[bigbones]

It gets more interesting when you think about the impact on groups. Sending an image to a group is enough for all devices associated with that group to be identifiable from CloudFlare's side, who additionally see a giant chunk of unencrypted traffic from the same client addresses going to other web sites. Given Cloudflare's less-than-straight approach to sales, it is astonishing the words "secure" and "Signal" ever appear in the same sentence.

CloudFlare get to see a fuckton of metadata from private and group chats, enough to trace who originally sends a piece of media (identifiable from its file size), who reads it, when it is is read, who forwards it and to whom. It really doesn't matter that they can't see an image or video, knowing its size upfront or later (for example in response to a law enforcement request) is enough

[lolinder]

> Given Cloudflare's less-than-straight approach to sales, it is astonishing the words "secure" and "Signal" ever appear in the same sentence.

This is an overly binary take. Security is all about threat models, and for most of us the threat model that Signal is solving is "mainstream for-profit apps snoop on the contents of my messages and use them to build an advertising profile". Most of us using it are not using Signal to skirt law enforcement, so our threat model does not include court orders and warrants.

Signal can and should append some noise to the images when encrypted (or better yet, pad them to a set file size as suggested by paulryanrogers in a sibling comment) to mitigate the risks of this attack for those who do have threat models that require it, but for the vast majority of us Signal is just as fit for purpose as we thought it was.

[crawfordcomeaux]

Hello, I'm an organizer for a system to coordinate multiple mutual aid networks, many of which are only organizing by Signal & Protonmail exclusively because they think they're secure and private.

People who are doing work to help people in ways the state tries to prevent (like giving people food) rely on this tech. These are the same groups who were able to mobilize so quickly to respond to the LA fires, but the Red Cross & police worked to shut down.

This impacts the people who are there for you when the state refuses to show up. This impacts the future version of you who needs it.

Most people aren't disabled, yet. Doesn't mean they don't need us building infrastructure for if/when they become disabled.

[hedgedoops2]

Maybe not individual warrants (at least not warrants to do non-scalable collections like hardware bugs in one's phone - I.e. warrants that, most users, with high probability, are not subject to). But mass surveillance, e.g. NSA, even with 'mass warrants' (e.g. Verizon-FISA warrant), that everyone is subject to, is probably in most people's attacker model. I don't have a study handy, but it seems reasonable that most users use signal to protect against mass surveillance and signal advertises itself as being good for this.

Also Marlinspike and Whittaker are quite outspoken about mass surveillance.

If cloudflare can compile a big part of the "who chats with whom" graph, that is a system design defect.

[vel0city]

> Signal can and should append some noise to the images when encrypted (or better yet, pad them to a set file size as suggested by paulryanrogers in a sibling comment) to mitigate the risks of this attack for those who do have threat models that require it

Adding padding to the image wouldn't do anything to stop this "attack". This is just watching which CF datacenters cache the attachment after it gets sent.

[rangestransform]

I think the threat model of enough signal users to matter is nation-state actors, and signal should be secure against those actors by default so that they may hide among the entire signal user population

[doodlebugging]

>It gets more interesting when you think about the impact on groups. Sending an image to a group is enough for all devices associated with that group to be identifiable from CloudFlare's side,

Doesn't this open up the possibility to identify groups that have been infiltrated by spies or similar posers? If you use this method to kinda-sorta locate or identify all the users in your group and one or more of those users ends up being located in a region where you should have no active group members then you may have identified a mole in your network.

Just thinking out loud here since there's no one else home.

[gruez]

>If you use this method to kinda-sorta locate or identify all the users in your group and one or more of those users ends up being located in a region where you should have no active group members then you may have identified a mole in your network.

...unless they happen to be using a VPN for geo-unblocking reasons or whatever.

[paulryanrogers]

I wonder if we'll see assets being padded to some common byte sizes to combat this.

[greysonp]

Hi there, Signal dev here. We do, in fact, pad attachments to a limited set of bucket sizes.

[kijin]

Nothing stops Cloudflare from inspecting the file contents, or using a hash to distinguish between identically-sized files.

The only reason we assume they don't do this is because it's a waste of resources for no good reason. But what if somebody gave them a good reason?

[KennyBlanken]

> , it is astonishing the words "secure" and "Signal" ever appear in the same sentence.

You misspelled "I do not understand what end to end encryption means"