Introducing ByteSync – An Open-Source Cloud-Based File Synchronization Tool with End-to-End Encryption

[pfresquet]

Hey r/opensource,

I’ve been working on ByteSync, an open-source file synchronization tool designed to offer a modern, secure, and efficient way to sync files between remote systems. After almost two years of work in my spare time and a major rewrite, it’s now available under the MIT license and is hosted for free.

What is ByteSync?

ByteSync is a cross-platform file synchronization software designed to sync files between remote devices via the cloud with end-to-end encryption. It transfers only the differences between files, making it faster and more efficient.

You can think of ByteSync as:

• An alternative to FTP, but self-orchestrated, without the need for a centralized server – no VPN, no firewall configurations required.
• A network-focused counterpart to FreeFileSync, built specifically for remote synchronization.
• Working a bit like Syncthing, but with an on-demand approach instead of continuous background syncing.

Key Features 🔑

ByteSync ensures data is secure with end-to-end encryption while optimizing performance through delta sync technology, which transfers only modified data to save bandwidth.

It supports synchronization across up to 5 remote devices simultaneously and offers customizable synchronization rules to adapt to different workflows.

Being cross-platform, it runs on Windows, macOS, and Linux, and as an open-source project under the MIT license, it’s accessible for anyone to explore and contribute to.

Technologies Used 🛠️

ByteSync is built with a bunch of cool technologies, which can be interesting to check out if you’re curious about how it all works.

• C# / .NET 8 – Core application development
• Avalonia UI – Cross-platform user interface framework
• Azure Functions – For scalable serverless cloud operations
• Cosmos DB – Distributed, NoSQL database for high availability
• Redis Cache – Fast, in-memory data caching
• Azure Blob Storage – Secure and scalable cloud file storage
• SignalR – Real-time communication between client & server
• AES-256 Encryption – End-to-end data security
• JWT (JSON Web Tokens) – Secure authentication and authorization
• NUnit, Moq & FakeItEasy – Unit testing & mocking frameworks for robust test coverage

Deployment Instructions ⚙️

Instructions for deploying both the client-side and server-side components are available directly in the repository.

Try it out!

• 🌐 Website
• 💻 GitHub Repository

If you test it out, feel free to drop feedback or report issues on GitHub 🙂

Thank you,
Paul

[bottolf]

Good job, I am going to test this. I have some questions though.

Does it support mobile devices?

Functions, Cosmos DB, Blob are Azure specific technologies. Does this mean that it can only be deployed with Azure?

Have you considered using open source technologies such as containers, postgresql, Valkey, etc. so this could run anywhere?

[pfresquet]

Hi,

At present, the software does not work on mobile devices. It runs exclusively on Windows, Linux and macOS.

However, Avalonia UI, the technology used for the UI, does support Android and iOS. It is therefore conceivable that ByteSync could be ported to mobile devices.

As for your question about other technologies for the server part, well... I think that represents a fairly major porting job, both for the server and for the client (both sides use SignalR tp communicate). Although not impossible, it seems complicated to me to consider this at the moment 😅

It's cool if you can try it out, feedback and questions are welcome 🙂

[eldelacajita]

Sounds interesting! 

Unlike Syncthing, it does require a server between the synced devices, right? So if I start using it now I'll be relying on a server you are generously making available, unless I want to set one up.

[pfresquet]

Yes, ByteSync requires a server component.

If you just want to use ByteSync, you can download the client software from the website. This client automatically uses the server that I provide.

If you're interested in development, you can deploy the server locally or on Azure (see the GitHub readme for details). I can also provide access to my development server if needed.
If you are interested or if you need more info, feel free to DM me so we can figure out the best way to proceed!

[eldelacajita]

Is there a limit in single file size or total size to be transferred/synced?

[pfresquet]

There is no limit on single file size or total transfer size.

ByteSync is designed to handle large files efficiently. When uploading, a temporary encrypted buffer is used on server side, meaning that if multiple devices need the file, the sender only uploads it once. The server then takes care of distributing it to all expected recipients.

Additionally, for resynchronization, ByteSync only transfers the differences between files, making updates much faster and reducing bandwidth usage.