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The clever cryptography behind Apple’s “Find My” feature
- OJFord 7y agoI keep reading that Apple already randomises MAC addresses for privacy purposes, but then how do its devices stay logged in to 'captive' WiFi, or more problematically, paired with Bluetooth devices? Are the addesses only randomised for broadcast / new pairs?
- nerdbaggy 7y agoI only know about the WiFi, once you start the attempt to connect to the SSID it uses your real mac. So the probing uses random MAC address
- convivialdingo 7y agoThe hard part is going to be the key rotation. I’d suspect they’re using something similar to Moxie’s Double Ratchet algorithm since it’s got some years of real world usage. https://en.m.wikipedia.org/wiki/Double_Ratchet_Algorithm https://en.m.wikipedia.org/wiki/Double_Ratchet_Algorithm
- StavrosK 7y agoOr maybe they just hash the time and a pre-shared key to generate ECC keypairs, since communication is one-way.
- convivialdingo 7y agoCould be - but time would be something easily guessable if you knew the public key. Still not bad though since the public keys are being stored on the devices.
- StavrosK 7y agoHow would it be guessable if you're hashing it with a random string?
- convivialdingo 7y agoPublic keys are essentially trackable metadata if they're shared. The proposed hash of time + public key would be guessable if you had access to a particular public key. Apple certainly could get the public key. They wouldn't know specifically what data was in the encrypted message, but with enough attributes (IP, time, Apple ID, etc) they could obviously gather a high-confidence amount of tracking data still.
- StavrosK 7y agoI said "time and pre-shared key". The public key doesn't enter into it.
- convivialdingo 7y agoSure - that's a solution - Apple's iCloud Keychain might work there also. I don't use it and have some reservations as Apple’s iCloud services still do not provide end-to-end encryption. I'd be interested to see what Matt Green has seen.
- callmeal 7y agoThis was to be expected, given that apple has been slowly taking away the ability to physically turn off your device. Isn't anyone else concerned about the fact that a shutdown laptop will continue to broadcast defying convention and expectations?
- jhabdas 7y agoApple's Find My features are what turn iPhone theft into complete iCloud vulnerabilities. This was first seen with the social engineering attacks made possible in Find My iPhone. All an attacker needs to do is spoof an SMS and phish your account credentials. It's likely this feature too will lead to clever hacks used to further damage users.
- snorrah 7y agoHow, exactly ?
- jhabdas 7y agoFirst forensics to try and crack the pass code (takes about 2 days). Next turn on the phone just long enough to take down the phone number provided. Then wait another day or so and turn on the phone again. At the same time send the recovery number an SMS linked to a fake iCloud website and grab the credentials when they log-in. I have concrete examples of the processes, tools and servers used to pull this off. Apple Support is aware this is a common occurrence - they told me so over the phone. If you'd like to know more specifics, please feel free to contact me.
- rphlx 7y agoThe Wired article is not detailed enough to definitively poo-poo this scheme, but I am pretty skeptical about some of the claims, given a) how easy it is to map an IP to a coarse location, b) how easy it is to map many IPs to a small number of already-known humans/users. That is to say: the asym crypto may strongly protect the precise (GPS or LTE triangulation) location from Apple and from others, but I do not see how a cloud-based system can ever hide coarse location from Apple and/or from governments as, given the short range of BT, they can reliably infer that a device (and hence its owner) is/was near whatever IP sends the encrypted precise location to their cloud. Then it's just a matter of mapping the device's "randomized" ID back to an actual user/phone. That seems easy enough as soon as a second device accesses it from an IP that's mappable to a specific residential address, Apple account, etc. e.g. A and B both log into iTunes or some other Apple service using a@apple.com and b@apple.com from HOMEIP at some point in the past. HOMEIP is never used by any other Apple accounts. A(lice) and B(ob) exchange a secret and otherwise begin participating in this "private" tracking scheme. A goes out shopping and while there it pushes its encrypted precise location to the Apple cloud, using random ID 424242, from MALLIP. Perhaps A's device sends it directly, or perhaps it's relayed from BT to Mall wifi to Cloud by C's device if A has both LTE and wifi disabled. A few minutes later S(omeone) requests encrypted location for random ID 424242, from HOMEIP. Apple (and any government compelling it to share information) can reliably infer that "Someone" was A or B attempting to track either B or A, and that the tracked phone was at/near the business address of MALLIP - their coarse location - even if they can't decrypt the precise location without the secret key. If you know from public records that A and B are married, and assume that women are more likely to be at a mall on their own than men, you may further assume that A is at the Mall while B is at home. Result: the "private"/"encrypted" precise location beaconing has an unfixable metadata side channel that will leak coarse location data to Apple and to any governments that compell it.
