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How do you know if the Signal client running on your phone right now doesn't include a backdoor? Sure it's open source. But how do you know how it was compile

How do you know if the Signal client running on your phone right now doesn't include a backdoor? Sure it's open source. But how do you know how it was compiled? What if someone changed the open source before shipping it to the app store?

i_am_proteus 4y ago
How do you know that the AES instruction set on your device's processor doesn't include a backdoor? Sure, the algorithm is public, but how do you know how it was implemented?
- upofadown 4y ago
  AES starts with 16 bytes and then encrypts it to 16 bytes. So there is no good place to hide extra data. Even a single bit that did not meet the AES spec for the key in use would produce complete garbage at decryption. So attempts to leak the key would at least leave a mark.
  - dividuum 4y ago
    Unless it’s a timing based leak..
bertman 4y ago
This is called "Reproducible Builds". https://signal.org/blog/reproducible-android/ https://signal.org/blog/reproducible-android/
- 100001_100011 4y ago
  Reproducible builds are for developers. As a user I didn't build the app on my phone. I have a phone with Signal on it. Tell me what I should do to verify it's running the open source Signal code.
  - bertman 4y ago
    If you, as a user, are concerned about reproducibility, you are no longer an average user. Thus, if you want this extra security, you can be expected to check the APK on your phone.
  - fgiox 4y ago
    Maybe you could figure this out yourself, and share your findings, rather than demanding answers from others?
  - 0xChain 4y ago
    You should check out Session. Their CTO apparently uses his PGP key to sign every release https://twitter.com/session_app/status/1514108746854985730 https://twitter.com/session_app/status/1514108746854985730
  - ghransa 4y ago
    Not perfect chain of custody but could report to virustotal (virustotal.com) and compare in a sandbox: https://play.google.com/store/apps/details?id=com.funnycat.virustotal https://play.google.com/store/apps/details?id=com.funnycat.v...
  - fsflover 4y ago
    Reproducible builds benefit the user by allowing independent checks of the software.
- RunSet 4y ago
  That page says: > the Signal Android codebase includes some native shared libraries that we employ for voice calls (WebRTC, etc). At the time this native code was added, there was no Gradle NDK support yet, so the shared libraries aren’t compiled with the project build. Also, assuming you trust the client, how to tell if the Signal server is running the published code, especially given Signal's track record of (not) publishing its source code? https://linuxreviews.org/Signal_Appears_To_Have_Abandoned_Their_AGPL-licensed_Server_Sourcecode https://linuxreviews.org/Signal_Appears_To_Have_Abandoned_Th...
  - kijiki 4y ago
    Signal server is explicitly untrusted in the Signal threat model, which is must be due to being based in a country (like any other country) with laws that can be used to compel actions on the server's owners. They publish legal orders they receive and their responses.
- pabs3 4y ago
  A related project that is also necessary for this, Bootstrappable Builds: https://bootstrappable.org/ https://bootstrappable.org/ Otherwise somewhere in the chain you are relying on binaries of unknown provenance.
bigDinosaur 4y ago
Have a classic: https://www.usenix.org/system/files/1401_08-12_mickens.pdf https://www.usenix.org/system/files/1401_08-12_mickens.pdf
Semaphor 4y ago
I would say it’s the usual. If someone with skills X (where depending on your knowledge and precautions, X can range from script kiddie to nation state) is after you specifically, you can only make their job harder, but unless you are very serious about security, you’ll probably get pwned. If you want general security, you can probably take it as given that someone checked the Signal build to be the one that the source is available for, and that no one intercepted just your download. But you still have to take some parts on faith, always, unless you build your own CPU and continue from there.
Genghis_9000 4y ago

i_am_proteus 4y ago

How do you know that the AES instruction set on your device's processor doesn't include a backdoor? Sure, the algorithm is public, but how do you know how it was implemented?

upofadown 4y ago
AES starts with 16 bytes and then encrypts it to 16 bytes. So there is no good place to hide extra data. Even a single bit that did not meet the AES spec for the key in use would produce complete garbage at decryption. So attempts to leak the key would at least leave a mark.
- dividuum 4y ago
  Unless it’s a timing based leak..

bertman 4y ago

This is called "Reproducible Builds". https://signal.org/blog/reproducible-android/ https://signal.org/blog/reproducible-android/

100001_100011 4y ago
Reproducible builds are for developers. As a user I didn't build the app on my phone. I have a phone with Signal on it. Tell me what I should do to verify it's running the open source Signal code.
- bertman 4y ago
  If you, as a user, are concerned about reproducibility, you are no longer an average user. Thus, if you want this extra security, you can be expected to check the APK on your phone.
- fgiox 4y ago
  Maybe you could figure this out yourself, and share your findings, rather than demanding answers from others?
- 0xChain 4y ago
  You should check out Session. Their CTO apparently uses his PGP key to sign every release https://twitter.com/session_app/status/1514108746854985730 https://twitter.com/session_app/status/1514108746854985730
- ghransa 4y ago
  Not perfect chain of custody but could report to virustotal (virustotal.com) and compare in a sandbox: https://play.google.com/store/apps/details?id=com.funnycat.virustotal https://play.google.com/store/apps/details?id=com.funnycat.v...
- fsflover 4y ago
  Reproducible builds benefit the user by allowing independent checks of the software.
RunSet 4y ago
That page says: > the Signal Android codebase includes some native shared libraries that we employ for voice calls (WebRTC, etc). At the time this native code was added, there was no Gradle NDK support yet, so the shared libraries aren’t compiled with the project build. Also, assuming you trust the client, how to tell if the Signal server is running the published code, especially given Signal's track record of (not) publishing its source code? https://linuxreviews.org/Signal_Appears_To_Have_Abandoned_Their_AGPL-licensed_Server_Sourcecode https://linuxreviews.org/Signal_Appears_To_Have_Abandoned_Th...
- kijiki 4y ago
  Signal server is explicitly untrusted in the Signal threat model, which is must be due to being based in a country (like any other country) with laws that can be used to compel actions on the server's owners. They publish legal orders they receive and their responses.
pabs3 4y ago
A related project that is also necessary for this, Bootstrappable Builds: https://bootstrappable.org/ https://bootstrappable.org/ Otherwise somewhere in the chain you are relying on binaries of unknown provenance.

bigDinosaur 4y ago

Have a classic: https://www.usenix.org/system/files/1401_08-12_mickens.pdf https://www.usenix.org/system/files/1401_08-12_mickens.pdf

Semaphor 4y ago

I would say it’s the usual. If someone with skills X (where depending on your knowledge and precautions, X can range from script kiddie to nation state) is after you specifically, you can only make their job harder, but unless you are very serious about security, you’ll probably get pwned. If you want general security, you can probably take it as given that someone checked the Signal build to be the one that the source is available for, and that no one intercepted just your download. But you still have to take some parts on faith, always, unless you build your own CPU and continue from there.

Genghis_9000 4y ago