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Comment by viktorcode | Hacker News Reader

So far the biggest weakness of Signal is identification via a phone number. It's not only hackers who can spoof the numbers, but an authoritarian governments too may take ownership of a number at any moment.

Addressing future threats is good, but priorities should be different.

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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)

This is different though. PP is saying that you require a phone number to sign up, and phone numbers are being used to match your account to your user name.

Agreed as far as governments tracking Signal sign-ups. For a long time though user names were not even supported between Signal users.

"As a new default, your phone number will no longer be visible to everyone in Signal."

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...

This doesn't address the security problem

  > the security problem

You're confusing privacy with security. Phone numbers are a privacy problem and NOT a 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

Is there not a security problem if your phone number is seized? I don't need excuses about the likelihood of the threat model.

If your number is seized then the new account holder has no chat history. i.e. the vault is cleared out. In that situation you will also be kicked out, clearly telling you that your account has been hijacked.

You can also lock registration of your device.

What is your security concern here?

Impersonation, MITM attack

If you have done the out-of-band safety number verification, then impersonation attempts will give you a warning that their safety number has changed. I know this because I got that error when my wife replaced her cell phone.

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.

> If you have done the out-of-band safety number verification

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.

You get notifications if the safety number gets changed from a device change either way. But doing the in person validation helps ensure that particular safety number you received was actually their safety number and not a MitM on first contact.

  > Impersonation

Yes, but with a canary. Would you rather not have a canary? The other person also receives a warning that the verification number has changed. It's not like the existence of a phone number is what creates the ability to hijack an account. And again, you can do registration locking so that solves that problem.

You can also do verification of your contacts. Best done in person where you can check the keys.

  > MITM attack

I don't think that means what you think it means. Who is in the middle? This is E2EE

> You can also lock registration of your device

Registration lock expires in seven days or less. [1]

[1]: https://support.signal.org/hc/en-us/articles/360007059792-Si...

Please actually read

  > Registration Lock expires after 7 days *of inactivity*

I don't know why you dropped "of inactivity" and changed it to "or less".

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

It does not matter if you lose control of the number, the new person will be able to register. The 7 days period is for you to get control of the number back or make sure all your contacts know about the issue.

am I reading it wrong? but on my phone if i activate reglock again it says that if pin fails the account is blocked for seven days. I asume that after 7 days one still needs the pin to register or am i wrong?

You'll get the opportunity to change the pin.

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

Seems like you missed reading the entire context above. The discussion was about a number being seized or taken over by someone else. So your reply on inactivity is irrelevant since the new owner of the number can just wait a mere week and use it with Signal.

for this reason there is the signal pin. they need pin and phonenumber to hijack the account. afaik

A lack of privacy is a security problem for messaging. A lack of privacy predisposes some people to rubber hose cryptanalysis by the authorities.

The privacy loss is "phone number has registered a signal account"

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

What can you infer here that becomes a security risk? I guess if signal is outlawed before you have installed or your number was ever associated with an account? But it still have plausible deniability there

Neither of these are the issue, the issue is the required association of a phone number with a Signal account. You cannot register a Signal account without a phone number.

It's something you'd want to avoid if your life, liberty or well-being are at risk if you're de-anonymized.

Realistically could use an e-sim or text verification service to sign up.

Signal, like most services, block text verification services, free texting apps, etc.

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.

Google Voice worked for me a few years ago

This entire post does not follow

Many other secure IM software managed to work without phone numbers and they are also metadata resistant. Signal should start doing things that way.

In many countries your SIM card is tied to you, which is a huge deal-breaker.

Yup, in Poland, a mobile phone number (pre-paid or not, it doesn't matter) is tied to a PESEL number [1] at the time of purchase. The official justification, as usual, was combating crime, but the end result is a tighter grip on citizens' privacy by the government while spammers and others continue their business as usual.

[1] https://en.wikipedia.org/wiki/PESEL

Same or similar in Germany. Almost impossible to get a SIM card without showing up somewhere with your id. Or I don't know how to.

