Greenlight by Blockstream: Lightning Made Easy

Today we’re excited to unveil Greenlight, our latest Lightning Network service. The new service provides simple, secure access to the Lightning Network, allowing anyone to spin up their Lightning node in the cloud while retaining complete control over their funds.

Getting started with Bitcoin can be challenging, particularly when learning how to keep funds safe and private. Onboarding Lightning adds another layer of complexity because of the need to operate channels and liquidity as well as manage backups and watchtowers. New users often opt for custodial services where these technical challenges are managed for them but at the cost of trusting the service operator with their funds.

There is, however, a middle ground that we think is far better: use an operator to run the node with all of the associated challenges while keeping control over the funds with the user. This is precisely what Greenlight enables. Based on the highly modular and extensible open-source c-lightning implementation, we can run the node on our infrastructure while the user retains the keys on their own user device. Anything that touches your private keys requires signing by your device.

Lightning Simplified

Greenlight allows anyone to boot up their personal Lightning node on our cloud infrastructure in seconds and take full control over their funds. The private keys, required to sign both on-chain and off-chain transactions, never leave the user’s device.

Users interact with the node via a simple programmable interface and we take care of the rest. We schedule the node on our infrastructure when needed, managing everything from the Bitcoin back-end to encrypted backups and watchtowers. You take care of your funds, we’ll manage the rest.

When scheduled to run on the infrastructure, the node will attempt to connect to the user’s device which holds the keys and ask for sign-off on any operation that involves the user’s funds. When the user isn’t using their node, it shuts down automatically until it’s needed again. Starting the node is almost instantaneous, ensuring that the user experience is seamless.

The key differences from other setups can be summed up by the following:

• Security: Greenlight is non-custodial. While the nodes run on our infrastructure, our operations team never has access to your funds since keys are managed on the user’s device. Operations proposed by the node are verified on the user device before signing off on them.
• Low cost: c-lightning’s low resource footprint and the fact that nodes run on-demand means running a node using Greenlight is very inexpensive compared to other providers. During the initial testing phases of the service, users won’t be charged at all.
• One user, one node: Unlike bundling the node with the front-end app, Greenlight allows sharing a single node among any number of front-ends. This saves a lot of on-chain fees for the user, and reduces fragmentation of user funds. No more moving funds from your home node to your phone because you ran out of capacity.
• Simple recovery: Losing your phone at sea won’t mean losing your bitcoin. Since we manage the database and the backups, recovering the funds is as simple as initiating a new front-end with your seed phrase.
• On-board to off-board: Our main goal is to provide new users with a great first experience and a suitable starting point into the Bitcoin space. Conversely, we want users to eventually become knowledgeable enough to begin taking more control over their infrastructure. For that reason, we will offer users the option of exporting their node and loading it onto a platform of their choice.

A Tool for App Developers

As we mentioned above, one aspect of Greenlight is its user-friendliness that caters to newbies in the space, supporting them as they start their Bitcoin journey. Another important aim of ours is to empower developers building Lightning-enabled apps to innovate without needing to become node operation experts in the process. To help actualize this goal we’ve been working with two very exciting companies—Sphinx and Lastbit.

Sphinx Chat is a browser for the Lightning Network, where you can send and receive sats, form encrypted chat groups, and stream podcasts. By downloading the sphinx-relay onto Raspberry Pi hardware and connecting it to the Greenlight server, users can spin up a node and begin chatting in a matter of seconds without the overhead of syncing with the blockchain, installing a Lightning node, or setting up the rest of the infrastructure.

Lastbit is a technology platform that provides low-cost, instant payments around the world through the Lightning Network. Lastbit utilizes Greenlight through its simple web interface, Striga, which allows visitors to the website to spin up their personal node on demand without having to run any of the infrastructure themselves.

Availability

We want to ensure that users have the best possible experience when using Greenlight. In order to guarantee this, we plan to incrementally grant access to new users as we scale up in a controlled manner. At the moment, we onboard new users through our launch partners, which helps us improve the service before opening up to everybody. If you’d like to participate in the early phase and test the service firsthand, let us know.

This is but the first step in our journey. Currently, the service provides c-lightning nodes on demand. Looking ahead, you can expect additional features, such as automatic proposing channels, rebalancing liquidity, swap services, and much, much more.

Greenlight is available through Sphinx and Lastbit (currently on testnet), with an incremental rollout planned for the greater public after the initial beta phase. We encourage interested users to try out Greenlight via Sphinx or Lastbit.

The Road Ahead

This is just the beginning, and we are committed to improving and extending Greenlight with new features, security and privacy improvements, as well as improvements to the accessibility of the service as we learn together with our partners.

Blockstream holds a strong belief in setting realistic goals and not overpromising. Honoring this tradition, we’d like to share some of the open research questions and planned features, and how we plan to tackle them:

• Channel and liquidity management: This is likely the biggest stumbling stone for new users, whether Bitcoiner or new user. We’ll implement automation that proposes new channels to user nodes (both incoming and outgoing) to ensure the user node is always able to send and receive payments, without having to first learn these new concepts.
• Improving privacy: As operators of the infrastructure, we currently have access to metadata about the payments, which we’d like to reduce as much as possible. We plan to encrypt invoices and payments at rest, decryptable by the user devices. In addition, we plan to implement oblivious sends, a system in which the user device drives payments such that the node only sees encrypted routing onions, just like any routing node in the network.
• Strengthening security: Access control is currently relatively simple, and all client applications have the same level of access. More advanced scenarios may require delegating partial access to some applications, e.g., providing read-only access. In addition, we are researching ways to extend the verification to include this authorization layer, further minimizing the required trust in our infrastructure. This is an open area of research that could eventually enable hardware wallet support for Lightning. Rest assured, our findings will be open-sourced!

We are a small team, and some of these will undoubtedly take time. If these challenges sound interesting to you, and you’d like to help make them a reality, we are always looking for talented engineers to join our ranks. Just send us a message.