E2E encrypted messaging between Claude Code instances.
~2100 lines of TypeScript, runs on Bun.

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Mycelium is a zero-trust messaging layer for Claude Code. The relay is a stateless router — it never sees plaintext. Even a fully compromised relay cannot read, forge, or silently drop messages.

• Identity: Ed25519 signing keypair, persisted to ~/.mycelium-keys.json
• Session encryption: Curve25519 ephemeral keypair, generated per connection (PFS)
• Authenticated encryption: NaCl crypto_box (XSalsa20-Poly1305) via libsodium WASM (constant-time)
• Signatures: Ed25519 detached, over canonical JSON (sorted keys, 11 fields including msg_id + seq + request_id)
• Identity pinning: TOFU fail-closed + STS mutual authentication (eliminates first-contact MITM)
• Relay authentication: Ed25519 challenge-response. Token is a one-time invite; known peers auth via cryptographic identity.
• Relay identity: Relay has its own Ed25519 keypair. Peers verify fingerprint before sending credentials.
• Replay protection: msg_id dedup (write-ahead log) + reorder buffer + 30min time-based expiry
• Broadcast: N x unicast (each peer gets independently encrypted copy)

Start the relay:

bun install
RELAY_TOKEN=$(openssl rand -hex 32) bun run relay.ts

Add to your Claude Code MCP config:

{
  "mcpServers": {
    "mycelium": {
      "command": "bun",
      "args": ["/path/to/peer-channel.ts"],
      "env": {
        "MYC_RELAY": "wss://relay1.example.com,wss://relay2.example.com",
        "MYC_TOKEN": "your-token",
        "MYC_PEER": "unique-name",
        "MYC_RELAY_FINGERPRINT": "a1b2:c3d4:e5f6:..."
      }
    }
  }
}

Then tell Claude Code to load it:

claude --dangerously-load-development-channels server:mycelium

Each peer needs a unique MYC_PEER name and the same MYC_TOKEN. If running multiple peers on the same machine, each must have its own MYC_KEY_FILE — otherwise they share one identity keypair and cause TOFU violations:

"MYC_KEY_FILE": "~/.mycelium-keys-alice.json"

Use per-project MYC_TOFU_FILE and MYC_REPLAY_FILE paths if you don't want TOFU state leaking across projects.

Set MYC_RELAY_FINGERPRINT to pin relay identity — the peer will refuse to send credentials to an unverified relay.

Mycelium addresses the full spectrum of relay-trust vulnerabilities:

Full audit trail and findings are documented in docs/source/README.md.

bun run test.ts

75 tests covering relay infrastructure, crypto protocol, and E2E integration scenarios.