Just step into a random supermarket in a neighbouring countr and buy a SIM in cash at the register.

It's crazy how heterogeneous rules are inside the EU.

Its a difficult problem because you, ideally, want to curb spam. Requiring phone numbers is a somewhat easy and somewhat reliable way to do that.

Sort of. There are now immense warehouses filled with racks of used cell phones to generate spam. Limiting by phone number helps, but it's FAR from being an adequate cure.

Yeah, if the telegram and whatsapp spam I get is any reading, limiting by phone number is not sufficient.

whatsapp is the worst because it shows everyone the phone number

If no one knows your user ID besides you and the people you share it with, why would spam be a big issue? If it's a random string, I don't know how anyone could get it, unless you share it publicly or with someone untrustworthy who shares it publicly. And even if it's a username users choose, as long as there's no directory it still shouldn't be a big problem.

That is - even if someone makes 1000 bot Signal accounts, what can they really do with that if they don't have a good way of enumerating other Signal users?

  > if they don't have a good way of enumerating other Signal users?

You can always brute force.

Btw, if you don't accept message requests from spammers they have no indication of if you have an account or not. Try sending a message to a friend who you haven't added on signal. You can just see you sent the message but not if it was received or rejected or anything. Not until they click accept

If it's a sufficiently long random string, that shouldn't be possible, right? Admittedly not an amazing user experience to have to share a random string to your friends, but many Signal-like apps do this.

Great point that requiring a friend request beforehand kind of eliminates the issue too. I assume the Signal developers do have a good reason for thinking requiring phone numbers reduces abuse, but I'm having trouble understanding it.

  > Admittedly not an amazing user experience to have to share a random string to your friends

And struggle to get adoption. If it's too long, it's hard to share but difficult to brute force even with massive parallelism. But you can always brute force, it is just about how effective brute force is. Entropy is a double edged sword.

It's also harder to then do contact discovery to find who's already in the network. Which is the basic principle of any social network (yes, I'm calling old school landline phones a social network too). It's a tradeoff, right?

And it's worth noting that usernames exist now and this is serving as a bridge. You can provide links and QR codes too. I think this is a fair system and allows my grandma to use signal while still providing a path forward to another paradigm.

This brings me to one of my critiques of signal. I wish they would recognize we all have multiple identities. My real name obviously isn't godelski. But I might want to link my contact here on HN but not reveal to those people that my actual name is "Joe Schmoe". We don't need unlimited identities but having 2 or 3 could really do a lot for privacy. Let me have a little more granularity over my privacy settings. Let me have some people contact me via godelski.## and some by joeschmoe.##. The former sees my name as "godelski" and the latter as "joe".

And to be clear, the phone number issue is privacy related, not security.

> not an amazing user experience to have to share a random string to your friends

It doesn't have to be that way, at least in theory.

They can nerf accounts without verified phone numbers to be unable to reach verified accounts. And delete idle unverified accounts sooner, to combat potential DOS.

People who believe their phone number will be used to deanonymize them, can just use an account they keep unverified, and exchange IDs via other channels. It's harder, but for these people it will be worth it.

The rest of us can verify our phone numbers, and enjoy the easy discovery. (The way it is now.)

Machine-created, unverified, spam accounts will have to brute-force address space way bigger than that of phone numbers, and still only be able to reach other spam accounts, or an occasional very privacy-sensitive user.

I have no idea whether the above is technically possible, though.

You can't brute force it if the ID is large enough. E.g. if it's a 256 bit ID, sending 10^18 brute force messages per second it would still take 10^41 years until you hit a real user (assuming 6 billion users).

"Can I contact you on signal? Just wait for a few minutes while I type this 64 character long hex string".

I know you can work around this with QRs, but that's poor UX, has many failure scenarios and takes a long time. In comparison, you can just tell someone your phone number, even without neither of you having a phone nearby - you just need a piece of paper and a pen.

Signal brought security and privacy for the masses, because it - correctly - prioritized ease of use over tech-nerd paranoia.

  > but that's poor UX, has many failure scenarios and takes a long time.

