Nostr sign-in (NIP-07)

Use this skill for authentication only — signing sign-in events that prove ownership of a Nostr identity. It never publishes notes, connects to relays beyond the configured callback, or requires a wallet or browser extension.

Inputs

• A sign-in challenge from a "Sign in with Nostr" page or API — either an event template (kind, tags, content) or a challenge string.
• Optional --domain for the service host (used for deterministic key derivation), --callback URL to submit the signed event to.
• Optional --dry-run when the signed event must be inspected before submission.

Do not invent or alter challenges. Ask for a fresh challenge when the service reports it was already used.

Run

The bundled helper uses only Node.js built-ins and lives at:

<skill_dir>/scripts/nostr_auth.js

Inspect the identity and signature without authenticating:

node <skill_dir>/scripts/nostr_auth.js pubkey --domain example.com
node <skill_dir>/scripts/nostr_auth.js --challenge "<hex>" --relay "wss://..." --dry-run --json

After confirming the service and callback are expected, submit:

node <skill_dir>/scripts/nostr_auth.js --challenge "<hex>" --relay "wss://..." --callback "https://example.com/verify" --json

Or sign a full event template:

node <skill_dir>/scripts/nostr_auth.js sign '{"kind":22242,"tags":[["challenge","<hex>"]],"content":""}' --domain example.com --callback https://example.com/verify --json

The helper requires Node.js 20.19 or newer. The only network request is the final callback POST.

Protocol

1. Derive a per-service secp256k1 private key: HMAC-SHA256(master, domain), from the persisted master secret (~/.config/nostr-auth/master.key, mode 0600).
2. Build the event (kind 22242 for challenges by default), compute the NIP-01 id sha256(JSON.stringify([0, pubkey, created_at, kind, tags, content])).
3. Sign the raw 32-byte id with BIP-340 schnorr; store the 64-byte signature as hex in event.sig.
4. POST {"event": <signed>} to the callback. Interpret {"status":"OK"} as accepted; a fresh challenge is needed after {"status":"ERROR"}.

Identity and safety

• Keep the master secret local (0600); expose the nsec to nobody.
• Per-domain derivation keeps unrelated services from correlating identity.
• Inspect the callback URL and signed event in --dry-run before submitting.
• The npub derived here is an agent identity — it is not the same key as a user's browser extension unless the master secret comes from it.

Failure handling

• Invalid hex / odd length — malformed key or challenge input.
• Callback returned non-JSON or HTTP <n> — the service is down or the URL is wrong; verify --callback.
• {"status":"ERROR"} — challenge may already be used; request a fresh one.

Self-test (offline, cost-free)

cd <skill_dir>
npm test

The local mock service validates the full sign → submit → verify roundtrip.