Comment by codedokode | Hacker News Reader

Comment by codedokode | Hacker News Reader

They should only notify users if they both have each other's phone. Otherwise it is trivial to create several thousands of accounts and upload thousands of numbers from each to get a mapping between an id and a phone number. Here is a quote from a head of Russian company that claims to do this:

> A phone number used by [Telegram] account @silovikicat was discovered using a program titled "Insider-Telegram" developed by the "Center of research of legitimacy and political protest". The head of the "Center" Eugene Venediktov explains: "Currently the database contains over 10 million of numbers. We just go through all possible numbers and check whether they are registered in Telegram: for example, we take all numbers starting with a prefix +7911 and check them. You automatically see all contacts from you address book in your Telegram, don't you? We just have a very "fat" address book with phones of all users from our country."

> When a phone number provided by Eugene is added into an address book, Telegram automatically matches it with account @silovikicat («Siloviks' cat»).

Having a phone number means that the government can track its rough location and know owner's identity.

This also means that other messengers using similar contact discovery allow to de-anonymize its users the same way.

[1] (in Russian) https://meduza.io/feature/2019/08/10/kto-takoy-tovarisch-may...

This feature should never have been enabled in this one-way manner but being a social platform means trying everything to get users tied down to it.

It’s just like Venmo. I’m seeing users in my newsfeed because they’re in my contacts but not because we added each other. Really bizarre.

Even better, Telegram should allow to register without a phone numbner (they could charge a little sum in Bitcoins if they are afraid that there will be bot registrations). This could even increase their user base because there are users who don't want to give away a phone number.

Agree, except for Bitcoin (or rather, have Bitcoin but Stripe and other options as well.)

That defeats the purpose, no?

No, only if you are

- fighting someone who controls Stripe well enough to browse transaction logs

- or you are fighting someone who can access your bank transactions (more likely in this case) and manage to correlate them correctly with Telegram account creation time

Both seems like huge steps forward compared to sms validation.

Furthermore: Bitcoin is not much safer for the ordinary citizen. If anything it is way easier to trace than cash and I guess slightly more different to trace than bank transfers.

Or am I missing something?

If you need anonymity you could buy a prepaid VISA

That sounds like the perfect way to test stolen credit cards. In high-risk transactions, Stripe uses SMS 2FA so you're back to needing a SIM card.

Hmmm. Good point if Stripe use 2FA even if it would still be harder for the attacker as they would have to correlate payment - sms - account created - account joined group which is significantly harder to do than what is happening currently.

I guess what they'll do instead is to just outlaw Telegram :-|

> This also means that other messengers using similar contact discovery allow to de-anonymize its users the same way.

While I don't like to have messaging apps tied to the phone number, it has become a mainstream model that most people accept and know how to use.

I have been thinking for some time that we need a mainstream messaging app that uses end-to-end encrypted, and you can get in contact with a peer only if it accepts you (just like old messaging apps, WLM, ICQ, etc), so, if the peer doesn't accept to chat with you, you won't even know whether the number is registered.

In fact, my initial PoC is https://safer.chat/, I just need the time to make an app from it.

Yep, expect no privacy in any app that requires a phone number. At least in most places. More than 150 governments require a proof of identity to purchase a SIM card.

I have a question about Telegram. Let's say I have a number in my contacts, but the other side doesn't have my number in their contacts. So I can now see their name and picture and "last seen"? But can they see the same thing about me without having my number saved? Do they get notified at all? Seems really odd to do this one-way.

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