When you want a friend to add you on Keychat, you have two options: tell them your QR code or your Npub. We recommend using the QR code because once someone knows your QR code, they can send you messages encrypted with Signal directly, and the QR code is only valid for 24 hours. If you use your Npub, after someone knows your Npub, the first message can only be encrypted with NIP4 or NIP17. Only after they reply can messages be encrypted with Signal.