How to Handle Endpoint Identity with SecretKey in iroh

In iroh, an endpoint's identity is derived from a cryptographic SecretKey, which you can supply via the builder to create a stable, persistent identity across restarts.

The iroh networking library (n0-computer/iroh) uses cryptographic keys to establish peer identity. Each endpoint is identified by a SecretKey, and the public portion of this key becomes the EndpointId that other peers use to address you. Understanding how to manage this key is essential for building persistent, recognizable nodes in a distributed system.

Understanding Endpoint Identity Architecture

SecretKey Storage and Resolution

The Endpoint builder maintains an optional secret_key: Option<SecretKey> field that stores your identity configuration before binding. According to the source code in iroh/src/endpoint.rs, this field is defined at line 525. When you call Builder::bind(), the library resolves this key at lines 226–227, generating a fresh random key if you have not supplied one.

The secret key is ultimately stored inside the TLS configuration structure. In iroh/src/tls.rs at lines 46–48, the tls_config struct holds the secret_key that will be used for all cryptographic handshakes.

Identity Generation Flow

If you do not provide a custom key, iroh generates a random 32-byte key automatically. This occurs during the bind process in iroh/src/endpoint.rs (lines 224–236). While convenient for temporary connections, auto-generated keys result in a new EndpointId on every restart, requiring peers to rediscover your address.

Supplying a Custom Secret Key

The Builder Method

To maintain a consistent identity, call the secret_key method on the builder before invoking bind. The method signature in iroh/src/endpoint.rs (lines 524–527) is:

pub fn secret_key(mut self, secret_key: SecretKey) -> Self

This method consumes the builder and returns it with the identity configured, allowing chain construction.

Practical Implementation

Supply your own key to ensure peers can reconnect to you after a restart:

use iroh::{Endpoint, endpoint::presets};
use iroh_base::SecretKey;

// Load or create a secret key (e.g. from a file, env var, etc.)
let my_key = SecretKey::from_bytes(&[0x01; 32]); // replace with real key material

let endpoint = Endpoint::builder(presets::N0)
    .secret_key(my_key)           // set the identity
    .bind()
    .await?;

When you provide a custom key, the resulting EndpointId remains stable across application restarts, enabling long-term peer relationships.

Retrieving Identity Information

Accessing the SecretKey

After binding, you can retrieve the secret key reference using the accessor defined at lines 1172–1174 in iroh/src/endpoint.rs:

pub fn secret_key(&self) -> &SecretKey

This returns a reference to the stored key, which is useful for serialization or verification purposes.

Getting the Public EndpointId

To obtain the public identifier that peers use to reach your endpoint, use the id method. According to lines 1180–1182 in iroh/src/endpoint.rs, the signature is:

pub fn id(&self) -> EndpointId

This method derives the public key from the secret material and returns the EndpointId suitable for sharing with other nodes.

Security Best Practices

Key Confidentiality

The secret key must remain secret at all times. Possession of this key allows complete impersonation of your endpoint. Store it in secure hardware or encrypted storage, and never transmit it over unsecured channels.

Debugging with Key Logging

For development and debugging, iroh supports TLS key logging via Builder::keylog(true). This feature is implemented in iroh/src/endpoint.rs at lines 324–332. Never enable this in production, as it writes sensitive key material to disk, compromising the security of all connections.

Entropy Requirements

When generating custom keys, ensure the source provides at least 32 bytes of cryptographically secure random data. Weak or predictable keys expose your endpoint to brute-force attacks and identity theft.

Summary

• Supply a SecretKey via Builder::secret_key() before calling bind() to create a persistent endpoint identity.
• Retrieve the key using Endpoint::secret_key() or get the public identifier with Endpoint::id().
• Store keys securely and never enable keylog(true) in production environments.
• Auto-generated keys provide ephemeral identities suitable for temporary connections but require peer rediscovery after restarts.

Frequently Asked Questions

What is the difference between SecretKey and EndpointId in iroh?

The SecretKey is the private cryptographic material that proves your identity, while the EndpointId is the public derivative used by other peers to address you. The EndpointId is safe to share, but the SecretKey must be kept confidential to prevent impersonation.

How do I persist an endpoint identity across application restarts?

Serialize your SecretKey to secure storage (such as a file with restricted permissions or a hardware security module) after first generation. On subsequent starts, deserialize the key and pass it to Endpoint::builder().secret_key(your_key) before binding. This ensures your EndpointId remains constant.

Is it safe to enable key logging in production?

No. The keylog(true) method, found at lines 324–332 in iroh/src/endpoint.rs, writes TLS secrets to disk for debugging purposes. Enabling this in production exposes all cryptographic material and compromises connection security. Use it only during development.

What happens if I don't provide a SecretKey when building an endpoint?

If no key is supplied, Builder::bind() automatically generates a random SecretKey at lines 226–227 in iroh/src/endpoint.rs. This results in a new random EndpointId for every session, which is suitable for ephemeral connections but prevents peers from maintaining long-term address caches for your node.

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