391–400 of 474 posts
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The government is a plausible adversary for Signal
FWIW if it's the government, wouldn't they be able to just get direct access to Cloudflare logs - in real-time even - and thus observe and track the specific incoming connection to fetch the cached image?
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The person receiving it chooses to download images or whatever automatically though. I dunno, I'd still say the problem is at least 50% cloudflare. Why should they make which datacenters have a resource cached be obvious public knowledge? I do agree though, one could still end up inferring this information noisily by sending an attachment, waiting a while, and then somehow querying a lot of DCs and trying to infer ti…
Isn’t that because the URL parameters are so long that by design they effectively _are_ the password protection for the resource ? They shouldn’t be able to ‘leak’ to unintended recipients. Personally, like you I’m also not a huge fan of this, but URLs like that basically should be treated as the passwords. Don’t post them publicly / don’t give them out to people you don’t trust.
But agree with your statement here and others about the lifetime of the data - if something is sensitive or secret you want proper access controls applied, not just openssl rand -hex 8
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"Near a user" is also a big assumption. I'm ~200 miles to ORD and ~500 to IAD, but my ISP's peering & upstream arrangements mean Cloudflare serves my traffic 700 miles from DFW. But, at the same time: Cloudflare isn't going to serve me a cache from Seattle, Manchester, or Tokyo. Pinning down an unknown Signal user to even a rough geographic location is an important bit of metadata that could combine to unmask an indi…
Cloudflare does serve me from France. When I'm in Australia. (My ISP bought some IP addresses that were original regional France, back in the early 90s.) So though this does have implications, the assumptions they utilise, like always, are not universal.
CLoudflare uses anycast, and IP geo location is not how anycast works.
Unless I'm missing something, this seems like an incredibly long winded way to check the users IP location? For example, connecting to a VPN and checking https://cloudflare.com/cdn-cgi/trace gives me `colo:CPH` (Copenhagen) which is far from my nearest CF datacenter (geographically), closer to the IP location from my VPN provider (Oslo) but still not particularly close? If I don't use a VPN, I don't even get the capi…
So if you send a picture to a Signal user, it's retrieved via cloudflare, and cached in a data center near that user; now you can look up the cache status and find the data center used. I'd say "deanonymization" is stretching it, unless the user is in the middle of nowhere (no other users near the data center). But interesting writeup anyway.
Surprised signal doesn't have this option.
I only message people I know on Signal anyway.
Edit: it seems signal does have the option
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You can disable the auto-download. Settings > Data and storage > Media auto-download, you can choose what to auto download for mobile data/wifi/roaming.
Thank you! That's what I get for quick scrolling through the settings. I for sure thought it would have been under Privacy (for this concern), but that makes sense too.
Whatsapp has this option and I'm pretty sure it is in privacy settings.
It's "a very rough estimation of a user's location when they are not using a vpn".
Not sure why so many top comments dismiss the severity of this. This is just exactly the type of attack that give law enforcement or a malicious actor a way to establish proof of whereabouts.
For many commenters, it looks like deanonymization means unveiling highly sensitive info like name, address, email, etc.
For privacy-conscious individuals and hackers, it looks like it means 'revealing a data point that shouldn't be revealed'.
As a signal or Discord user, I would expect my country location not to be revealed to a person I don't know. So the latter definition makes sense to me.