NIP-04 defines encrypted direct messages using AES-256-CBC encryption. It was the original method for private messaging on Nostr but has been deprecated in favor of NIP-17 due to significant privacy limitations.

How It Works

Messages use kind 4 events with the following encryption scheme:

  1. A shared secret is generated using ECDH with the recipient’s public key and sender’s private key
  2. The message is encrypted with AES-256-CBC
  3. The ciphertext is base64-encoded with the initialization vector appended
  4. A p tag identifies the recipient’s public key

Security Limitations

NIP-04 has significant privacy shortcomings:

  • Metadata leakage - The sender’s pubkey is publicly visible on every message
  • No sender privacy - Anyone can see who is messaging whom
  • Exact timestamps - Message timing is not randomized
  • Non-standard implementation - Uses only the X coordinate of the ECDH point rather than the standard SHA256 hash

The specification explicitly warns that it “does not go anywhere near the state-of-the-art in encrypted communication.”

Deprecation Status

NIP-04 is deprecated in favor of NIP-17, which uses NIP-59 gift wrapping to hide the sender’s identity. New implementations should use NIP-17 for private messaging.

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