- moreira 7y agoWhat you're saying is basically that this scheme will leak the IP address you're on, because that's just how the internet works. There's... not much that can be done about that, and there's no need for the scare quotes on the words private or encrypted. Any encrypted communication still uses an IP address that can be mapped to a coarse location; this isn't an Apple related thing. If you want to be able to find your device (it's opt-in), it needs to relay its location via the Internet. Doing so requires an IP address, which can indeed be mapped to a coarse location in some cases (my own home IP address is totally useless, it says I'm in London when I'm on the other side of the country). I'm not sure what the big deal is.
- sansnomme 7y agoIt's simply amazing how Apple could make P2P mesh networking viable for production use. This is highly inspiring!
- nonamechicken 7y agoI am not sure if it's the same technology, The Weather Channel App (Android) has an option for mesh network based alerts. https://weather.com/apps/ibm/meshnetworkalerts https://weather.com/apps/ibm/meshnetworkalerts
- tomputer 7y agoInstead of only finding the location of my stolen device, what I really would like is using this to remote wipe my device, before someone else can or will turn it on (if it has been turned off). Because it is not like I will fly to some other country to catch the thief or new owner of my stolen device.
- zapzupnz 7y agoThat's a feature of Find My, and has been for years on iOS. They're bringing it to macOS this year for devices with a T2 chip (the newer MacBooks, basically).
- mikorym 7y agoAre you sure about that? The impression I got from their summary is that the bluetooth locations are passive. An aside: what would happen if you wipe macOS and install another base operating system.
- celeritascelery 7y agoYou can’t. With Catalina the device is activation locked, meaning you need the original iCloud credentials to install a new OS.
- zapzupnz 7y agoTo clarify: this applies to a Mac that has been locked. That is, if the Mac is locked with Activation Lock, it wouldn't be possible to install another OS; the firmware itself will lock the user out of the computer entirely until the machine is unlocked. This dissuades thieves from stealing your MacBook as it will effectively be useless for anything other than parts, and most thieves aren't in the tiny-amounts-of-aluminium-relative-to-if-they-just-stole-cars recycling business. I clarify because I don't want anybody thinking one is entirely unable to install another OS at all. That is possible, but of course you lose out on macOS features like Activation Lock.
- mikorym 7y agoShort summary: 1. At setup, Find My generates private key shared to all your Apple devices. 2. The private key generates a perpetual sequence of public keys. These change (iterates to the next) "frequently". 3. The rotating public key is shared accross all (including other people's) Apple devices via Bluetooth and can even do this when it's off. 4. The shared scheme pings to Apple's central system and uploads A. hashes of the public keys in the area and B. the location. 5. When you try to find a device you send your hashed public key to Apples server and they return the last picked up location (encrypted). (You thus need at least 2 Apple devices, one to find the other. Also, they don't say how the previously iterated public keys are remembered.)
- omk 7y agoThis seems very very impressive. But I have so many questions still. The most important one being, there has to be a way to reset these tracking keys for cases like - Resell - Loss of a companion device that was never found and it took the private keys with it - Got a new companion device How do I reset the keys and how do I make sure a theif can't reset these?
- Angostura 7y agoIf it is the same as with the Existing Find My Phone 1. Resell - you turn off 'Find My' on your phone and sign out of iCloud then wipe the device 2. Loss - Go into iCloud and mark the device as lost. Not sure what this means for finding other devices 3. New companion device - sign it into iCloud.
- tim333 7y agoI'm guessing that if you log into the device with your apple id you can reset the private keys, otherwise not?
- slim 7y agodoes this mean my device will be relaying datagrams even if I did not enable "Find My" feature? Supposing apple can't infer the precise location, of every user, they still can infer the social graph
- dkoston 7y agoThey aren’t using your social graph, they are using location proximity and transmitting the data inside existing packets sent to cell towers for connectivity purposes. There’s already a ton of information passing to cell towers to identify and negotiate connections with phones that could be used to infer your social graph. You’d have to correlate that with a geo location database that knows about what type of locations you visit as there would be tremendous amounts of false signals at public places like restaurants and malls. Long story short, Apple, cell tower operators, and mobile providers already have all the data they’d need to make these graphs. If this functions as designed, it will contain much less information and wouldn’t be useful for this purpose (I.e. encrypt requests and don’t pass IP info with them to any systems that have the ability to decrypt them. If you make a few hops to the systems which have the ability to decrypt them and don’t share correlation IDs or the origin IP, there’s no way to correlate these requests back to which device sent them or what IP or cell tower it had).
