Proof Of Concept

In a world where decentralization often hinges on the strength of its weakest node, the idea of federation—applied not to content moderation or identity, but strictly to **communication protocols**—opens up intriguing possibilities. In this model, **Nostr relays** do not operate in total isolation, nor do they function in a single cohesive mesh. Instead, they **form selective, encrypted alliances**, communicating through **secure tunnels** while preserving autonomy.

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### 💡 The Core Idea

**Relays remain sovereign**, but may establish **peer-to-peer encrypted channels** with other trusted relays using **Elliptic Curve Diffie-Hellman (ECDH)** to generate shared secrets. These secrets are then used to encrypt communication tunnels—facilitating a federated communication layer.

Each relay is free to choose:

- **Whom it speaks to**

- **How often**

- **What types of events are relayed through the tunnel**

But *never* must it rely on a central coordinator.

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### 🔁 Schnorr for Authentication

While ECDH can create the secure tunnel, **Schnorr signatures** (already a part of Nostr’s pubkey-based design) can be used to **authenticate the origin** of the data inside. This keeps the integrity of messages intact even when traveling over shared or hostile networks.

Use case:

- Relay A and Relay B establish an ECDH-based shared key.

- All communication is tunnel-encrypted with this shared key.

- Inside the tunnel, every message still carries a Schnorr signature, proving its source.

This separation of **transport-level encryption** from **message-level authenticity** provides an elegant layering of security.

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### 🌐 Practical Benefits

- **Obfuscation**: Encrypted tunnels reduce visibility into relay-to-relay traffic patterns.

- **Privacy**: Federation over encrypted channels shields metadata and protects against surveillance.

- **Resilience**: Relays can route around censorship by tunneling through less obvious peers.

- **Synergy**: Specific relay clusters can form ephemeral or long-term alliances—say, art relays or academic relays—without disclosing their full graph to the world.

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### 🧩 Optional Enhancements

- **Noise Protocol Framework** to standardize encrypted relay tunnels.

- **Tor Hidden Services** or **I2P** for transport obfuscation.

- **Relay Reputation Systems** to gauge trust before federation.

- **Dynamic Federation Negotiation**: using NIP-like proposals over encrypted handshakes to initiate or terminate communication agreements.

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### 🌱 Case In Point

This is not about governing content, users, or identities—this is about strengthening how relays *talk*. By embracing federated communication via ECDH and Schnorr-secured tunnels, Nostr relays could evolve into a resilient underground of trust-minimized, pseudonymous routers that defy surveillance while amplifying decentralization.

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**federated communication via ECDH and Schnorr-authenticated encrypted tunnels between Nostr relays**:

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```markdown

NIP-xyz: Federated Encrypted Relay Communication

Status: Draft

Type: Relay

Created: 2025-04-22

```

---

## Summary

This NIP proposes a method for **encrypted, authenticated communication between Nostr relays** using **ECDH-based tunnels** for transport encryption and **Schnorr signatures** for payload integrity. This federation model allows relays to communicate securely while maintaining full autonomy, enhancing privacy, censorship resistance, and interoperability.

---

## Motivation

Nostr’s decentralized architecture relies heavily on relays, which currently operate in isolated or broadcast modes. There is no standard for secure, peer-to-peer communication **between relays themselves**, outside of client interactions.

Introducing encrypted tunnels between relays offers:

- **Privacy**: Reduces metadata leakage across public or adversarial networks.

- **Resilience**: Allows relays to forward events and metadata through trusted peers when direct access is blocked or filtered.

- **Autonomy**: Federation is opt-in and purely communicational—no centralized authority or directory is involved.

- **Extensibility**: Enables experimental protocols or content-specific subnets without altering the global Nostr model.

---

## Specification

### 1. Key Exchange via ECDH

Each relay maintains:

- A persistent **relay keypair**: `relay_pubkey`, `relay_privkey`

- Optionally: rotating session keys for forward secrecy

When two relays (A and B) wish to establish communication:

- They exchange their public keys (`relay_pubkey_A` and `relay_pubkey_B`)

- Both calculate a shared secret using ECDH over `secp256k1`:

```plaintext

shared_secret = SHA256(ECDH(relay_privkey_A, relay_pubkey_B))

```

This `shared_secret` is used to derive an encryption key for an **authenticated symmetric cipher**, such as AES-GCM or ChaCha20-Poly1305.

---

### 2. Encrypted Tunnel Establishment

Once the shared secret is derived:

- All messages between relays are sent through an **encrypted tunnel**

- Transport can be TCP, WebSocket, or HTTP/3 over QUIC, optionally via Tor or I2P

A **RelayHello** message is exchanged encrypted, optionally containing:

```json

{

"type": "relay_hello",

"relay_name": "nostr.relay.example",

"features": ["forwarding", "dedup", "metadata"],

"timestamp": 1684000000,

"sig": ""

}

```

The `sig` is a Schnorr signature from the `relay_pubkey`, verifying the message content.

---

### 3. Event Forwarding

Relays may forward selected event types across tunnels, such as:

- Kind 1 (Text Note)

- Kind 3 (Contacts)

- Kind 5 (Deletion Notices)

- Custom kinds (with mutual agreement)

All forwarded events MUST retain original client-level signatures. Relay-to-relay metadata (like timestamps, relay hints, or scores) may be added in a separate metadata envelope.

---

### 4. Access Control and Policies

Each relay maintains a **federation list**, including:

- Public key of the peer relay

- Features enabled

- Rate limits and quotas

- Last active session or rotation timestamp

Relays MAY:

- Deny tunnel requests

- Rotate keys periodically

- Restrict communication to a whitelist

- Use Proof-of-Work or tokens for DoS protection

---

### 5. Optional Features

- **Forward Secrecy**: ephemeral key pairs with HKDF for short sessions

- **Relay Reputation**: signed relay trust scores (future NIP)

- **Message Compression**: gzip or zstd on tunnel payloads

- **Encrypted Gossip**: tunnel-specific metadata routing

---

## Compatibility

This NIP is **backward-compatible**. Relays that do not implement it will simply not participate in tunnel-based communication.

No changes are required from Nostr clients.

---

## Reference Implementation (Proposed)

- `nostr-tunnel-relay`: Rust-based relay that supports federated encrypted tunnels

- `nostr-relay-link`: CLI tool to establish and monitor tunnels

- Example configs for federation policies in JSON or TOML

---

## Rationale

- ECDH ensures only the two relays involved can decrypt tunnel data

- Schnorr signatures authenticate content without duplicating identity schemes

- Federation is scoped **only to communication**, preserving Nostr’s core simplicity

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## Security Considerations

- Relay pubkeys must be carefully verified to prevent MITM

- Session expiration and key rotation should be configurable

- Replay protection and nonce management are required for AEAD ciphers

- Metadata leakage minimized by default obfuscation or Tor-based transport

---

NIP.eshgham