Tresorit
Tresorit is an online cloud storage service based in Switzerland and Hungary that emphasizes enhanced security and data encryption for businesses and individuals. The Business version offers up to 1TB of storage space per user (the Solo version offers 2TB for one user) and extra security features such as DRM, granular access levels and other functions, which Tresorit cites to creating a safer collaborative environment. 
Tresorit's service is accessible through client desktop software, a web-based application and mobile apps. Currently, the software is available for Windows, macOS, Android, Windows Phone 8, iOS, and Linux.
Currently as of 2021, Swiss Post owns a majority stake in the cloud storage service. Tresorit works as an independent entity under Swiss Post.

History

Tresorit was founded in 2011 by Hungarian programmers Istvan Lam, who remains CEO, Szilveszter Szebeni, who is currently CIO and Gyorgy Szilagyi, who is the CPO of the company.

Tresorit officially launched its client-side encrypted cloud storage service after emerging from its stealth beta in April 2014.

In August 2015, Wuala (owned by LaCie and Seagate), a pioneer of secure cloud storage, announced it was closing its service after 7 years, and recommended their users to choose Tresorit as their secure cloud alternative.

By the end of 2016, Tresorit launched a beta of the software development kit (SDK) ZeroKit. In January 2017, Apple's SDK project CareKit announced the option for mobile app developers using CareKit to integrate ZeroKit, enabling zero knowledge user authentication and encryption for medical and health apps.

Technology
Tresorit claims to encrypt files using client-side encryption with AES-256 before uploading them. Files are also secured by HMAC message authentication codes applied on SHA-512 hashes.

"Tresors" (German for safes) are encrypted counterparts of uploaded directories. Tresors automatically sync with the cloud as files are added or removed from them, similar to Box.com and Dropbox's desktop software. The main difference between Tresorit and its competition is that Tresorit applies AES-256 client-side encryption to files while they are still local and then uploads them to the cloud. The company claims that due to its end-to-end encryption, users can share protected files and folders with others and work together on them, keeping the documents synced and secure in every step of the process. There are additional layers of security, but the core privacy feature of the service is that the encryption key never leaves the user: Using Zero-Knowledge encryption protocols, Tresorit is not in possession of the users’ authentication data, so the content of files cannot be accessed from their servers nor delivered to authorities upon request.

Hacking contest
In 2013 and 2014, Tresorit hosted a hacking contest offering $10,000 to anyone who hacked their data encryption methods to gain access to their servers. After some months, the reward was increased to $25,000 and later to $50,000, challenging experts from institutions like Harvard, Stanford or MIT. The contest ran for 468 days and according to the company, nobody was able to break the encryption.

Reception
Tresorit has received a number of nominations and awards. Up-Cloud Rewards named it one of the top 5 Cloud security solutions for 2012. Early 2016, Forbes listed Tresorit's cofounder Istvan Lam among the European "30 under 30". In 2017, Tresorit was listed as finalist in the Cybersecurity Excellence Awards, category Encryption.

See also
 Comparison of file hosting services
 Comparison of online backup services
 Encryption
 Remote backup service

References

File sharing services
Cloud storage
Cloud applications
Online backup services
Data_synchronization
Email attachment replacements
File hosting
File hosting for macOS
File hosting for Windows
File hosting for Linux
MacOS software
Linux software
Cryptographic software
Office software
Companies' terms of service