- nayuki 7y agoThe feature of rotating public keys to enhance privacy is already used in cryptocurrencies, especially in the underpinnings of Monero. Here's one thread discussing how to make a mechanism to generate new public keys on demand: https://crypto.stackexchange.com/questions/58022/a-method-to-receive-payments-at-obscured-addresses https://crypto.stackexchange.com/questions/58022/a-method-to...
- cyphunk 7y agoIs the connectivity layer considered: Is the 3rd party "proxy" handler uploading the information using an Apple ID? Does Apple record, store IP information? It seems to me that by using this system you volunteer to send data to Apple constantly which may not reveal your GPS location but will reveal your network location. I'm happy to see someone trying to innovate in this space. I still wonder if it is okay for journalists and risk affected users to use this or if they should be advised to avoid it.
- ape4 7y ago"also to keep Apple itself from learning device locations, even as it allows you to pinpoint yours."
- bonestamp2 7y agoThere is always the risk of rogue employees, but what they're probably talking about here is that they also can't be compelled to reveal the location by someone else. They probably don't want to actually say that since it might be misconstrued as trying to skirt the law or being uncooperative with law enforcement.
- tinus_hn 7y agoThey have already been halfway in a lawsuit about that, it’s great marketing.
- 0xffff2 7y agoIsn't the explicit goal of a feature like that to be uncooperative with law enforcement? Who else is going to (attempt to) compel them to reveal user location data?
- angott 7y agoNot just that. Say they have a security breach... if there is no data, no data gets leaked.
- bonestamp2 7y agoIt's not that they're trying to be uncooperative with law enforcement though -- the fact that it prevents law enforcement from getting location data is a side effect of protecting privacy from everyone (marketers, hackers, etc) rather than it being the explicit purpose of keeping it from law enforcement. Which is why they probably want to be very careful about how they word it -- because some people might see it as the purpose rather than the side effect.
- RcouF1uZ4gsC 7y agoWhile quoted in the article, Matthew Green’s writeup provides a lot of neat ideas on how it may actually work https://blog.cryptographyengineering.com/2019/06/05/how-does-apple-privately-find-your-offline-devices/ https://blog.cryptographyengineering.com/2019/06/05/how-does...
- lixtra 7y agoIt feels like that can be exploited in some ways. As a first thought it reduces the privacy of the reporting 3rd party phone. I.e. I can leave a fully charged phone in my wife’s car and track her for weeks while she will have the burden to recharge her phone for network/gps power. A regular gps tracker would need much more energy. Edit: another scenario, leave it in an isolated hut. If I get a signal, someone is close to the hut. Edit 2: if I piggy back the protocol and can manipulate the key schedule (chose key A or B) then I can leak one bit of information through the third party phone. The third party phone may be allowed to communicate while my sender isn’t.
- rando444 7y agoPlaces like shopping malls use just your devices hardware ids to track your movements. To me just the fact that these things are on when you ask for them to be off is problematic.
- slig 7y agoiOS does shuffle the MAC address in order to prevent this, doesn't it?
- djchen 7y agoYes, except if you connect to their WiFi.
- oflannabhra 7y agoYes, on top of this, applications don’t have access to a devices MAC address through CoreBluetooth, so they can’t fingerprint a device.
- baybal2 7y agoYou can shuffle your mac but not your gsm/3g ids broadcasted in the open as per spec. I first saw this tech, I think, 9 years ago when I first encountered a "bluetooth spam" device
- lixtra 7y ago
- xattt 7y agoThis seems to be leading to the stealth reveal in the fall for a positioning system augmented by device-to-device positioning.
- contravariant 7y agoSo you can only find your phone if it's close to another (compatible) apple appliance?
- knolax 7y agoIf the phone is broadcasting the public key couldn't some malicious actor simply send the wrong location? Also couldn't they simply put it in a faraday bag or wrap in some tin foil?
- mr_toad 7y agoI doubt they’d have to bother - I doubt that the police will do anything even if you provided them a location. I’ve never known the police to do anything about stolen property. Even stolen cars don’t seem to be investigated.
- JumpCrisscross 7y ago> couldn't they simply put it in a faraday bag or wrap in some tin foil? Yes, but (1) that increases the difficulty of stealing such devices and (2) doesn’t help opportunistic or stupid thieves. Nobody is claiming that Find My makes Apple products unstealable.
- vbezhenar 7y agoLocation is encrypted with key, so just faking particular location is impossible. And I guess, they'll transmit some incrementing number or timestamp to fight re-transmission attacks.
