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SSH Key Attestation

This document describes how to link your Nostr npub to SSH public keys for git operations over SSH.

Overview

GitRepublic supports SSH key attestation, allowing you to use standard git commands over SSH instead of HTTP with NIP-98 authentication. This is done by signing a Nostr event that proves ownership of an SSH key.

Important: SSH key attestations are stored server-side only and are not published to Nostr relays. They are only used for authentication on the GitRepublic server.

Prerequisites

You must have unlimited access (ability to write to at least one default Nostr relay)
You must have a Nostr key pair (via NIP-07 browser extension)
You must have an SSH key pair

SSH Key Comment Field

The SSH public key comment field (the part after the key data) can contain:

NIP-05 identifiers (e.g., user@domain.com) - recommended for Nostr users
Email addresses (e.g., user@example.com)
Any other identifier

The comment field is optional and does not affect the key fingerprint or authentication. It's purely for identification purposes.

How It Works

Generate SSH Key (if you don't have one):

ssh-keygen -t ed25519 -C "your-nip05@example.com"
# Or use RSA: ssh-keygen -t rsa -b 4096 -C "your-nip05@example.com"
# Note: The comment field (-C) can contain your NIP-05 identifier or email address

Get Your SSH Public Key:

cat ~/.ssh/id_ed25519.pub
# Or: cat ~/.ssh/id_rsa.pub

Create Attestation Event:
- Sign a Nostr event (kind 30001) containing your SSH public key
- The event must be signed with your Nostr private key
- Submit the event to the server via API
Server Verification:
- Server verifies the event signature
- Server stores the attestation (SSH key fingerprint → npub mapping)
- Server allows git operations over SSH using that key

API Usage

Submit SSH Key Attestation

Endpoint: POST /api/user/ssh-keys

Headers:

X-User-Pubkey: Your Nostr public key (hex format)

Body:

{
  "event": {
    "kind": 30001,
    "pubkey": "your-nostr-pubkey-hex",
    "created_at": 1234567890,
    "tags": [],
    "content": "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAI... your-nip05@example.com",
    "id": "event-id-hex",
    "sig": "event-signature-hex"
  }
}

Example using curl (with NIP-07):

// In browser console with NIP-07 extension:
const sshPublicKey = "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAI...";

const event = {
  kind: 30001,
  pubkey: await window.nostr.getPublicKey(),
  created_at: Math.floor(Date.now() / 1000),
  tags: [],
  content: sshPublicKey
};

const signedEvent = await window.nostr.signEvent(event);

// Submit to server
const response = await fetch('/api/user/ssh-keys', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/json',
    'X-User-Pubkey': await window.nostr.getPublicKey()
  },
  body: JSON.stringify({ event: signedEvent })
});

Get Your Attestations

Endpoint: GET /api/user/ssh-keys

Headers:

X-User-Pubkey: Your Nostr public key (hex format)

Response:

{
  "attestations": [
    {
      "eventId": "event-id",
      "fingerprint": "SHA256:abc123...",
      "keyType": "ssh-ed25519",
      "createdAt": 1234567890,
      "revoked": false
    }
  ]
}

Verify SSH Key

Endpoint: POST /api/user/ssh-keys/verify

Body:

{
  "fingerprint": "SHA256:abc123..."
}

Response:

{
  "valid": true,
  "attestation": {
    "userPubkey": "npub-hex",
    "fingerprint": "SHA256:abc123...",
    "keyType": "ssh-ed25519",
    "createdAt": 1234567890
  }
}

Revoking Attestations

To revoke an SSH key attestation, submit a new event with a revoke tag:

const event = {
  kind: 30001,
  pubkey: await window.nostr.getPublicKey(),
  created_at: Math.floor(Date.now() / 1000),
  tags: [['revoke', 'true']],
  content: sshPublicKey  // Same public key to revoke
};

const signedEvent = await window.nostr.signEvent(event);
// Submit to POST /api/user/ssh-keys

SSH Server Integration

Note: The current GitRepublic implementation provides the API for storing and verifying SSH key attestations. To use SSH for git operations, you would need to:

Set up an SSH server (e.g., using node-ssh-server or a traditional OpenSSH server)
Configure git-shell or a custom command handler
Verify SSH keys by:
- Extracting the SSH key fingerprint from the SSH connection
- Calling the verification API or using the verifyAttestation() function directly
- Allowing git operations if the key is attested

Example SSH Server Integration (Pseudocode)

import { verifyAttestation } from '$lib/services/ssh/ssh-key-attestation.js';

// In SSH server authentication handler
async function authenticateSSH(sshKey: string, fingerprint: string) {
  const attestation = verifyAttestation(fingerprint);
  
  if (!attestation) {
    return false; // Authentication failed
  }
  
  // User is authenticated as attestation.userPubkey
  // Allow git operations
  return true;
}

Git Configuration

Once SSH is set up, users can configure git to use SSH:

# Add remote using SSH
git remote add origin ssh://git@your-gitrepublic-server.com/repos/{npub}/{repo}.git

# Or use SSH URL format
git remote add origin git@your-gitrepublic-server.com:repos/{npub}/{repo}.git

Security Considerations

Attestations are server-side only: They are not published to Nostr relays, reducing privacy concerns
Rate limiting: Maximum 10 attestations per hour per user
Signature verification: All attestations must be signed with the user's Nostr private key
Revocation support: Users can revoke attestations at any time
Fingerprint-based lookup: SSH key fingerprints are hashed before storage (HMAC)

Environment Variables

SSH_ATTESTATION_LOOKUP_SECRET: Secret key for HMAC-based fingerprint lookup (default: 'change-me-in-production')
- Important: Set this to a secure random value in production!

Limitations

SSH server integration is not yet implemented in the main codebase
Attestations are stored in-memory (will be lost on server restart)
- In production, use Redis or a database for persistent storage
Only users with "unlimited access" can create attestations

Future Improvements

Persistent storage (Redis/database) for attestations
SSH server implementation
Support for multiple SSH keys per user
Key expiration/rotation policies
Audit logging for SSH operations

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