording you in the first place.

A metal case will block any unwanted RF emission. That said, the article states that the goal is to make it possible for users to still use their smartphones as camera, GPS, or whatever tool you need on it, while being safe.

As someone who knows a bit about computer security I find it mindblowing that journalists would go into war zones and expect to be stealthy with their smartphones in their pockets but they apparently are willing to risk their lives for their iPhones, so the best we can do is offer tools to mitigate the risks.

Snowden explained that the CMOS button battery is enough to send a transponder signal that can be heard by a drone. He said the only way to shut it down is to put it in a freezer.

I mean, I'm a programmer, I am not an expert on sigint stuff, but I don't think it's very hard to innovate in intelligence gathering technologies.

No battery leads to a useless mobile computer.

Depends on your use-case. If you only want to stop communications during a specified period of time (e.g.) during a "secret" conversation, then this is useful. If you have any apps installed that might be polling the 'net for information (e.g. checking the weather), then this is useless in the general case of "the phone is on my desk next to me while I'm working."

What is described in the article does not do traffic inspection, it only verifies that all radios are off.

I see the argument that there is a use case for the smartphone for taking pictures while operating without radios. But wouldn't a better solution then be a compact digital camera and a notebook? You can invent your own code for note taking that becomes arbitrarily hard to break. You can disguise a compact camera as a smartphone using just a case and a hot glue gun.

There is also the convenience factor. I do remove my battery frequently from my phone but it is too easy to just leave it on. People will generally not want to hassle with it if they don't have to.If security is easier and requires less effort then it lowers the cost and will be favored more often and it will protect more people.

There are also many times that people have been unhappy because I have my phone off and unable to reach me. There are also other times you want to be available.

Unfortunately, if your phone is owned then they can just exfiltrate the data when normal data transfer occurs. The data will still need to be stored for transmission later though.

With the iphone, you also need to monitor Bluetooth and WiFi in addition to cellular activity. Hopefully they will also monitor these.

Better yet, install a small custom switch that enables you to physically disconnect power from the battery without actually having to remove it from the phone.

Much less conspicuous if you're in public under physical surveillance, and provides options for phones with non-removable batteries assuming the right modifications are made.

Actually, regardless of whether or not smartphones have a removable battery, there's always a small second battery connected to the baseband for emergency purposes. I've confirmed this firsthand by taking apart several models, and you make out small coin cells on most online disassembly documentation as well.

The one in my old Atrix was a good 250mAh.

What would the baseband transmit in an emergency and how would it know that there was an emergency, if the phone itself had lost power?

When a phone is off or out of power, is the baseband periodically pinging cell towers?

I could see coordinates, e.g. of a lost party, or someone who called 911 but got disconnected by a low battery, that kind of thing. Cell phone pings can be extremely handy for SAR.

If it has a 250mAh battery then that is good for a continuous 1/4W transmission for 1 hour. But I imagine the batter is mainly there for the watchdog and RTC. Which is why you never have to set the clock every time you turn the phone on.

You don't need to set the clock when you turn on the phone because it gets the time from the network when it registers.

Pull your sim and battery. Reinsert the battery and turn the phone on. The time is still there, network or not.

Sure, I said as much in the comment above, and I also know and have tested that at least one common smartphone works just fine with this battery physically removed.

Always ? from the few (~10) cellphones I disassembled I remember nothing that looked like a cell.

Also how do you trigger an emergency call ? manufacturer embeds a special firmware so you don't have to boot the main OS and only use energy for the call ?

It could have been located away from view on the other side of the motherboard, as is sometimes the case.

As for what the full intended purpose and potential capabilities of these secondary batteries are, I have no idea since that's not documented. I do know that it's for a whole lot more than an RTC, however.

I stripped them completely. Unless it was a very slim cell that could be confused with an inductor, or hidden into some module (say camera block) ...

I'd love for it to be true though.

then store your phone in a Faraday cage like you have in your kitchen (probably)

Took me a second to get what you meant. But yes, I do in fact have one. The seals around the door are meant to be airtight rather than RF-tight, though, so it may or may not be good enough, depending on your purposes. If you want your phone to not transmit its position, it may not be good enough, but if you want it to not eavesdrop on you, it probably works.

> meant to be airtight rather than RF-tight

You are thinking about the wrong one.

They mean the microwave, not the fridge/freezer.

I thought he meant aluminum foil.

I've heard about this emergency capability for years, e.g earthquake, tsunami etc...But has anyone ever heard of it actually being activated for real?

Yes. Japan for earthquakes. But no evidence battery is not required.

citation please

(good luck, as this is false)

https://security.stackexchange.com/questions/65382/is-it-pos...

I'm not sure I like your attitude. This is readily available information

That's talking about a backup battery for the real-time clock on the phone. That type of battery is usually not rechargeable and doesn't support enough power to make any sort of call. I've never heard of an emergency backup battery for just the 'baseband' in any phone, but I am open to being proven wrong.

I don't mean to call you out, but I'm fairly positive this is wrong. I ran the baseband software team at Apple and worked on the first two generations of iPhones. I'm intimately familiar with that hardware having done reworks by hand myself on the first prototypes and being in all schematic reviews. They definitely didn't have secondary batteries connected to them. While this may exist on some new models of phone, I've never heard of it.

This doesn't even make much sense to me. Assuming you're talking about emergency calls, the application processor is necessary for dialing. You'd need to power the entire phone including the screen to make an emergency call.

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