How this app works

NostCard shares contact cards that are encrypted in your browser and published to the Nostr network. There are no accounts and no central server — only you hold the keys.

Getting started

• **Create my card** generates a fresh Nostr identity and encryption key inside your browser. Nothing is sent anywhere yet.
• Fill in your details and press **Save & publish** — the card is encrypted (AES-256-GCM) and published to public Nostr relays.
• Cards are **live**: saving again updates the same card, and every shared link always shows your latest details.
• Your keys are stored only in this browser. Use **Advanced → Backup** to move to another device.

Ways to share a card

• **Share link** — the decryption key is in the #fragment of the URL. Anyone with the full link can view the card in any browser — no app, no account.
• **QR code** — the share dialog shows the link as a scannable QR code.
• **Add-to-contacts link** — opening it downloads the card as a .vcf file straight into the contacts app.
• **In-person pairing** — exchange cards with someone standing next to you (see below).

The technology — Nostr

Nostr is a decentralized messaging protocol. Your card is a signed event (kind 30402) published to public relays — simple servers that anyone can run. This website is just a static interface; the card data lives on the relays.

• **Encryption:** AES-256-GCM via the browser's built-in Web Crypto API. The key never leaves your browser except inside the link's #fragment — which browsers never send to any server.
• **Relays:** they store only ciphertext. A relay operator can see the card name and update timestamps — never your contact details. Avoid full personal names as card names.
• **No lock-in:** because the data lives on the relays and the key in the link, a card can be opened from any deployment of this app — even one hosted on localhost.
• **Deletion is best-effort:** deleting a card sends a NIP-09 deletion request. Well-behaved relays comply, but an archived relay may keep a copy — this is a property of all public relays.

Trust models

When someone opens a card link, the app first asks where they are. The answer controls what is stored on that device.

• **My personal device** — the link is saved locally for quick access and the device is remembered for 30 days. Bookmarking is encouraged and downloading the contact as a .vcf is allowed.
• **Shared or public computer** — nothing is saved. The session auto-clears when the tab is hidden, after 5 minutes, or on "Done". Downloading is disabled.
• **The link is the password** — anyone holding the full link can read the card. For extra safety, send the base link and the #key part through two different channels (e.g. email + Signal).

In-person pairing (Connect)

**+ Connect** starts a mutual exchange: you get a QR code, the other person scans it, and you each pick which of your cards to share. Both cards end up saved under Contacts. The pairing code expires after 30 minutes and the exchange runs over the relays as an encrypted handshake — only accept when the person is actually in front of you.

Controlling your data

• **Rotate key** — generates a new encryption key and re-publishes the card. All previous share links stop working immediately.
• **Delete card** — removes the card from this device and sends a deletion request to all relays (best-effort).
• **Verify privacy** — the editor's privacy proof shows exactly what a relay can see versus what the key unlocks.

Backup and sync

• **Backup** exports a JSON file containing everything, including your private keys. Anyone with that file controls your cards — store it securely.
• **Sync** publishes an encrypted snapshot of your cards to your relays using a passphrase. Enter the same passphrase on another device to pull it in — anyone with the passphrase can read and overwrite the snapshot, so keep it secret.