TLDR version as per Signal's Mastodon:
Introducing usernames and phone number privacy on Signal!
We’re making it possible for people to connect with each other without having to share phone numbers. Now launching to beta users, available for everyone soon.
- New default: Your phone number will no longer be visible in Signal
- You can create an optional username to connect without sharing your phone number
- You can enable a new, optional privacy setting to require people to connect with you via username instead of phone number
A Signal username isn't the profile name that’s displayed in chats, and isn't visible to the people you chat with on Signal. A username is simply a way to initiate contact on Signal without having to share your phone number. (You still need a phone number to sign up for Signal.)
Create a username by going to your Settings > Profile. Your username must be unique, and can be changed at any time.
To connect with someone via username instead of phone number, type their exact, unique username.
We’re launching these updates to our beta users now, and will be turning them on for everyone running the latest version of the Signal app soon. Our goal is to listen to your feedback, make adjustments, and ensure phone number privacy on Signal is easy and useful for everyone.
You can sign up for beta to test these features. Note that Apple caps the number of iOS beta testers, and we have reached that limit. If you use Signal on iOS, you can get around this by signing up for Desktop beta, linked to your iOS account. See more: https://support.signal.org/hc/en-us/articles/360007318471-Signal-Beta
For more information: Signal's Blog Post
I see this as both a win and a potential problem for the app’s reputation:
As soon as you take away a hard link to a real-life identifier, the sketchy people come out of the woodwork and trade images/video of child exploitation.
Signal has not had this problem like some platforms (e.g. Kik), and I suspect two reasons:
Up until now signal has been an excellent secure replacement for text messaging between parties that know each other. I hope they don’t go the “chat groups” route, though I doubt they will. But I suspect this change will make it a preferred way for abusers to exchange images and videos nearly anonymously
There are anonymous prepaid phone cards. Phone number does not really mean anything.
How would that even be caught in the first place though? It's E2E encrypted so nobody can see what you're posted unless you invite them.
You still require a phone number to register, and your username is associated with that number. It's just the other people you chat to don't get your number - but if you reported a child porn distributor to Signal or law enforcement, they would be able to identify the phone number associated with that username.