In case anyone is not aware:
https://news.ycombinator.com/item?id=39444500 Keep your phone number private with Signal usernames (2024-02-20, 1422 points, 890 comments)
https://news.ycombinator.com/item?id=39444500 Keep your phone number private with Signal usernames (2024-02-20, 1422 points, 890 comments)
https://support.signal.org/hc/en-us/articles/6712070553754-P...
"Signal does not send your phone number to anyone unless you have enabled that others can see it and then you send them a message or make a call to them."
https://support.signal.org/hc/en-us/articles/360007061452-Do...
It's something you'd want to avoid if your life, liberty or well-being are at risk if you're de-anonymized.
e-SIM wise, depending on where you are, that might require identifying yourself, and depending on your threat model, having to purchase one in person or with payment info that can be traced back to you might be too risky. Same thing when it comes to using one in a device you own, or in a location that can help de-anonymize you.
In the end, Signal does this because they know the ban hammer would come down hard on them from the Justice Department and every state AG and legislature if Signal allowed bad actors to anonymously use their app and network to commit crimes.
The issue is that there are plenty of people who are not doing heinous things whose security and anonymity might be at risk because of the measure put in place to placate governments.
> the security problem
Think of it this way. There's a vault that's locked with secrets inside, but the door is transparent. This does not prevent privacy. But the vault provides security.
Signal is not a transparent door, but is opaque. You can't see inside the vault. But the phone number reveals that you have access to the vault. This is very different than a security problem. Anyone connecting the two can see that you have a vault (security)[0], but they cannot see inside (privacy) or even when you access it (privacy).
There is no security issue with phone numbers.
[0] or can see that at some point in time you had a vault or someone that previously had that number had a vault
You can also lock registration of your device.
What is your security concern here?
Registration lock expires in seven days or less. [1]
[1]: https://support.signal.org/hc/en-us/articles/360007059792-Si...
> Registration Lock expires after 7 days *of inactivity*
If you use signal once a week you're fine. Maybe it should be longer but that's a different argument and there's no reason to be disingenuous about it
There's a balance they want to strike. You can't assume phone numbers are unique to a person across time. So they need to be able to expire when someone stops using a number.
But again, acting on the other side also gets a notification in the chat stating that the security number has changed. The new person doesn't have the signal chat history. So if you're talking about sensitive things then it's a strong indication you should reverify their identity. Not practical for every day users but that's also not a typical threat scenario
I believe (though I haven't verified it myself) that even if you haven't verified the numbers using an out-of-band exchange mechanism, you will get a warning if the safety number as observed by their server changes. I believe they would need to know your Signal PIN to restore from backup, which means that even if you've set that it will give an alert, presuming basic security competence from the people you are conversing with.
I personally have never seen anyone do this, even when they’re supposed to do it right from the very beginning. So practically this is of very little value to most of the user base.
> Impersonation
You can also do verification of your contacts. Best done in person where you can check the keys.
> MITM attack
It does not
- conclude the user has or even has a signal account
- who that person is talking to
- what that person is talking about
- when those texts or messages are sent or received