Add NIP-144: Service Authorization Protocol

[btcjt]

Summary

• Introduces NIP-144, a protocol for authorizing third-party services to interact with a user's Nostr data without exposing their private key (nsec)
• Defines a shared symmetric encryption key workflow between a principal (user) and a service, where the principal retains full control over authorization, key rotation, and revocation
• The shared key grants encryption/decryption capability only — no signing authority — so a compromised service cannot impersonate the user

Motivation

Nostr-native applications increasingly need server-side services to handle sensitive data (payment credentials, encrypted configuration, etc.) on behalf of users. Sharing an nsec is unacceptable: it grants full signing authority, cannot be selectively revoked, and a single service compromise exposes every user. NIP-144 solves this with scoped, rotatable, revocable shared keys.

Design

• Kind 31440 (Service Authorization): Addressable event published by the principal. Contains the shared key encrypted via NIP-44 ECDH to the service's pubkey. Supports optional a tag scoping to bind authorization to specific entities/datasets.
• Kind 31441 (Service Authorization Acknowledgment): Addressable event published by the service confirming receipt. Contains a SHA-256 hash of the shared key as proof of possession.
• Encryption format: Reuses NIP-44 v2 primitives (ChaCha20 + HMAC-SHA256 + HKDF) with the shared key used directly as conversation_key — no new cryptographic constructions.
• Rotation: Principal publishes a new kind 31440 with the same d tag (addressable replacement).
• Revocation: Kind 5 deletion or expired replacement; service must purge the key and delete its acknowledgment.
• Optional NIP-98 notification: Principal can HTTP-notify the service of a new authorization for immediate pickup rather than waiting on relay subscriptions.

Test plan

• Review NIP-144 spec for completeness and consistency with existing NIPs (especially NIP-44, NIP-46, NIP-98)
• Verify event kind numbers 31440/31441 do not conflict with existing allocations
• Validate encryption format description matches NIP-44 v2 primitives
• Review security considerations section for completeness