Oddbean

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 The whole point is that it would be something in your phone contacts, number is most common. Email could work too. I haven’t figured out a decentralized scheme that is private enough yet though 😞

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 Could you do something with 
Hash (pubkey + phone /email)
Generate new pubkey+phone private key.

Sharing that private key would allow friends on nostr to see your pubkey+phone private key.  

Then if receiver of pubkey+phone private key can take normal pubkey+receiver contacts to see if there is a match.  If that key matches any in contacts you could link?

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 The solution will have to piggy back off pubkeys.

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 How are you going to lookup people based on their number with that approach? 🐶🐾🤔

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 If user receives pubkey+phone private key.  They can take pubkey from user + address book to generate private keys and if there is a private key match they know they are friends.  It would require call it pubkeyphone private key for user A to share.  

If user B can take pubkey + any address in contacts, hash it and generate the same pubkeyphone private key and match it to user A they know they are friends.

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 (Phone number share)
User A wants to share phone number. 
Private key of User A is generated using Npub+ phone number.
User A shares that private key.

User B wants to see if they are friends with anyone.
User B takes friend list Npub + phone number list and hashes it (might be lots of random guessing but possible)
If user B generates the same key as user A shared they know they are friends.

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 I think the idea was not to share but to find the npub of your friends who’s phone number you know. 🐶🐾🫡

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 DM'd you

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 Replied 🐶🐾🫡