Valid Signal privacy issues shrugged off while patches quietly rolled out
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Valid Signal privacy issues shrugged off while patches quietly rolled out
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Re: Valid Signal privacy issues shrugged off while patches quietly rolled out
#2Does the safety number count as a sort of hash in this case? Or is it absolutely nothing like an MD-5?
Re: Valid Signal privacy issues shrugged off while patches quietly rolled out
#3Does the safety number count as a sort of hash in this case? Or is it absolutely nothing like an MD-5?
I don’t know if it’s actually a hash, but it’s probably some kind of diffuse one-way function: it would need to be impossible to pre-image or reproduce from a different input in order to serve its purpose.
Edit: Signal’s blog refers to it as a hash[1]. It’s apparently essentially just a hash of the contact’s public key, so rotating that causes the hash change.
Re: Valid Signal privacy issues shrugged off while patches quietly rolled out
#4Does the safety number count as a sort of hash in this case? Or is it absolutely nothing like an MD-5?
My understanding was that it was a fingerprint of the public key, much like an SSH fingerprint.
Re: Valid Signal privacy issues shrugged off while patches quietly rolled out
#5I was expecting to hear about someone who got a new phone, set up Signal using the phone number, and then communicated with contacts without any more authentication.
This doesn't appear to be anything of the kind. Signal has implemented a migration system so that people can move to a new phone without changing the safety number.
Then a bunch of references to the promises Signal makes about re-verifying if the safety number changes. Since the safety number doesn't change, none of those actually apply.
Re: Valid Signal privacy issues shrugged off while patches quietly rolled out
#6All that text for a feature that no one, including the author uses correctly. Messaging your mates to reassure them everything is correct via Signal after you update your device and your safety number changes is pointless.
The main function of safety numbers is to theoretically prevent mass mitm of Signal.
Re: Valid Signal privacy issues shrugged off while patches quietly rolled out
#7Does the safety number count as a sort of hash in this case? Or is it absolutely nothing like an MD-5?
The "safety number" also encodes both participants phone numbers (the verifier and the person to be verified). So you would be a little foolish to publish it in say, a blog post if you weren't intending those phone numbers to be public information. I'm also very amused that the author censored part of the QR code, but not the human readable text below it containing the exact same data.
Re: Valid Signal privacy issues shrugged off while patches quietly rolled out
#8TL;DR of article: Signal transfers key material upon migrating to a new device if you use the "transfer messages" workflow. As a result, safety numbers do not change.
I don't see how this is a problem at all. This was actually a feature that many Signal users wanted to use - they didn't want to re-verify safety numbers every time that they had to reinstall Signal or switch to a new phone.
> We don't want anyone to get hurt by way of trusting privacy guarantees which may be more conditional than they appear from the docs!
> If Bob notices the chat safety number with Alice has changed and then Alice sends a bunch of suspect-sounding messages or asks to meet in person and Bob has never met Alice in person before, for example, Bob should be wary. After Alice for example is forced to provide device passcode or unlock their device with their fingerprint or face, Alice's device could be cloned over to a new device by way of quick transfer functionality without Alice's consent, and the messages could be coming from the cloned device rather than Alice's actual device.
Respectfully, this doesn't make any sense. Signal provides security from device to device, it doesn't stop someone from pointing a gun to your head and looking at your messages or pretending to be you after stealing your phone. If someone has the physical possession of your phone necessary to perform a device transfer, then you're already screwed. The idea that a safety number change would alert the person on the other end that you're being held hostage is outlandish and is completely divorced from any normal use of Signal.
Re: Valid Signal privacy issues shrugged off while patches quietly rolled out
#9I was expecting to hear about someone who got a new phone, set up Signal using the phone number, and then communicated with contacts without any more authentication. This doesn't appear to be anything of the kind. Signal has implemented a migration system so that people can move to a new phone without changing the safety number. Then a bunch of references to the promises Signal makes about re-verifying if the safety…
I imagine there is a human factors tradeoff here. If signal notified on each migration, users with even medium sized contact lists would likely be getting constant notifications - making the alert useless. See medical device or aviaton alerts experiences.
Re: Valid Signal privacy issues shrugged off while patches quietly rolled out
#10I raised a similar issue 4 years ago - https://github.com/signalapp/Signal-Android/issues/6703
Signal used to silently fail if you changed device. I guess not much has changed.