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Kind 13: Seal ​

Overview ​

Seal events (kind 13) are part of the Gift Wrap protocol (NIP-59) used to encapsulate and encrypt Nostr events. A Seal wraps an unsigned event (called a "rumor") and is signed by the true author of the content, but with the content encrypted to hide it from third parties.

Specification ​

PropertyValue
Kind Number13
Event RangeRegular
Defined inNIP-59

Content Format ​

The content field contains an encrypted "rumor" (an unsigned event). The encryption is done using NIP-44 versioned encryption with a conversation key derived from the sender's private key and the recipient's public key.

Schema ​

json
"content": "<encrypted-rumor-using-nip44>"

Tags ​

Tag NameDescriptionFormatRequired
NoneSeal events must have empty tags[]Yes

Client Behavior ​

Clients should:

  1. When creating a Seal:

    • Start with an unsigned event (rumor)
    • Encrypt it using NIP-44 with a key derived from the sender's private key and recipient's public key
    • Place the encrypted content in a kind 13 event with empty tags
    • Sign the Seal with the author's key

  2. When receiving a Seal:

    • Attempt to decrypt it using NIP-44 and the conversation key
    • Validate the decrypted content as a valid event structure
    • Note that the decrypted event is unsigned and should not be broadcast as-is

Seals are typically wrapped inside Gift Wrap events (kind 1059) for secure transmission.

Relay Behavior ​

Relays should:

  1. Treat Seal events like any other event for storage and validation
  2. Not attempt to decrypt or interpret the content

Use Cases ​

  • Secure messaging with metadata protection
  • Collaborative signing protocols
  • Deniable messaging (the rumor is unsigned)
  • Private content sharing

Example ​

json
{
  "id": "28a87d7c074d94a58e9e89bb3e9e4e813e2189f285d797b1c56069d36f59eaa7",
  "pubkey": "611df01bfcf85c26ae65453b772d8f1dfd25c264621c0277e1fc1518686faef9",
  "created_at": 1703015180,
  "kind": 13,
  "tags": [],
  "content": "AqBCdwoS7/tPK+QGkPCadJTn8FxGkd24iApo3BR9/M0uw6n4RFAFSPAKKMgkzVMoRyR3ZS/aqATDFvoZJOkE9cPG/TAzmyZvr/WUIS8kLmuI1dCA+itFF6+ULZqbkWS0YcVU0j6UDvMBvVlGTzHz+UHzWYJLUq2LnlynJtFap5k8560+tBGtxi9Gx2NIycKgbOUv0gEqhfVzAwvg1IhTltfSwOeZXvDvd40rozONRxwq8hjKy+4DbfrO0iRtlT7G/eVEO9aJJnqagomFSkqCscttf/o6VeT2+A9JhcSxLmjcKFG3FEK3Try/WkarJa1jM3lMRQqVOZrzHAaLFW/5sXano6DqqC5ERD6CcVVsrny0tYN4iHHB8BHJ9zvjff0NjLGG/v5Wsy31+BwZA8cUlfAZ0f5EYRo9/vKSd8TV0wRb9DQ=",
  "sig": "02fc3facf6621196c32912b1ef53bac8f8bfe9db51c0e7102c073103586b0d29c3f39bdaa1e62856c20e90b6c7cc5dc34ca8bb6a528872cf6e65e6284519ad73"
}

Gift Wrap Protocol ​

The Seal is part of the three-layer Gift Wrap protocol:

  1. Rumor - An unsigned event containing the actual content
  2. Seal (kind 13) - Wraps and encrypts the rumor, signed by the true author
  3. Gift Wrap (kind 1059) - Wraps and encrypts the seal, signed with a throwaway key

This layered approach provides:

  • Author privacy (the Gift Wrap uses a throwaway key)
  • Content privacy (the Seal encrypts the content)
  • Deniability (the Rumor is unsigned)

Decryption Process ​

To decrypt a Seal:

  1. Use NIP-44 with a conversation key derived from the recipient's private key and the sender's public key
  2. Parse the decrypted content as JSON to get the original rumor

References ​

Notes ​

  • The created_at timestamp in a Seal should be deliberately randomized to prevent time-based correlation attacks
  • Tags must always be empty in a Seal event
  • The inner rumor must always be unsigned
  • This event kind must typically be wrapped in a Gift Wrap event for proper security