RLN Remote Signer

Overview

RGB Lightning Node (RLN) can run in external-signer mode. In this mode the node holds no seed and no private keys. Every signing operation it needs — channel signing, node cryptography (ECDH, inbound payments, peer storage, offers), and RGB PSBT signing — is answered by a signer built on Validating Lightning Signer (VLS). VLS does not sign blindly: it checks every request for protocol correctness and against its policy before producing a signature, and rejects anything that fails. External-signer mode is part of the Utexo RLN (#27, #95) and is used by the Utexo WDK today. Like the rest of RLN it is in beta: on mainnet, RLN supports on-chain RGB operations only.

Deployment modes

Mode	Where the seed lives	Use when
In-process signer (`NativeExternalSigner`)	In the host application’s secret storage (for example the WDK secret manager, Keystore, or Keychain). VLS runs inside the same process as the node.	Mobile and wallet integrations. This is the mode used by `@utexo/wdk-rgb-lightning`.
Remote signer daemon (`rln-signer-daemon`)	In a separate process, typically on a separate host. The node is watch-only and connects to the daemon over TCP.	Server deployments that isolate keys from the node host.

Both modes share one signer contract (rln-external-signer) and a VLS core patched for RGB channels.

Validation flow

[RGB Lightning Node] --> proposes a transaction or state update
        |
        v
[VLS signer] --> checks protocol correctness + policy
        |
        +-- valid   --> returns signature
        |
        +-- invalid --> rejects request

Because the keys never reach the node:

Reduced attack surface: a compromised node cannot read signing keys.
Policy enforcement: the signer refuses requests that break protocol rules or its policy.
Self-custody: keys stay in the environment you control.

What changes in external-signer mode

Operation	Behaviour
Asset issuance (NIA, CFA, IFA, UDA) and inflation	Not supported. Returns `UnsupportedInExternalSignerMode`.
`POST /burn` (BFA burn, from `v0.15.0-beta.3`)	Not supported. Returns `UnsupportedInExternalSignerMode`.
`POST /changepassword`, `POST /restore`	Not supported. Returns `UnsupportedInExternalSignerMode`.
`POST /backup`	Not available. File backups are encrypted with the node password, and an external-signer node has none. Use VSS cloud backup instead; it supports external-signer mode.
Authentication	Required. The node refuses to configure or unlock external-signer mode when started with `--disable-authentication` (`ExternalSignerRequiresAuthentication`). Use Biscuit tokens.
Restart	The same signer must be attached. A different signer identity is rejected with `ExternalSignerMismatch` before any channel state is read.
Secrets on the node	None. The node stores only public signer metadata (`key_source.json`).

Run the remote signer daemon

The daemon and the node’s remote-signer support are behind the remote-signer cargo feature. It is not enabled in the default build or the Docker image, so build from source:

cargo build --release --locked --features remote-signer
# produces target/release/rgb-lightning-node and target/release/rln-signer-daemon

Start the daemon

rln-signer-daemon \
  --seed-file /secure/signer/seed.hex \
  --network bitcoin \
  --listen-addr 127.0.0.1:9737

A new seed is generated (file mode 0600) if --seed-file does not exist. The daemon keeps its VLS state in --data-dir (default: a signer-db directory next to the seed file). Persist this directory — it is what lets a restarted daemon keep signing for existing channels.--network accepts bitcoin, testnet, signet, or regtest.

Print the signer identity

rln-signer-daemon --seed-file /secure/signer/seed.hex --network bitcoin --print-bootstrap

This prints the daemon’s bootstrap identity as JSON and exits.

Start the node pointing at the daemon

rgb-lightning-node dataldk0/ \
  --daemon-listening-port 3001 \
  --ldk-peer-listening-port 9735 \
  --network mainnet \
  --root-public-key <YOUR_PUBLIC_KEY> \
  --remote-signer-addr 127.0.0.1:9737

Initialise external-signer mode

Send the bootstrap JSON from step 2 to the locked node:

curl -X POST http://localhost:3001/initexternalsigner \
  -H "Authorization: Bearer <ADMIN_TOKEN>" \
  -H "Content-Type: application/json" \
  -d @bootstrap.json

The node probes the daemon at --remote-signer-addr and rejects the request if the submitted identity does not match the live daemon.

Unlock

Call POST /unlock as usual. In external-signer mode the password field is not checked; the Biscuit token is the credential that protects the node.

Securing the signer link

Side	Setting
Daemon	`--tls-cert` and `--tls-key` enable TLS. The certificate SAN must include `rln-remote-signer`. `--client-ca` enables mTLS and authenticates the node.
Daemon	A non-loopback `--listen-addr` is refused unless mTLS is configured. `--allow-unauthenticated-remote-signer` overrides this; use it only when the link is already secured by other means, such as a WireGuard tunnel.
Node	Place `ca.pem` in `<data-dir>/remote-signer-tls/` to verify the daemon certificate. Add `client.pem` and `client.key` to the same directory for mTLS.

If remote-signer-tls/ca.pem is missing, the node connects to the daemon without TLS. Always provision the TLS directory when the node and the signer are not on the same host.

--permissive relaxes the VLS policy for development and testing. Never use it with real funds; the daemon refuses it on mainnet.

What Utexo Is

Getting Started

Product Suite

API Reference

Overview

Deployment modes

Validation flow

What changes in external-signer mode

Run the remote signer daemon

Securing the signer link

​Overview

​Deployment modes

​Validation flow

​What changes in external-signer mode

​Run the remote signer daemon

​Securing the signer link

​Related

Overview

Deployment modes

Validation flow

What changes in external-signer mode

Run the remote signer daemon

Securing the signer link

Related