Is signal still demonstrating their commitment to my privacy by notifying everyone with my number in their phone contacts who is also on signal when I join ?
Every coach, recruiter, drug dealer or one night stand I’ve had in my life doesn’t need to know when I sign up to Instagram. Some of them might not have even had my real name until they got that notification.
IMO this should be illegal, now that I think about it.
For a government perhaps, but not your average person. This is similar to claiming that my ISP provided IP address is trivially tied to my full name because someone could subpoena it.
Getting name and email and address from phone number is widely available and cheap for anyone.
Still, one has to possess and reveal a valid phone number to use the service. This must help to grow the user base.
It sounds like Signal is trying to solve a different problem than the one you have, so you should probably look for a different solution.
IIRC, Signal's goal is easy to use mass-market E2E encrypted replacement for SMS messaging. If they didn't automatically notify people's contacts, then most of them would probably continue to SMS or use FB messenger, etc.
This form of number is also the one your (mobile) phone actually uses, although they let you type in any sloppy human attempt at a phone number and translate.
Signal apps periodically reach out to Signal's servers to do two things: Confirm that this specific user does still have Signal (and so messages to them should be accepted) and optionally upload a set of these hashes for their contacts to see if any of those have Signal and so messages to those numbers can go securely via Signal instead.
"Hey, add me on telegram, my username is @andrewzah". This isn't a hard problem.
I don't know why we decided apps hoovering up our contact lists in exchange for convenience was so important. For an app that touts itself as private and secure, I still had to explain to my brother why giving it his contact list wasn't a good idea.
I just don't see it as a casual thing the way the target users of these apps apparently do.
I want to explicitly control, per any form of communication, each person who is to be made to know that I operate that form of communication and whether or not that form of communication with me is open to them.
I do not want to open up a new app and have a large populated list of past acquaintances appear, I absolutely do not want to appear in such a list, I would rather not use a given app than risk having someone show up messaging me uninvited.
This is a privacy trade off. Some services chose to keep this list. Signal chose to use phone numbers.
This is very different than Signal doing it automatically when I join.
B. You can exchange identifiers with people whom you want to communicate it just like with any other non-phone-based system: "Hey I'm @username on signal", "Cool, I'm @username2" - composes well with method A.
Solution B ties in to a bigger argument I won't address
the contact prepopulation isn't even that useful. telegram in particular seems to drop notifications if you don't exclude it from power management on Android. if you don't know the user has notifications turned on and has jumped through the hoops to make them actually work, you may as well send messages into a black hole. this is part of why I never assume it's a good way to contact someone without explicitly asking.
I fully understand it is just creepy, and lots of people want the option for this alone.
I'm also wondering if it is to do with notifying people you hope think your number is dead that it is very much alive (people you have ghosted).
Any other reasons? Perhaps this should not just be an option, but an opt-in one.
Every tool has a barrier to use, and even with a strong commitment to security/privacy, Signal seems to have decided that it's more beneficial for their users know which one of their friends are on Signal, than there is potential for abuse. Further, there may come a time where this calculus changes, for example, if spammers arrive on the Signal platform and start decreasing usability.
I feel the reason might be more as a way to promote more widespread use of Signal itself, rather than directly serving their users.
They invented a way to do contact discovery in a secure way: https://signal.org/blog/private-contact-discovery/. From the article:
"Using this service, Signal clients will be able to efficiently and scalably determine whether the contacts in their address book are Signal users without revealing the contacts in their address book to the Signal service."
This is why Signal gets so much benefit of the doubt from the cryptography/security/privacy community. Their default approach to these problems is conservative in favor of the user until they can invent the technology needed to support a feature with security/privacy.
Their solution is to run contact discovery on a DRM Secure Enclave system. Ironic that their privacy solution is to use a technology that privacy advocates say is the spawn of Satan because it hands over control of your machine to Intel.
But I can understand why this is a trade-off they'd make in terms of your comfort level (relatively rare to care about this) vs. massive use-ability and onboarding gains.