VSS, which stands for Versioned Storage Service, is an open-source project designed to offer a server-side cloud storage solution specifically tailored for non-custodial Lightning supporting mobile wallets. Its primary objective is to simplify the development process for Lightning wallets by providing a secure means to store and manage the essential state required for Lightning Network (LN) operations.
In a non-custodial Lightning wallet, it is crucial to securely store and manage various types of state data. This includes maintaining a list of open channels with other nodes in the network and updating the channel state for every payment made or received. Relying solely on user devices to store this information is not reliable, as data loss could lead to the loss of funds or even the entire wallet.
To address this challenge, the VSS project introduces a framework and a readily available service that can be hosted by anyone as a Versioned Storage Service. It offers two core functionalities:
- Recovery: In the event of a user losing their phone or access to their app's data, VSS allows for the restoration of the wallet state. This ensures that users can regain access to their funds, even in cases of device or data loss.
- Multi-device Access: VSS enables multiple devices with the same wallet app to securely access and share LN state. This seamless switching between devices ensures consistent access to funds for users.
Clients can also use VSS for general metadata storage as well such as payment history, user metadata etc.
By providing a reusable component, VSS aims to lower the barriers for building high-quality LN wallets. Wallet developers have the flexibility to either host the VSS service in-house, enabling easy interaction with the component, or utilize reliable third-party VSS providers if available.
VSS is designed to work with various applications that implement different levels of key-level versioning and data-integrity mechanisms. It even allows for the disabling of versioning altogether for single-device wallet usage, making it simple to get started.
The project's design decisions prioritize features such as multi-device access, user privacy through client-side encryption(e.g. using key derived from bitcoin wallet), authorization mechanisms, data and version number verifiability, and modularity for seamless integration with different backend technologies.
VSS can work out-of-box with minor configuration but is intended to be forked and customized based on the specific needs of wallet developers. This customization may include implementing custom authorization, encryption, or backend database integration with different cloud providers. As long as the API contract is implemented correctly, wallets can effortlessly switch between different instances of VSS.
VSS ships with a PostgreSQL implementation by default and can be hosted in your favorite infrastructure/cloud provider ( AWS/GCP) and its backend storage can be switched with some other implementation for KeyValueStore if needed.
VSS execution is split into two phases: Phase I prioritizes recovery and single-device use, whereas Phase II covers multi-device use. Phase I is ready to use and integrated within LDK-node. Phase II will be subject to monitoring for demand from wallets and may slip to a later date. Refer to LDK-Roadmap for more details.
See the VSS API contract for details.
Currently, VSS-server has a Java-based implementation and is ready to use. Support for a Rust-based VSS-server is a work in progress. VSS-rust-client is a Rust-based client with support for client-side encryption, key obfuscation, retry mechanisms, and LNURL-auth. VSS is also integrated with LDK-node v0.4.x as alpha support.
- Build & Deploy: Refer to language specific folder for instructions related to build and deploy of VSS.
- Hosting: VSS can either be self-hosted or deployed in the cloud. If a service provider is hosting VSS for multiple users, it must be configured with HTTPS, Authentication/Authorization, and rate-limiting.
- Authentication and Authorization: Currently, the VSS-server supports JWT-based authentication and authorization, and can run without authentication for local testing or in trusted setups. The VSS-rust-client supports LNURL-auth & JWT based authentication and authorization. Switching to simple HTTP header authentication is straightforward by adding another implementation. Note that the security of authentication heavily relies on using HTTPS for all requests.
- Scaling: VSS itself is stateless and can be horizontally scaled easily. VSS can be configured to point to a PostgreSQL cluster, and further scaling considerations need to be addressed in the PostgreSQL cluster.
- Using with LDK-node: LDK-node can be easily configured to run with VSS as primary storage. It is integrated in
LDK-node (written in Rust) using VSS-rust-client, and there is also support for other languages such as Swift,
Kotlin and Python through UniFFI bindings.
use ldk_node::Builder; fn main() { let mut node_builder = Builder::new(); ... let node = node_builder.build_with_vss_store_and_fixed_headers(vss_endpoint, store_id, HashMap::new()).unwrap(); node.start().unwrap(); ... ... }
- Using with Other Applications: VSS is designed to store application-related metadata. Clients can use the VSS-rust-client directly for this purpose. This can help provide a complete user data recovery solution for applications, as well as enable turn-key multi-device support in the future.
In summary, VSS is an open-source project that offers a server-side cloud storage solution for non-custodial Lightning wallets. It provides multi-device access, recovery capabilities, and various features to ensure user privacy and data verifiability. By leveraging VSS, wallet developers can focus on building innovative Lightning wallets without the burden of implementing complex storage solutions from scratch.
If you encounter any issues or have questions, feel free to open an issue on
the GitHub repository. For further assistance or to discuss the
development of VSS, you can reach out to us in the LDK Discord in the #vss channel.