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Kind 7375: Cashu Token ​

Overview ​

A Cashu Token event (Kind 7375) stores encrypted ecash proofs that represent unspent funds in a Cashu wallet. These events track the state of a user's ecash tokens across different Nostr clients, allowing for interoperable wallet functionality. When tokens are spent, these events are deleted using NIP-09 and new events may be created with the remaining unspent proofs.

Specification ​

PropertyValue
Kind Number7375
Event RangeRegular
Defined inNIP-60

Content Format ​

The content field contains NIP-44 encrypted data with ecash token proofs from a specific mint.

Schema ​

json
{
  "content": "<nip44-encrypted-data>"
}

The encrypted data contains:

json
{
  "mint": "https://mint-url.example",
  "proofs": [
    {
      "id": "005c2502034d4f12",
      "amount": 1,
      "secret": "z+zyxAVLRqN9lEjxuNPSyRJzEstbl69Jc1vtimvtkPg=",
      "C": "0241d98a8197ef238a192d47edf191a9de78b657308937b4f7dd0aa53beae72c46"
    }
  ],
  "del": ["token-event-id-1", "token-event-id-2"]
}

Tags ​

This event typically doesn't have tags as the relevant information is encrypted in the content field.

Client Behavior ​

Clients should:

  1. Create Kind 7375 events when receiving ecash tokens
  2. Store multiple proofs in a single event, typically grouped by mint
  3. Encrypt the token data using NIP-44
  4. When spending tokens:
    • Delete the original event using NIP-09 (Kind 5)
    • Create a new event with the remaining unspent proofs, if any
    • Include a del field listing the token events that were destroyed in this process
  5. Include a tag ["k", "7375"] in the NIP-09 deletion event to allow easy filtering
  6. Validate proofs periodically to ensure they aren't already spent on the mint
  7. Create Kind 7376 events to maintain a spending history record

Relay Behavior ​

Relays should store and serve these events normally. However, they should also honor NIP-09 deletion requests to remove events when tokens are spent.

Use Cases ​

  • Storing ecash tokens securely within the Nostr protocol
  • Tracking unspent tokens across different Nostr clients
  • Managing the state of a user's Cashu wallet
  • Supporting cross-application ecash functionality

Example ​

json
{
  "id": "f9ef37824b4a15a265a7a35bc739dacfb535f36f68a623225ad9e8d98bc042dd",
  "pubkey": "79dff8f82963424e0bb02708a22e44b4980893e3a4be0fa3cb60a43b946764e3",
  "created_at": 1684327102,
  "kind": 7375,
  "content": "g8XAw7MftJJmbVtK0TQkPVzE8yUDdLNnhDG6e9HXR5XRFGiDXLMp6GXjGwOsj3sFQqxDGfPCCRRLvPz0Uc3zKszBsJHPcoDqJ5SFLLpDDLCf8bv0MuTxpzkwm5BM+xIJtXbTKEmdZBk9lOkvnxwi1uwR3Q7W+LXDZlufbYe4qqRUU7YjVpwBhDmwIbXK9Dnu3N8y4OQ/Q1ScdVgG8FcvDC8Y8o3UTrVYj7nL3nh6WHEFtC1C0r/n2Y+9nYCZjGw2XTFLr8yCBPLblzE45O9fgX1Hv6iKcC+L7OYR6ZCU/qPdp7Oi28roCyTy0/dEWYEKkLjNWHbGvFkUqQ0JlQOLv9xIRSPrXDjyXmFjDONFQvH34rkDyVUt21Z3Xn40?iv=TRTvgCBwXhXdKHjuhO9pjA==",
  "tags": [],
  "sig": "6b1adce7e6a48095f11e8b88039f598356bf9da96d9ef94d3ee930964030e48066cc9a9ee1bebd9add3f27f1a101111cf8724cb324cc3c91a0cdd009df14f88b"
}

When decrypted, the content would reveal:

json
{
  "mint": "https://stablenut.umint.cash",
  "proofs": [
    {
      "id": "005c2502034d4f12",
      "amount": 1,
      "secret": "z+zyxAVLRqN9lEjxuNPSyRJzEstbl69Jc1vtimvtkPg=",
      "C": "0241d98a8197ef238a192d47edf191a9de78b657308937b4f7dd0aa53beae72c46"
    },
    {
      "id": "005c2502034d4f13",
      "amount": 10,
      "secret": "k8nUzW6s5FRUgsTpfP2vZ4n81aCGj4QWZPrjB2wN8eE=",
      "C": "02e5fea8ed5eb027d3751b46ac35742cf881473c3c8791d5e6391f9839704651f7"
    }
  ],
  "del": ["a1b3c4d5e6f7a8b9c0d1e2f3a4b5c6d7e8f9a0b1c2d3e4f5a6b7c8d9e0f1a2b3"]
}

Example of a deletion event (Kind 5) for a spent token:

json
{
  "id": "3e44a3251c4a1be3f7e13a7a35bc739dac8f735f36f98a632225ad9e8d98c0e1",
  "pubkey": "79dff8f82963424e0bb02708a22e44b4980893e3a4be0fa3cb60a43b946764e3",
  "created_at": 1684328920,
  "kind": 5,
  "content": "",
  "tags": [
    ["e", "f9ef37824b4a15a265a7a35bc739dacfb535f36f68a623225ad9e8d98bc042dd"],
    ["k", "7375"]
  ],
  "sig": "a1d4c87c3b0d26e64af0d40f4c85a29faf79d78349823b0e7ba8fc2abfe690516c9219bef11ad4e6d889ce1b7d659170803a7337e4a77a96676a719d97634af9"
}

References ​

Notes ​

  • Multiple Kind 7375 events can exist for the same mint
  • When tokens are spent, the original event is deleted and a new one may be created with remaining tokens
  • The del field helps track state transitions by referencing token events that were consumed
  • Clients should periodically validate proofs to ensure they are still valid and unspent