Phone numbers are the most identifying piece of information. They are precise identifiers not pseudo-anonymous. A non-burner phone can easily be converted to a complete background check on the person for under $50 ,for a higher price it can be converted to current realtime physical address.

> easily be converted

Could you link to a reputable resource for this? I've always imagined that phone number background checks were mostly scams with a bit of public information sprinkled on top.

I'd be very surprised to learn that I could purchase a burner phone, give you the phone number, and have you be able to tell me my address and criminal history.

They just said "non-burner phone."

> I'd be very surprised to learn that I could purchase a burner phone, give you the phone number, and have you be able to tell me my address and criminal history.

OK, so even if you pay cash, there's video surveillance in the store, and surveillance (license tag, video, etc) on the route. And that's linked to the number. Then there's the number that you call from to activate the burner phone account, which may have some identity information. Plus geolocation data for that, and for the burner phone.

When I was living in Brazil to buy any kind of SIM card you had to give your CPF or whatever it was called number from your residency card. I believe many countries have this rule as coiner terrorism measure or whatever. Of course for bad guys it’s trivial to go around those restrictions.

And that's a near best case scenario in the US, UK, etc. In most of Europe and many other countries, you have to officially register a SIM card with an ID/residence document to use it.

Huh. Is that more or less recent?

I guess that I'm a few years out of touch.

There's no ID requirement in the US, I think.

Right, I meant that the scenario described is a near-best case in a global context as many (most?) countries unlike the US/UK/etc. require ID verification.

No legal requirements, hence burners. But as a rule carriers enforce it.

I don't believe this is true. It's very trivial to find a prepaid SIM in the US that one can just purchase, activate, and top-up with reload cards (which in turn can also be purchased with cash). Postpaid plans do often require ID verification because of the credit that is being extended, which I think is more than reasonable.

For non-burner phones, just Google the phone number---you'll probably get a sketchy "look this person up for $XX.YY" telephone directory page that will contain their full name and age, if not their address.

So, I just Googled my phone number, and the phone numbers of several friends.

In each case I got dozens of the same flavour of site, which I've seen many times before, it has a paginated list of every possible phone number that could exist, and an advertisement. These sites are pretty cheap to build and presumably over their lifetime they bring in enough advertising revenue to justify renewal costs, hosting and so on.

But they don't offer (and couldn't deliver) personal information about any of us, since that isn't publicly available.

At any rate all of this misses the point; Signal doesn't use phone numbers because phone numbers are an especially good identifier, but as a UX tradeoff to keep metadata off their servers.

I have good reason to believe this UX "tradeoff" is being actively abused. Several vectors,but the main one has to do with contacts of a compromised target,or when a target adds you as contact.

In practice,it's worse than having to use your SSN. You don't need SSN to sign up with all the major apps and sites (including free email),but you do need a phone#.

Can you go into a little more detail (or link me somewhere that does)?

This sounds like an interesting trade off, but I'm not totally following how using phone numbers and contacts avoids the metadata on server issue.

I think it boils down to the fact that in Signal the server can't see which conversation messages belong to - and if sealed sender (aka secret sender) is enabled, the server can't see who they're from. (As far as I know, the server still tracks the phone number of accounts and thus the recipients though - looking at https://github.com/signalapp/Signal-Server/blob/2b987e6e9301...)

Unsure how this relates to contact lists though (other than that secret sender is apparently only available for messages from people in your contact list?)

Matrix on the other hand isn't a message-passing system like Signal (or IRC or XMPP or SMTP) - instead it's a way of securely storing your conversations (more like NNTP or IMAP). This means that when you log into a new Matrix client you can get at your conversation history, and it means that even if you lose all your clients you don't lose your history.

The compromise is that Matrix ends up storing the metadata of who spoke to when in the conversation history which is stored on the server.

However, we're working on mitigating this with P2P Matrix (where you run the server clientside, unless you explicitly want to pin that conversation to a serverside server), as per https://fosdem.org/2020/schedule/event/dip_p2p_matrix/ - and it even works :)

Did you pay? At least in the U.S., states release ridiculous amounts of information on people. It's "publicly available", but in practice states charge a high fee for the databases, which means most of this data exists behind paywalls. The data on sites like spokeo.com and intelius.com isn't great--not at all comparable to the breadth and quality of data LexisNexis offers with their 5- and 6-figure subscriptions--but it's amazing how many phone numbers, names, and addresses you can still match up.

