nips/404.md

# NIP-404: Ephemeral Events

`draft` `optional`

This NIP introduces a protocol for creating ephemeral events that are weakly tied to a public key, allowing ephemeral interactions without permanent attachment to the author's identity.

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### TL;DR
This is a form of key delegation with "expiration" based on proof of work difficulty.

The main key generates a new key and uses the first chars of that new npub as a challenge. Anyone that solves that
challenge and finds an npub that matches it can publish as the main key. Because it is proof of work, it will become 
easier and easier to solve over time. Which creates some form of plausible deniability for the author.

Clients have to warn users that the new key might not represent the author anymore based on the time it has passed and the proof of work required by the author.

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## Rationale

Nostr is a great protocol, but the fact that each published event is eternally tied to a public key (`npub`) presents a dilemma for users:

- When you post something under your public key:
  - You are permanently linked to that event, leaving no room for privacy or a "right to be forgotten."
  - You cannot freely make mistakes or change your mind later, especially when you're young.
  - Posting impulsively—when drunk or not thinking clearly—becomes a permanent record.
  - You are essentially bound to your mistakes forever.
- If you regret posting something, you can claim that you were hacked. However, this undermines trust in your public key, effectively destroying your digital identity.
- Using a new public key for each event sacrifices the ability to maintain a long-term identity.

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## How Centralized Social Media Platforms Handle This

- **Temporary Stories**: Platforms like Instagram, Snapchat, and Facebook allow users to post stories that disappear after a set period.
- **Temporary Messages**: Messaging platforms like Signal, WhatsApp, and Telegram enable users to send messages that disappear after being read.

Because these platforms are centralized and closed-source, they can enforce "digital scarcity" on content, ensuring it disappears over time.

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## Objective

Nostr is decentralized, meaning that once an event is published, it becomes a permanent record on the internet.

As AI progresses, however, the content of an event alone becomes insufficient to prove authorship. Instead, people increasingly rely on cryptographic mechanisms to verify authorship.

This NIP introduces a protocol for creating temporary events that are weakly tied to a public key, enabling ephemeral interactions without permanently binding them to the author's identity.

We aim to produce events that are weakly tied to other public keys — events that are **probably** associated with that public key (e.g., Alice's) but cannot be **proven** to originate from it.

Additionally, we want to control the time window during which an event is likely from Alice. As time passes, the certainty of authorship decreases because more people had the opportunity to solve the challenge.


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## Implementation

The author (Alice) will create a new key pair and use an arbitrary number of initial characters from the new `npub` as 
a hint for the **challenge event** -- that is signed by Alice's main key.

The challenge involves mining an `NSec` that generates an `Npub` beginning with the hint provided in Alice's challenge event.

Whoever mines the `NSec` can publish an **ephemeral event** signed by the mined `NSec`. This event references the challenge event,
enabling verification of the solved challenge.

The **ephemeral event** public key is, therefore, completely detached from Alice's main key, making it impossible to 
prove that Alice was the solver.

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### Time Window

To establish a chronological anchor for the challenge, Alice can use her timestamp when creating the challenge event.
There is no really good reasons to lie about the timestamp.
1) If she picks a timestamp in the future, she will give more time to others to solve the challenge, so
people can impersonate her more easily.
2) If she picks a timestamp in the past, clients will see that the **challenge event** is old and will know that 
the **ephemeral events** that reference it are less likely to be from Alice.

Alice controls the time window of the challenge in two ways:
1. By selecting the **challenge event** timestamp.
2. By choosing the complexity of the challenge.
3. [Optional] She also can use put a 'ref' tag in the **challenge event** to reference a previous event, so we can
add a lower bound -- this is useful if you want to respond to a previous event.
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### Client Behavior

Clients can display a warning indicating that an event is ephemeral and uncertain. They can also show how much time has 
passed since the challenge was published. Clients may choose to stop displaying events that are too old or uncertain.

This feature can integrate with [NIP-44](40.md) to enhance the user experience.

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### Relays

*TODO*

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## Algorithm 

(need review, copilot autocompleted a bit 🤡 ) 
1. Alice generates a random key pair: (`Random NPub`, `Random NSec`).
2. Alice publishes a **challenge event** signed by her primary key, containing the following fields:
   - `pubkey`: `Random NPub`
   - `content`: The challenge.
   - `tags`: 
     - `["p", "<Alice's NPub>", "author"]`: Marks Alice as the author.
     - `["hint", "<first_n_digits_of_Random_NPub>"]`: Provides a hint for the solution.
     - `["ref", "<previous_event_id>"]`: References a previous event. (Optional)
     - `["challenge"]`: Indicates this is a challenge event.
3. Alice (or anyone) solves the challenge and publishes **ephemeral events** signed by the `Random NSec`, containing:
   - `pubkey`: The `Random NPub` if Alice solved it, or a mined `Npub` if someone else solved it.
   - `content`: The usual event content.
   - `tags`: 
     - `["p", "<Alice's NPub>", "author"]`: Tags Alice as the author.
     - `["challenge", "<challenge_event_id>"]`: Links to the challenge event.
     - `["ephemeral"]`: Indicates this is an ephemeral event.

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## Security Considerations

- The `hint` length can be adjusted to balance the ease of mining by powerful actors with the desired temporary nature of the event.
- Over time, the likelihood that others can solve the challenge increases, reducing confidence in Alice's authorship.
- Shortly after receiving the event, Bob can be reasonably confident it came from Alice. However, this confidence diminishes with time.