And requires you to build your social graph from scratch. That alone is killer to the average person.

Is signal the right tool for those hyper concerned with both security and privacy? No. But is it the right tool for the average person to securely communicate and get some good privacy? Absolutely.

People forget the GPG days. GPG had a huge flaw back then: you can't send GPG encrypted emails if no one was going to read them. It didn't become viable until that part was hidden in the background.

It's even easier than that since you already have the phone numbers in your contact list, they will just show up as soon as you sign up.

Good luck brute force guessing an Ed25519 keys (32 bytes).

Honestly there are so many better options than phone numbers available. If you're already using QR-codes to transmit user ids, you might as well use something that is transferable and user generated.

You're reading the problem wrong. Yeah, even considering the birthday problem you're going to have a hard time finding a valid key.

But now we have a discovery problem. How do I find my current contacts? Do I need you rebuild my social graph from scratch? Good luck getting my friends with PhDs in computer science doing this, let alone my grandma.

Entropy is a double edged sword. IMO signal is doing a good job here. We can go drop phone numbers completely when enough people are using signal. But while the userbase is low it's probably worth the 3 spam messages I get a year. I get more than that in a week on my iPhone and more than that a month when I used Android. So I'll take the trade.

And I must stress, the phone number issue is about privacy, not security. At least with regards to signal

One can still use simpler contact information like a phone number, email or QR code to transfer a user id.

While I love what Signal has done, the compromises are significant. I use Secure Scuttlebutt, Cabal, Spritely Goblins, Tor, email and a variety of other P2P software on whatever device I like, but Signal requires a phone with Android or Apple, and requires that I lock my id to my phone number.

  > the compromises are significant.
  >  I use Secure Scuttlebutt, Cabal, Spritely Goblins, Tor,

And which of those are you able to communicate with your grandma on?

Honestly, I don't care how secure or how private (phone numbers are a privacy issue, not a security issue) if I have no one to communicate with. You need to solve the mass adoption problem.

You know Signal is doing something right when even the constant doubters use it. Exactly because it's very accessible.

There are always compromises some of them are hard to make. Signal successfully makes private / secures the “normal” conversations that would otherwise be on some Facebook owned app. None of the alternatives manage to do that.

Once you get Signal messages from randos without fist contact. Like airbnb hosts with password codes or IT admins or lawyers… it makes clear that they are doin it right.

Honestly it's just shame the platforms won't allow them to be the “native” sms app like iMessage. That would be the most ideal and probably upset much of the police deparments.

It's always the same complaints and they are trivial. Phone numbers, onboarding is hard because capatcha (wtf?!), signal is pwned because they got money from a government grant, moxie did some weekend hacking to integrate a cryptocurrency and so it's all shit.

I've never understood these. Even the non conspiracy stuff is just... nothing. Like do what? That's a roadblock for you? Then you shouldn't be on HN or be using a phone in the first place. Best to get off the internet all together.

I just don't understand why there's so much passionate hate. It feels like bots and trolls running a disinformation campaign but I actually think it's real people

Perfect is the enemy of good.

It's sad because the people who are doubting tradeoffs Signal deliberately made don't seem to realize that it's these tradeoffs that make Signal work. They also usually don't offer any good faith critique, answers or solutions.

In signal you can change your username any time.

Bots join group chats to scrape user lists to spam. It's also desirable for users to be able to find their contacts already on Signal with phone numbers.

Replace "user ID" with "email address". Pretty much the same thing. But spam is a huge problem with email.

But people use their emails for more than just talking to people. You don't need an IM account to, say, register on a website.

Whitelisting solves spam. Phone numbers should be obsolete by now.

You don't need phonenumbers to deal with spam, just set the "allow messages only from contacts/friends" and a way to add new contacts when needed (via username, email, or even a phone number). It used to work without issues with protocols like MSN messenger, aim, icq etc.

This, exactly this.

I don't want everyone who knows my number to be just able to reach me.

Whitelist instead of Blacklist!

Nowadays this is a premium feature and you have to pay for it

You can set a password in Signal, preventing movement of your account in case of SIM hijacking. Feature is called "Registration lock".

