Today is a special day for Nextcloud and me because Nextcloud gets a cool and important new capability. This is end to end encryption for file sync and share. Nextcloud supports server side encryption for a long time and all file transfer over the internet is encrypted with

TLS/SSL of course. But there is still the need for full end to end encryption to make sure that the data is secure in all scenarios. One

example is that the current server side encryption doesn’t protect the data against an evil server admin or if the server is hacked. The new end to end solution does that.

This feature is more important then ever in the light of Trump and other governments including western ones like the UK who want to have access to the private data of users.

Please read this blog post about the upcoming dangers in the next few months. European datacenter is no solution, recent developments show

Most requested feature

End to end encryption is our most ever requested feature. Users and customers have been asking for this for many many years so I am super happy that we finally do this now. So you might ask “what took you so long?” There are many reasons.

The first is that it is hard. This needs to be done without compromising the user experience. Then we wanted to support as many core Nextcloud features as possible, for example sharing. And we wanted to do this in a way that doesn’t compromise performance. Obviously security is the highest priority and that is hard in itself. But another must have requirement is to make the feature truly enterprise ready. So real key management is necessary and it has to be designed with the assumption that users make mistakes. We don’t need another solution that is aimed at technical users, losing their data when they forget their password for example… Our solution doesn’t even let users pick their own password, taking away the risk of passwords that are easy to hack due to reuse or shortness! We also wanted to implement this feature fully transparent and native in all clients and fully open source instead of integrating a third party tool. It was hard to find a solution that balanced all these requirements. But I’m happy to say that Björn, who already designed and developed the server side architecture and Lukas our security lead, found a good architecture, with a lot of feedback from a number of other team members of course. This has been a real collaborative effort, building on our years of experience and a good understanding of the needs of our users and customers.

How does it work?

The feature consists of several components. There is the actual encryption and decryption code which is implemented in the Nextcloud iOS and Android apps and in the Mac, Windows and Linux clients. And then there is a server component which is implemented as a Nextcloud app to do the key management. This is useful to make it easy for the users to distribute private and public keys to all clients and share with each other. Obviously the private keys are encrypted with very strong auto generated passwords which are only known by the users and clients and are never accessible by the server. The key server also supports an optional recovery key which can be activated to make it possible to recover lost passwords/keys. This feature can be activated or deactivated to balance user convenience and security. The clients will warn users when the feature is or gets enabled.

End to end encryption can be activated by the users on a folder by folder basis. Once a user decided to encrypt a folder everything inside the folder will be encryption including the content of the files and folder and the metadata like filenames. From now on the folder is no longer accessible from the Nextcloud web-interface and WebDAV. But it is still fully readable and writable from iOS, Android and Mac, Windows, Linux. Sharing still works via public keys of other users. The full design is explained here and the architecture is further documented here

Enterprise ready

It was a key requirement to implement this feature in a way that it is not only useful for home users who want to protect their data on home-servers or at service providers. It had to be done in a way that it is useful for companies and other large organisation. We had conversations with some of our bigger customers over the last few month to make sure that this integrated nicely into the enterprise infrastructure and is compliant with existing policies. One example is that we will try to integrate this into Desktops like KDE, Gnome, Mac and Windows and will support Hardware Security Modules.

Where are we today?

This feature will be fully production ready and included in Nextcloud 13 which will be out later this year. But we didn’t want to wait until then and announce and release something as soon as possible so we can get feedback from encryption experts and the wider infosec community. So today we have our architecture document ready here. The server component is fully implemented and can be found in our github. There is a preview version of the Android app available which is fully working. The Desktop client and the iOS app are in the middle of the development. You can expect preview builds in the next few days. You can see the development and give feedback in the repositories in github.

More information can be found here:

The software can be found here:

So please give feedback about the architecture and the code if you want to get involved. This is a big step forward to protect the data of users and companies against hackers and organisations who want to abuse it in various ways!