Should Hive provide "find by phone number" functionality?

[javgh]

This question came up during the Android brainstorming discussion and I am spinning it out into a separate issue here, as it also applies to Hive in general.

Initial idea: Especially on mobile it could be very convenient to find all of your other Hive-using friends by looking them up based on their phone number. This would require us to verify a user's phone number (by sending a text message there) and ask the user if it's ok to go through their address book and look for already verified phone numbers.

Some points raised so far:

• People attracted to Bitcoin are probably often also fairly privacy-conscious, so the feature should be opt-in.
• It's a good idea to hash and salt phone numbers before storing them in some dictionary server, but such a server still offers the whole world a way to find out whether a certain phone number is using Hive. In a naive implementation, where the dictionary server returns exactly one Bitcoin address for a phone number, it would then also allow to look up how much money that person has received so far. An implementation definitely needs to cycle keys or use BIP32 keys or just return some kind of rendezvous point.
• Android permissions can only be requested at installation time. So even if we make phone number verification optional, we still need to request the permission for everybody. We could do without the READ_SMS permission, if we are fine with the user having to manually copy some kind of activation code from his text messages to the Hive app.
• Is phone number verification via text messages safe enough for financial applications? Apps like Whatsapp seem to do fine, but the stakes might be a bit higher here. So would we be running into problems where people manage to intercept text messages and verify other people's phone numbers?
• Possible wording to use: "[x] Let people who already know my email address or phone number find my public address/sync up/whatever"

Additional thoughts?

[mackuba]

I've never had any app ask me to verify my phone number, and I've used "find friends" features many times. E.g. I've tried with Instagram and Foursquare now. Any idea how they might be doing it? Are they only using email addresses? (Email addresses would make sense for e.g. hive-osx, since a Mac address book won't contain many phone numbers, if any, and it doesn't have its own phone number assigned either; on the other hand, using emails only would exclude contacts who only have a phone number, which would probably be more than half of the address book on mobiles...)

[javgh]

My guess would be, that they are indeed either using email addresses (and then verify those in advance with the typical "follow this link" message) or maybe they are using unverified phone numbers, as for some of those services it's not really that critical.

[ghost]

I think the phone number lookup thing is super convenient and something we should do. But I think we should also hash and salt email addresses, etc and thereby utilize whatever local directory the person has to try and find contact matches.

@javgh I trust your privacy-oriented mind will find the best means to ensure privacy/deniability for us and our users, including using peer-to-peer mechanisms and/or the general deletion of any unnecessary data sitting around on servers.

[mackuba]

Related: https://medium.com/p/4791cf1fcf0e

[ghost]

@javgh @mattlenz @mattatgit I'd like to see us implement something like this for ease-of-use, in the most privacy-positive way we can. Can we access system contacts through the Phonegap layer?

[mattatgit]

@w-hive i think the contact system issue is a complex one & we probably need to look at it in more detail than just whether we can access system contacts. Next team call would be a good chance to review next steps & discuss best possible methods for building contacts