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"The APK direct download doesn’t even accomplish the stated goal of “harm reduction”. The user has to manually verify the checksum, and figure out how to do it

"The APK direct download doesn’t even accomplish the stated goal of “harm reduction”. The user has to manually verify the checksum, and figure out how to do it on a phone, no less. A checksum isn’t a signature, by the way - if your government- or workplace- or abusive-spouse-installed certificate authority gets in the way they can replace the APK and its checksum with whatever they want." This is true for just about every single piece of software that one downloads. But nice job deflecting it onto Signal to solve for you. Installing an APK by hand is not difficult either, you transfer it to your phone and open it. I don't see how Signal is doing any better or worse of a job from similar apps. Also, Signal's checksum verification is SHA-256 which I'd say is "good enough." It's also being served from an HTTPS webpage. Is there something missing here?

jhasse 8y ago
Signal doesn't need to solve it, because F-Droid would.
shittyadmin 8y ago
Additionally with Android APKs, the APK has to be signed and additional updates will be verified to match the same vendor.
- Bartweiss 8y ago
  Which as far as I can tell is what Marlinspike meant by harm reduction. It's not preventing anyone from hijacking your encrypted session and serving you a bad app, I'm not sure how it could. ("How do you secure your connection given that your security has already been silently compromised?" isn't a question I really understand.) But it helps ensure that people are at least requesting the genuine app, and if they get it then they'll get signature verification for future versions.
Vinnl 8y ago
And that's not even what Moxie meant by "harm reduction" - he meant that he wanted to stop people downloading APKs from random third parties, which has surely been pretty much accomplished.
Bartweiss 8y ago
A lot of the complaints here appear to actually be "if you download software, or run that software on Android, or on any third party hardware at all, it could be compromised", but with Signal singled out. For a given user, I don't understand how signing is better than a checksum under this threat model. Going online to download an app is not part of an established connection with that app, so an attacker could simply serve you a page of their choosing with a signature they issued. Verifying identity for an initial connection is definitionally what signatures can't solve. I think, maybe, the idea is that a signed app could reject communications from unsigned/mis-signed installations? So if someone has entirely hijacked your session and served you a fake app, you won't be able to communicate with the rest of the network. It sounds like a coherent model at least: you can protect single targets by verifying their software when they try to communicate. (If so, I don't understand how that meshes with the call to federate Signal, which would require it to accept signatures from outside parties. Is the idea something like a CA web-of-trust where only people approved by accepted signers can federate their apps?)

jhasse 8y ago

Signal doesn't need to solve it, because F-Droid would.

shittyadmin 8y ago

Additionally with Android APKs, the APK has to be signed and additional updates will be verified to match the same vendor.

Bartweiss 8y ago
Which as far as I can tell is what Marlinspike meant by harm reduction. It's not preventing anyone from hijacking your encrypted session and serving you a bad app, I'm not sure how it could. ("How do you secure your connection given that your security has already been silently compromised?" isn't a question I really understand.) But it helps ensure that people are at least requesting the genuine app, and if they get it then they'll get signature verification for future versions.

Vinnl 8y ago

And that's not even what Moxie meant by "harm reduction" - he meant that he wanted to stop people downloading APKs from random third parties, which has surely been pretty much accomplished.

Bartweiss 8y ago

A lot of the complaints here appear to actually be "if you download software, or run that software on Android, or on any third party hardware at all, it could be compromised", but with Signal singled out. For a given user, I don't understand how signing is better than a checksum under this threat model. Going online to download an app is not part of an established connection with that app, so an attacker could simply serve you a page of their choosing with a signature they issued. Verifying identity for an initial connection is definitionally what signatures can't solve. I think, maybe, the idea is that a signed app could reject communications from unsigned/mis-signed installations? So if someone has entirely hijacked your session and served you a fake app, you won't be able to communicate with the rest of the network. It sounds like a coherent model at least: you can protect single targets by verifying their software when they try to communicate. (If so, I don't understand how that meshes with the call to federate Signal, which would require it to accept signatures from outside parties. Is the idea something like a CA web-of-trust where only people approved by accepted signers can federate their apps?)