5 ms·

That would be the way to do it.

by Canada 7y ago

sneak 7y ago
All of my signal desktop clients seem to update automatically, downloading new code and prompting me to restart the app to run it. With such opaque, basically-RCE privileges assumed by the app, I am not sure what would stop a malicious insider from sending an update to silently replace the sgx keys or certs (or shipping any other targeted secret exfiltration code). Seems to me that with the client autoupdate, this would be a much easier nut to crack than the secure enclave (not to disparage the work on the defense-in-depth). It just seems like a ton of work and complexity to me for not a ton of benefit considering the existing threat models. Good on them for making the attempt, though.
- cjbprime 7y ago
  This is a super interesting problem! It applies to basically all desktop autoupdaters. Note that App Stores are in a better place -- as far as I know they don't make it possible to target users with malicious updates, you'd have to push the malicious update to everyone at once. Some anonymity wins for desktop apps are downloading updates over Tor (to prevent the update server knowing who you are by your IP) or Bittorrent (to prevent the ability to offer an update to someone without offering it to everyone), and checking that you're being offered a binary whose hash is published publicly (e.g. to a blockchain). But then you start hitting increased code surface problems and those systems not working on some networks. I think Tor's Firefox browser does the anonymous Tor update thing; that's probably the best in class here.
  - novok 7y ago
    Well the app store can be compelled to push unique updates. It's more work, but it isn't an impossibility.
    - cjbprime 7y ago
      Do you have an example of how?
      - saagarjha 7y ago
        Presumably you'd be able to if you put a selection of engineers at gunpoint.
        cjbprime 7y ago
        I mean, we're talking about engineers from two different companies at this point, right? Presumably the Foo App engineers have to prepare and sign a malware version of Foo and then you have to go coerce a bunch of Apple engineers to send the iOS update to specific phones. Once your conspiracy theory involves multiple uncoordinated groups, the chance of it remaining secret basically goes to zero. Once you stop holding people at gunpoint they're going to tell someone what you did. Once it's known that Apple targeted malware at some of its users, its reputation will crash. So Apple would probably resist this as strongly as it can, which is probably pretty strongly given that it's the most valuable public company in the entire world. Am I missing something? This is not sounding like a plausible conspiracy theory so far.
        saagarjha 7y ago
        Why to talk to the Foo App people when you can make your own malware version of Foo App?
        sneak 7y ago
        It's not a conspiracy theory if the proposed scenario is the DOJ says to Apple in a lawful wiretap order "you must push this wiretapped messaging app update to phone identified by IMEI 12345". Wiretaps and stored comms records subpoenas are commonplace things, and the DOJ is entirely capable of contracting someone to quickly produce a specially-modified wiretap version of any app available on the app store (it's not a terribly difficult technical hurdle), even the ones that aren't open source. Whether or not Apple would cooperate by providing the appropriate app signature and shipping it to the phone or not is another question. There is of course the legal argument that creating a cryptographic signature against their will is compelled speech and thus they have the right to fight or refuse. Personally, I doubt they'd fight very hard, provided the whole thing were kept secret (which would be in the interest of both Apple and the DOJ). Apple knows quite well that you can't fight city hall (or the CCP). The wiretapped iCloud servers in China are a perfect example of Apple's reputation remaining intact despite shipping a nationwide backdoor for a government to millions of their iPhone and iPad customers. After all, they'd always have the standard "we received a lawful wiretap order, signed by a federal judge, appropriately limited in scope to a single suspect, with which we were legally required to comply" fallback.
- tptacek 7y ago
  Especially since virtually every other secure messaging system simply stores the information Signal is discussing here in plaintext, indexed in SQL databases running in their cloud environments.

That would be the way to do it.

by Canada 7y ago

That would be the way to do it.

All of my signal desktop clients seem to update automatically, downloading new code and prompting me to restart the app to run it. With such opaque, basically-RCE privileges assumed by the app, I am not sure what would stop a malicious insider from sending an update to silently replace the sgx keys or certs (or shipping any other targeted secret exfiltration code). Seems to me that with the client autoupdate, this would be a much easier nut to crack than the secure enclave (not to disparage the work on the defense-in-depth). It just seems like a ton of work and complexity to me for not a ton of benefit considering the existing threat models. Good on them for making the attempt, though.

cjbprime 7y ago
This is a super interesting problem! It applies to basically all desktop autoupdaters. Note that App Stores are in a better place -- as far as I know they don't make it possible to target users with malicious updates, you'd have to push the malicious update to everyone at once. Some anonymity wins for desktop apps are downloading updates over Tor (to prevent the update server knowing who you are by your IP) or Bittorrent (to prevent the ability to offer an update to someone without offering it to everyone), and checking that you're being offered a binary whose hash is published publicly (e.g. to a blockchain). But then you start hitting increased code surface problems and those systems not working on some networks. I think Tor's Firefox browser does the anonymous Tor update thing; that's probably the best in class here.
- novok 7y ago
  Well the app store can be compelled to push unique updates. It's more work, but it isn't an impossibility.
  - cjbprime 7y ago
    Do you have an example of how?
    - saagarjha 7y ago
      Presumably you'd be able to if you put a selection of engineers at gunpoint.
      - cjbprime 7y ago
        I mean, we're talking about engineers from two different companies at this point, right? Presumably the Foo App engineers have to prepare and sign a malware version of Foo and then you have to go coerce a bunch of Apple engineers to send the iOS update to specific phones. Once your conspiracy theory involves multiple uncoordinated groups, the chance of it remaining secret basically goes to zero. Once you stop holding people at gunpoint they're going to tell someone what you did. Once it's known that Apple targeted malware at some of its users, its reputation will crash. So Apple would probably resist this as strongly as it can, which is probably pretty strongly given that it's the most valuable public company in the entire world. Am I missing something? This is not sounding like a plausible conspiracy theory so far.
        saagarjha 7y ago
        Why to talk to the Foo App people when you can make your own malware version of Foo App?
        sneak 7y ago
        It's not a conspiracy theory if the proposed scenario is the DOJ says to Apple in a lawful wiretap order "you must push this wiretapped messaging app update to phone identified by IMEI 12345". Wiretaps and stored comms records subpoenas are commonplace things, and the DOJ is entirely capable of contracting someone to quickly produce a specially-modified wiretap version of any app available on the app store (it's not a terribly difficult technical hurdle), even the ones that aren't open source. Whether or not Apple would cooperate by providing the appropriate app signature and shipping it to the phone or not is another question. There is of course the legal argument that creating a cryptographic signature against their will is compelled speech and thus they have the right to fight or refuse. Personally, I doubt they'd fight very hard, provided the whole thing were kept secret (which would be in the interest of both Apple and the DOJ). Apple knows quite well that you can't fight city hall (or the CCP). The wiretapped iCloud servers in China are a perfect example of Apple's reputation remaining intact despite shipping a nationwide backdoor for a government to millions of their iPhone and iPad customers. After all, they'd always have the standard "we received a lawful wiretap order, signed by a federal judge, appropriately limited in scope to a single suspect, with which we were legally required to comply" fallback.
tptacek 7y ago
Especially since virtually every other secure messaging system simply stores the information Signal is discussing here in plaintext, indexed in SQL databases running in their cloud environments.