- tucif 7y agoThe nearby phone is the one encrypting its own location with the public key broadcasted, so in theory fake location is possible if you had control over the protocol in all nearby devices.
- comex 7y ago> Also couldn't they simply put it in a faraday bag or wrap in some tin foil? If you're a thief and you want the phone to stop broadcasting, AFAIK you can just turn it off (as opposed to leaving it in sleep mode). But you'll have to deal with Activation Lock, which has been around for years and makes the phone a brick without the original owner's Apple ID. The new feature, on the other hand, is more applicable to devices that are just lost, not stolen.
- mekazu 7y agoSounds similar to P2PE.
- lifeisstillgood 7y agoI am reminded of a section in Neal Stephenson's The Diamond Age where (some guy) takes a whole day to track the history of the young protagonist in an internet cafe - and an explanation of passing packets between passing devices as if handing parcels to random strangers as they walk down the street always stuck in my mind This seems to be saying that Apple has a big mesh network play ready sometime soon. Want to bet they have a good idea of coverage already and need some testing - they might not be able to see your location but they will see the location of every phone passing your public key encrypted bits back - they get to test their mesh network ? Or am I missing something?
- lixtra 7y ago> see the location of every phone passing your public key encrypted bits back My understanding is that (in this scheme) all location data is encrypted by keys unknown to apple, i.e. the reporter uses the lost device’s public key to encrypt its location and transmits it together with the hash of the key. However, apple seems to be able to infer proximity of two reporters, as described here https://news.ycombinator.com/item?id=20135995 https://news.ycombinator.com/item?id=20135995 Edit: except if the Lost device is controlled by Apple, then they can decrypt the location of the reporting device.
- parrellel 7y agoThat was my thought too, and God I hope so. Someone needs to push mesh networking on a more consumer level, if it has to be Apple, so be it.
- edgineer 7y agoThere is one consumer push for a mesh-networking phone that was in the news recently, Volk Fi. Their idea is to use 900MHz radios in smartphones to hop several miles to the nearest wired hub, alongside a cellular SIM, where a hub owner earns credit for data relayed through it. Some pessimism surrounds them though.
- tyingq 7y agoIs this scheme where the public key can somehow rotate on it's own, while still being decryptable by the unrotated private key a new thing? I had not heard of it before. Edit: This other comment in the thread points at an article with some guesses as to how it might work. It mentions a system called Elgamal that has a scheme somewhat like my description above: https://news.ycombinator.com/item?id=20134956 https://news.ycombinator.com/item?id=20134956
- mrb 7y agoI'm sure it's an oversimplification of the description of the protocol. For example Apple could use a "base private key" that's just a seed fed to a CSPRNG to generate a series of EC private keys. The client can then rotate through this series of keys, while the "base private key" never changes.
- chronogram 7y agoPlease! http://its-not-its.info/ http://its-not-its.info/ Why is it so easy for nth language learners and so annoying to read. Edit: guessing by the downvotes it's just me being annoyed by it. Well, sorry HN. Seeing as it's so hated to be annoyed by it's and its, should I make some public apology or something?
- tyingq 7y agoI dunno, but you missed a question mark at the end there.
- chronogram 7y agoYes? Maybe you're right. It was intended to be a desperate plea at wanting readable English from generic English comments, therefore I did not include a question mark, as it was a plea. You might be right though!
- tyingq 7y agoYou know why the "it's" mistake is common. Edit: Because people get used to adding 's to indicate possession. I don't always do it, but it happens.
- taxidump 7y ago>Matthew Green, a cryptographer at Johns Hopkins University. "Even if I tracked you walking around, I wouldn’t be able to recognize you were the same person from one hour to the next." Thos sounds like a great way to track shoppers in, for example, a shopping mall. If the BLE beacon is broadcasting at a predetermined rate this may also extend tracking past the rotation of keys right?
- ngcc_hk 7y agoClever ... ??!!! Still miss the larger picture. Now the genie is out, a country will have technology to monitor all things and people all the time. The world is not just Apple. Someone will use the sane idea to do evil behind this. And even Apple has to work inside say china and follow their law. What if they ask ... We have been here before. Internet ! The links to us all. The freedom to publish and share. Then someone turn it into a way to record and monitor everything you said. And e-wall the whole country and round up any people they do not like. Good luck. Guess technology is neutral. It is not it’s fault. But beware of the gift from clever Greek. Or in that story the golden Apple.
- dmitriid 7y ago> Now the genie is out, a country will have technology to monitor The genie has been out for a long time. Apple is using existing technologies to achieve this > Someone will use the sane idea to do evil behind this. Where have you been the past few years? You are already being tracked everywhere.