CCN Invitation Event

Signed-off-by: dannym <danny@arx-ccn.com>

kinds/9999 - CCN Invitation.md

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+# Kind 9999: CCN Invitation
+
+## Description
+Kind 9999 is used for invitation codes to join a CCN. This event type facilitates a secure invitation process where a CCN member can generate and broadcast an invitation code that can be used by potential one-time new members to join the network.
+
+## Event Structure
+
+```json
+{
+  "id": "<32-byte hex string>",
+  "pubkey": "<32-byte hex string>",
+  "created_at": <unix timestamp in seconds>,
+  "kind": 9999,
+  "tags": [
+    ["i", "<sha512 hash of the invite code>"]
+  ],
+  "content": "",
+  "sig": "<64-byte hex string>"
+}
+```
+
+## Tag Specifications
+
+| Tag | Value | Description |
+|-----|-------|-------------|
+| i | `<sha512 hash of the invite code>` | The SHA-512 hash of the randomly generated 32-byte invite code |
+
+## Workflow
+
+1. A CCN member generates a random 32-byte invite code
+2. The member broadcasts a kind 9999 event with the SHA-512 hash of the invite code in the "i" tag
+3. The invitee receives the invite code (typically via QR code or direct message)
+4. The invitee generates their nsec (private key)
+5. The invitee sends a direct message to the CCN with their invite code
+6. Upon receipt of a message where the SHA-512 hash matches a valid invite code, the CCN (actioned by the inviter only) broadcasts an accept invite event
+7. The CCN (actioned by the inviter only) sends the CCN seed to the invitee via direct message
+8. The CCN invalidates the used invite code
+
+## Invite Code Format
+
+The invite code is encoded as a bech32m string with the prefix "eveinvite" and contains:
+- The CCN's npub (32 bytes)
+- The random invite code (32 bytes)
+
+## References
+
+* NIP-01: Basic protocol flow description
+* NIP-17: Private Direct Messages