Or in other words: suppose the definition of "phone number" was expanded to include alphanumeric characters and @. What aspect of Signal's current design would break? By saying "without phone numbers, they can't use clientside contact lists", you seem to be suggesting that something would break, but I can't imagine how, unless it's as trivial as a database constraint that says "this field must contain only digits".

I feel like you're mis-analyzing a social problem or some other design goal as a low-level technical problem.

I don't know their real reason, but I can say that my email contact list is waaay messier and less curated than my phone contact list. It would probably be annoying is I'd get a "So-and-so joined Signal!" notification for a bunch of randos I've emailed once and had their email auto-added to my address book.

I'm mostly just confused because this is being presented as a technical limitation: using email addresses would supposedly "require Signal to keep a database of contacts serverside". I don't understand how or why that's true.

I don't know what the real reason is, what I said was just something that popped into my head. Another comment mentioned spam-prevention as a reason (by making it infeasibly expensive), and that actually makes more sense. Honestly, there probably isn't just one reason, but a cluster of tradeoffs.

> Isn't it better to have a larger pool of people with whom I can communicate securely using Signal?

IMHO, the number people who care deeply enough about the phone number thing to boycott Signal is vanishingly small; not even a rounding error. Sure they're loud on HN or maybe even Twitter, but giving tiny but loud minorities whatever they demand is bad policy.

What I meant was: "it's better if I can use Signal to communicate with people even if all I know is their email address".

One of the reasons I wish I could use something other than my phone number and access to my contact list to work with signal is these notifications creep me the fuck out and I would rather never get them, or have anyone get them about me.

I'm fine with it being a feature for people who want it, but I don't. I want to make my own damn choices about who I talk to through it.

OS functionality? There no "Grant access to Gmail contacts" (= email addresses) on Android/iOS, so that client-side list would have to be manually maintained, while (practically) everyone already has a contact list containing phone numbers of their friends.

That said I don't see why a user would have to have a stored social network at all, why can't it simply be opt-out?

But this is all moot because phone numbers aren't just opaque binary strings. They are more useful than other forms of identification.

Addendum: also, there is nothing preventing this type of contact book data from being backed-up/synced to a new phone, like any other data and settings of any other app. iOS has this feature since like 7 years now. Android, too, I'm sure.

How do you transmit said anonymous user token securely? Using the secure messaging app you're already using? Meeting up in real life? Posting it on keybase? Each of these has downsides that are all solved by a phone number.

I regularly DM people I haven't seen in person in years. I'm not going to fly cross-country to bootstrap a communication channel.

> or exchanging account names in whatever way you initially exchanged phone numbers?

Well because I exchanged phone numbers irl 7 years ago. I do not have a time machine.

> You don't seem concerned over the security problem of account activation codes being sent over SMS, so I don't see why you should be concerned over exchanging anonymous account names in the same or more secure ways.

Correct, because the bit of information "I have a signal account" is far less revealing than the bit of information "I have shared my signal account with a particular individual".

You avoid that only with some kind of public attestation of your signal identity (in keybase or on twitter or whatever) which is the best option, but generally requires everyone have a known public index of their forms of contact, which my friends from high school, generally speaking, don't.

(I still consider it a major downside that the phone number is the only lookup key)

I don't understand why you state this, when you obvioulsy know that data is connectable and joinable across discrete sources. Being "the only social network available to service X" is the inherent case for every single online service on the entire planet when viewed as an isolated entity. But this isn't a case of anonymized UUIDs. It's a case of personal phone numbers.

Apart from using the device contact list (which contains email addresses as well as phone numbers) the client can also keep a private contact list.

E-mail as a complement should work fine and supported in all contact lists. It wouldn't change a thing wrt what you're describing.