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> Signal has open clients with reproducible builds. Not really. First of all, there is only one Signal client allowed to connect to Signal’s servers. And in th

> Signal has open clients with reproducible builds. Not really. First of all, there is only one Signal client allowed to connect to Signal’s servers. And in the real world, the vast majority of Signal uses are getting their APK for that app from the Google Play store (the Signal team has said that they prefer you to use the Play store as well, instead of direct-downloading an APK from their website which they offer only grudgingly). That means that a state-level actor could possibly carry out a targeted attack to replace the Signal app on a given person's phone with a malicious build. Also, Signal’s reproducible build system requires a specific version of the Android development kit. It has been pointed out that a state-level actor could be sitting on vulnerabilities in that, and not in the Signal source code itself.

codethief 6y ago
> That means that a state-level actor could possibly carry out a targeted attack to replace the Signal app on a given person's phone with a malicious build. No, they couldn't. They would need the Signal developers' key. Android requires app updates to be signed with the same key as the original app.
- cyphar 6y ago
  A state-level actor can get the Signal key either covertly or by simply marching into the Signal offices with either a warrant or (if that fails) guns. Now, whether that will actually happen is a secondary issue -- but I submit that you have a mistaken conception of what a "state-level actor" means in a threat model. The fact that Google Inc doesn't hold the necessary keys but Signal LLC does is not a meaningful distinction to a state-level actor. That isn't to say "all crypto is hopeless", simply that you shouldn't consider Signal to be state-level actor proof.
monocasa 6y ago
The point isn't to build your own and use it; it's to verify that the binary in the app store matches the source they published.
- cyphar 6y ago
  Do you personally do that with every release (which happens every few weeks or so)? Do you know anyone who does that who is trustworthy? If not, it's a fairly useless form of protection.
lallysingh 6y ago
Both these attacks indicate a problem that doesn't have anything to do with using Signal. If the actor can replace apps on your specific phone, then you're pretty fucked no matter what app you use. If the attack is on the android dev kit, but not on signal, then.. the attack isn't on Signal, it's on the dev kit. Unless Signal's using an unusual version of the dev kit, your risk exposure to this attack is equal to any other app that you would use instead of Signal.

codethief 6y ago

> That means that a state-level actor could possibly carry out a targeted attack to replace the Signal app on a given person's phone with a malicious build. No, they couldn't. They would need the Signal developers' key. Android requires app updates to be signed with the same key as the original app.

cyphar 6y ago
A state-level actor can get the Signal key either covertly or by simply marching into the Signal offices with either a warrant or (if that fails) guns. Now, whether that will actually happen is a secondary issue -- but I submit that you have a mistaken conception of what a "state-level actor" means in a threat model. The fact that Google Inc doesn't hold the necessary keys but Signal LLC does is not a meaningful distinction to a state-level actor. That isn't to say "all crypto is hopeless", simply that you shouldn't consider Signal to be state-level actor proof.

monocasa 6y ago

The point isn't to build your own and use it; it's to verify that the binary in the app store matches the source they published.

cyphar 6y ago
Do you personally do that with every release (which happens every few weeks or so)? Do you know anyone who does that who is trustworthy? If not, it's a fairly useless form of protection.

lallysingh 6y ago

Both these attacks indicate a problem that doesn't have anything to do with using Signal. If the actor can replace apps on your specific phone, then you're pretty fucked no matter what app you use. If the attack is on the android dev kit, but not on signal, then.. the attack isn't on Signal, it's on the dev kit. Unless Signal's using an unusual version of the dev kit, your risk exposure to this attack is equal to any other app that you would use instead of Signal.