  > identification via a phone number.

Identification of what? That you have a signal account?[0] I'll admit that that's not ideal but I'm unconvinced this is a big issue.

  > an authoritarian governments too may take ownership of a number at any moment.

Suppose they did hijack the account. This would not give them the message history. You know that, right? It also kicks out the original owner, warning them they've been pwned.

Don't get me wrong, Signal has issues and we should be critical and hold them to high standards. BUT *they are only E2EE and low metadata Messenger that my grandma can use.* That's a big fucking deal. If we want secure communication to be common place we need to make sure it's usable. Sure, there's more secure and more private services, but none that my grandma could use.

I very much think signal should shift focus to privacy as they've got the security side pretty well handled (as this blog illustrates). But also these comments at the top of any signal thread feel a bit out of touch. Maybe I'm reading too much into it but there's a lot of people who confidently act like this compromises security or places harm on a user. The existence of a registered signal account means very little, especially as you note numbers can be spoofed. You need more than a number to hijack an account and hijacking only reveals messages moving forward while telling the compromised user they're compromised.

So can we focus on bigger issues? Can we critique while still recommending? I have no problem saying I have issues with signal and wish they did more while acknowledging that it is strongly my preferred means of contact and I try to convince others to talk to me that way. These things are not at odds. I've gone so far as donating to them several times because I use the service so much

[0] https://signal.org/bigbrother/

Imagine being someone who would downvote this without a comment.

Is it:

"I disagree but am not literate enough to state why"

Or is it:

"This person is right, but I don't want people to know it (insert motive here), so I will try to make their comment invisible"

Either way they're cowards, and you are correct. Signal is the best intersection of genuine security and ease-of-use I've seen.

My points are positive now but the variance has been huge. I'm surprised how often a comment like mine swings or gets entirely downvoted without a reply. I do not know if it is zealots, bots, or people just feel like the issue is "so obvious" that it needs no addressing. But I'm not sure how that's different than the first item.

It is also crazy to see how on HN of all places there's still a lot of confusion between the difference of privacy and security. People are saying phone numbers are a security issue. That's flat out wrong. It is a privacy issue.

Having run some family through the Signal onboarding process lately I'm actually kind of disappointed though: the CAPTCHA requirements are a big turn off, and it was relatively difficult to get them to see "look I'm on Signal!" In their existing contacts.

To wit: phone numbers have to stay. That's how I even get people to use it with me, and that's enormously valuable.

But also: there really needs to be a way I can use my own account to vouch for a new user and skip that CAPTCHA (maybe there is? What happens if I do an in app invite?)

Except Captcha is to make it harder for spammers, if they just have to do Captcha once and then invite more accounts it kinda defeats the purpose.

Yeah the onboarding process isn't the best but... is CAPTCHA requirements really that big of a deal? Where on the internet can you go where you don't face these? Maybe my grandma can't handle that, but my already retired parents can (and that's a pretty low bar if you know them). For my grandma, yeah, I'll set it up. For my parents and anyone under 70 I think CAPATCHA is not too high of a bar.

I think your threshold is too high. How high off the floor is a CAPATCHA? Because it looks like a bar rolling on the ground to me. You can trip over it but it is almost trivial to get over.

If I invite someone to use Signal and I'm not physically in the room with them, then what should happen is I get the CAPTCHA challenge and they get the magic link which avoids it.

They can take ownership of the number but not the keys on the device, which would show up as safety codes changing.

This problem is honestly minor compared to teaching users to have opsec practices suitable against such a threat.

Most people take no notice of this stuff IMO. I see it regularly in WhatsApp groups when someone gets a new phone (presumably, or they are being impersonated!).

Right but thats my point: if you adversary is a nation-state, assuming any technical measure can casually protect users against targeted action is foolhardy.

Check molly, FOSS Implementation of signal protocol

https://molly.im/

That's a fork of signal.

Also annoying: You cannot use the same Signal account from 2 different phones (with different SIM).

It's pathetic, isn't it?

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