Adding a contact and exchanging data

To issue a bill to someone, or endorse one to them, you need their node id. Adding them as a contact is how you get it and keep it.

Resolving a contact

A contact is added by node id. Because a node id contains the participant's Secp256k1 public key, and their Nostr npub is derived from that same key, a node id is all that is needed to find them: the client resolves the npub, looks up the relay list that identity publishes, and reads their public profile data from there.

No handshake and no approval step is involved in finding someone. Their public data is public.

Sharing your own details

Publishing works the other way round, and with one restriction worth knowing: a client will only publish contact data for a node id it holds the keys for. You can publish yourself; you cannot publish somebody else.

Private contact information

Public profile data is the small part. The fields on an identity record, such as postal address, date and place of birth, identification number and identity documents, are not broadcast.

Sharing those is a deliberate act, and it works by sharing derived keys over a private message. Rather than sending the data itself, the client sends the keys that decrypt it. Two consequences:

• The recipient can read what those keys unlock, and nothing else.
• The data does not have to be re-sent when it changes.

This is the same idea as sharing a bill: pass the ability to read, not a copy.

Why a contact is needed before a bill

A bill names its parties by node id, and the drawer and drawee must be identified parties rather than anonymous ones. So issuing a bill to a counterparty means already knowing who they are in the protocol's terms.

The practical order is: add the contact, exchange whatever private details the trade requires, then issue.

Companies

A company is addressed by a node id in exactly the same format as a person, and is added as a contact the same way. What differs is the record behind it, and that a client can act as either a person or a company, switching between the identities it holds.