Then there's all the "private" data about you that is commercially available. That's what credit agencies and similar companies do--buy your data from any company willing to sell it. Such databases are so deep and comprehensive that these companies have become extensions of intelligence organizations for all the business they do with government. In fact, just a year or two ago there was the "scandal" where it turned out cellphone companies were selling location data, which some savvy police departments started using to avoid dealing with warrants.

I said a non-burner phone

Signal's servers store no contact lists at all. It's not that phone numbers are some especially good anonymizing identifier; obviously, they are if anything the opposite. It's that everyone who uses Signal already has a local contact list keyed on phone numbers, which Signal's client applications can access, which means the server doesn't have to know about contact lists in the first place.

> It's that everyone who uses Signal already has a local contact list keyed on phone numbers ...

Well, that's precisely why I don't use Signal. In that I don't use smartphones. I could probably run Signal in an Android VM. But I have no way to get a phone number that's both adequately anonymous and adequately secure. Or at least, I don't yet know how to do that. Burner phones are too readily located, and hosted SIMs are too insecure.

Android x86 VMs now have functional virtual WiFi interfaces. But I'm not aware of a virtual cellular network implementation, which could theoretically (I imagine) allow virtual SIMs. That would be very cool. Or maybe it's doable with VoIP?

But this ostensible "Signal's servers store no contact lists at all" policy also incurs several serious risks:

* The Signal client regularly re-sends your complete local contact phone numbers to the Intel SGX contact-intersection code on Signal servers. So, potential flaws in that process would mean Signal servers continually receive, & could possibly log, far more metadata than competing systems that upload all your contacts' phone numbers.

* Signal leaks that your phone number has enrolled with the Signal service to anyone who chooses to query it.

You are comparing the possibility that something could go wrong and expose contact graphs to systems in which exposure of the contact graph is a foregone conclusion, because the servers store them, durably, online, in plaintext. The point of the Signal design is not having to do that thing, and, indeed, it doesn't, unlike other secure messengers that do.

No, I'm comparing Signal to desirable properties of a secure messenger for many important uses.

It's great that Signal has devised a system that, ostensibly, obviates the need for them to keep persistent lists of everyone's correspondents. But as that same system requires the constant, repeated uploading of phone-number-identifiers, and complete trust in Intel SGX™, it misses the primary thing most want from an end-to-end, open-source solution: no reliance on remote personnel or systems.

Signal's created a fancy 'Maginot Line' that ultimately reduces to the same core flaw as much-simpler architectures: if a small number of hard-to-monitor key people or servers are compromised, even temporarily, the metadata is also compromised.

You tout that "Signal's servers store no contact lists at all". But can you prove that? Signal's servers are still sent all the same data that would be required to do that.

Meanwhile, other secure messengers manage to:

* avoid ever knowing a users' phone number, or revealing a users' phone number to their correspondents

* avoid broadcasting the fact of a user's participation to anyone who cares to query

It's important to remember these caveats & tradeoffs when alleging Signal stores no contact lists at all.

Again: your argument is that, because someone at Signal could misbehave and log metadata, Signal is equivalent to systems that log metadata all the time, durably, by design. Given the choice, I'll take the system that can at least plausibly protect my metadata over the one literally premised on not doing that.

I'm not alleging 'equivalence', I'm emphasizing assumptions & tradeoffs.

I want readers to know that your headline claim, "Signal's servers store no contact lists at all", should be coupled with the important caveat that believing that claim still requires trust in Signal and Intel personnel/servers.

And even if someone, like yourself, assumes such trust in Signal & Intel, the metadata protection Signal does offer still requires other metadata tradeoffs. That's not 'equivalent' to other options, it's different in notable ways. For some users, like say an anonymous whistleblower without a 'burner' phone number, Signal's metadata handling is arguably worse than other extant options.

You find Signal a preferable, perhaps even dominant choice; I think they're a mixed-bag once aware of all the tradeoffs.