Simple, secure cloud storage.

Simple Secure Storage Service (S4)

S4 is Least Authority's verifiably secure off-site backup system for individuals and businesses.

With S4, we can never see your data; you can always see our code. Learn more »

Just $25/month for unlimited storage (for personal use).


Robustly architected

Even if some servers go down, your data is still safe and available.

Built-in versioning

Easy access to previous revisions of your data.

Scales seamlessly

Built on top of Amazon S3; the future RAIC add-on will support Microsoft Azure, Rackspace, Google, and Hewlett-Packard as well.

Access control

Users can be given read-only or read-write access to individual files. Files can also be made immutable.

Easy to use

If you are familiar with the command line and can write a cron job, you can use S4 for backups.

Built-in API

Application developers can use S4 for storage as well via its API!

What makes us different?

100% client-side encryption

Unlike all the widely-used, PRISM-compatible services out there, S4 does client-side encryption on every file. The server that stores your data can't spy on your files even if it tries!

Open source transparency

Unlike other client-side-encryption services, S4 is free, open source software. Anyone can read the code and confirm that it doesn't have secret backdoors; you don't have to just take our word for it.

Unlike almost all other storage providers, S4 offers verifiable end-to-end security. Learn more about how S4 works »

User reviews

LAFS's design acknowledges the importance of verifiable end-to-end security through cryptography, Free/Libre release of software and transparent peer-reviewed system design.
— Jacob Applebaum, Tor Project developer and WikiLeaks volunteer
I was positively amazed about how easy it is to install and how well it works.
— Johannes Nix
Wider deployment of this type of file storage system [LAFS] would have an immediate impact on the quality of modern data protection.
— Comprehensive National Cybersecurity Initiative (CNCI), Report on National Cyber Leap Year Summit 2009
If you use only free/libre software, you control your local computing — but using the Internet raises other issues of freedom and privacy, which many network services don't respect. The Simple Secure Storage Service is an example of a network service that does respect your freedom and privacy.
— Dr. Richard Stallman, president of the Free Software Foundation
When it comes to support for open source, you guys are amazing. Many open source projects could aspire to be that good.
— Tony Arcieri
It's very well designed, a pleasure to see such a system.
— Geoffroy Couprie
You develop an application the way it is meant to be developed.
— Patrick McDonald
LAFS is an amazing piece of work!
— Pål Ruud

Forthcoming products

Simple Secure Storage Service (S4)

S4 is Least Authority's secure off-site backup system for individuals and businesses.

Available now!

Just $25/month for unlimited storage (for personal use).


Redundant Array of Independent Clouds (RAIC) will be a multi-cloud add-on to our other products.

Magic Folder

Magic Folder will be a "Dropbox-esque", friendly file-syncing utility.