Threema

Threema is a paid open-source end-to-end encrypted instant messaging application for iOS and Android.[6]

Threema
App Icon
Developer(s)Threema GmbH
Initial releaseDecember 2012 (2012-12)[1]
Stable release
iOS4.6.5 / February 1, 2021 (2021-02-01)[2]
Android4.5 / February 3, 2021 (2021-02-03)[3]
Written inObjective-C (iOS), Java (Android), C, .NET (Windows Phone)
Operating systemiOS, Android, Windows Phone
Available inEnglish, German, French, Spanish, Italian, Russian, Brazilian Portuguese, Polish, Rumantsch Grischun
TypeEncrypted instant messaging & voice calling
LicenseAGPLv3 (Apps, Web client)[4]
MIT (Communication protocol)[5]
Websitethreema.ch

The software is based on the privacy by design principles as it does not require a phone number or any other personally identifiable information. This helps anonymize the users to a degree.[7][8][9]

In addition to text messaging, users can make voice and video calls, send multimedia, locations, voice messages and files.[10] A web app version, Threema Web, can be used on desktop devices.[11]

Threema is developed by the Swiss company Threema GmbH.[12][13] The servers are located in Switzerland and the development is based in Pfäffikon SZ. As of January 2020, Threema had 8 million users.[14] As of January 2019, the business version, Threema Work, was used by 3,000 companies and organizations.[15]

History

Threema was founded in December 2012 by Manuel Kasper.[16] The company was initially called Kasper Systems GmbH.[17] Martin Blatter and Silvan Engeler were later recruited to develop an Android application that was released in early 2013.[18]

In Summer 2013, the Snowden leaks helped create an interest in Threema, boosting the user numbers to the hundreds of thousands.[19] When Facebook took over Whatsapp in February 2014, Threema got 200,000 new users, doubling its userbase in 24 hours.[20] Around 80% percent of those new users came from Germany. By March 2014 Threema had 1.2 million users.[18]

In Spring 2014, operations have been transferred to the newly created Threema GmbH.[17][21]

In December 2014, Apple listed Threema as the most-sold app of 2014 at the German App Store.[22]

In 2020, Threema expanded with video calls,[23] plans to make its codebase fully open-source as well as introduce reproducible builds[24] and Threema Education, a variation of Threema intended for education institutions.

During the second week of 2021, Threema saw a quadrupling of daily downloads spurred on by controversial privacy changes in the WhatsApp messaging service. A spokesperson for the company also confirmed that Threema had risen to the top of the charts for paid applications in Germany, Switzerland, and Austria.[25] This trend continued into the third week of the year, with the head of Marketing & Sales confirming that downloads had increased to ten times the regular amount, leading to "hundreds of thousands of new users each day".[26]

Features

Threema uses a user ID, created after the initial app launch by a random generator, instead of requiring a linked email address or phone number to send messages. It is possible to find other users by phone number or e-mail address if the user allows the app to synchronize their address book.[27] Linking a phone number or e-mail address to a Threema ID is optional. Hence, the service can be used anonymously. Users can verify the identity of their Threema contacts by scanning their QR code, when they meet physically. The QR code contains the public key of the user, which is cryptographically tied to the ID and will not change during the lifetime of the identity.[28] Using this feature, the users can make sure they have the correct public key from their chat partners, which provides additional security against a Man-in-the-middle attack. Threema knows three levels of verification (trust levels of the contact's identity). The verification level of each contact is displayed in the Threema application as dots next to the corresponding contact.

Users can make voice calls and send text messages, multimedia, locations, voice messages and files of any type (up to 50 MB per file).[10][29] It is also possible to create polls in personal or group chats.[30] With Threema Web, a client for web browsers, Threema can be used from other devices like desktop computers. Threema optionally supports Android Wear smartwatch and Android Auto.[31] Threema launched support for end-to-end encrypted video calls on August 10, 2020. The calls are person-to-person with group calls unavailable.[23]

Threema Work: On May 25, 2016, Threema Work, a corporate version of Threema, was released. Threema Work offers extended administration and deployment capabilities.[32] Threema Work is based on a yearly subscription model.[33]

Threema Gateway: On March 20, 2015, Threema released a gateway for companies. Similar to an SMS gateway, businesses can use it to send messages to their users who have Threema installed.[34] The code for the Threema Gateway SDK is open for developers and available on GitHub.[35]

Threema Broadcast: On August 9, 2018, Threema released Threema Broadcast, a tool for top-down communication. Similar to emails in electronic newsletters, Threema messages can be sent to any number of feed subscribers, and the Threema Broadcast allows to create chatbots.[36]

Threema Education: On September 10, 2020, Threema released Threema Education, a version of its messenger designed for education institutions. The app integrates Threema Broadcast and requires a one-time payment for each device used. It's intended for use by teachers, students, and parents.[37]

Privacy

Since Threema's servers are located in Switzerland, they are subject to the Swiss federal law on data protection. The data center is ISO/IEC 27001-certified.[38] Linking a phone number and/or e-mail address to a Threema ID is optional; when doing so, only checksum values (SHA-256 HMAC with a static key) of the e-mail address and/or phone number are sent to the server.[39] Due to the small number of possible digit combinations of a telephone number, the phone number associated with a checksum could be determined by brute force. The transmitted data is TLS-secured. The address book data is kept only in the volatile memory of the server and is deleted immediately after synchronizing contacts.[40] If a user chooses to link a phone number or e-mail address with their Threema ID, they can remove the phone number or e-mail address at any time.[41] Should a user ever lose their device (and their private key), they can revoke their Threema ID if a revocation password for that ID has been set.[42]

Groups are solely managed on users’ devices and group messages are sent to each recipient as an individual message, encrypted with the respective public key. Thus, group compositions are not exposed to the server.[43]

Data (including media files) stored on the users’ devices is encrypted with AES 256. On Android, it can be additionally protected by a passphrase.[44]

Since 2016, Threema GmbH publishes a transparency report where public authority inquiries are disclosed.[45]

On 9 March 2017 Threema was listed in the "Register of organizers of information dissemination in the Internet" operated by the Federal Service for Supervision of Communications, Information Technology and Mass Media of the Russian Federation.[46]

In a response, a Threema spokesperson publicly stated: "We operate under Swiss law and are neither allowed nor willing to provide any information about our users to foreign authorities."[47]

Architecture

The entire communication via Threema is end-to-end encrypted. During the initial setup, the application generates a key pair and sends the public key to the server while keeping the private key on the user's device.[48] The application then encrypts all messages and files that are sent to other Threema users with their respective public keys.[49][50] Once a message is delivered successfully, it is immediately deleted from the servers.[51]

The encryption process used by Threema is based on the open-source library NaCl library. Threema uses asymmetric ECC-based encryption, with 256-bit strength. Threema offers a "Validation Logging" feature that makes it possible to confirm that messages are end-to-end encrypted using the NaCl Networking and Cryptography library.[52] In August 2015, Threema was subjected to an external security audit.[53] Researchers from cnlab confirmed that Threema allows secure end-to-end encryption, and claimed that they were unable to identify any weaknesses in the implementation. Cnlab researchers also confirmed that Threema provides anonymity to its users and handles contacts and other user data as advertised.[54][55]

Reception

In February 2014, German consumer organisation Stiftung Warentest evaluated several data-protection aspects of Threema, WhatsApp, Telegram, BlackBerry Messenger and Line. It considered the security of the data transmission between clients, the services' terms of use, the transparency of the service providers, the availability of the source code and the apps' overall availability. Threema was the only app rated as 'non-critical' (unkritisch) in relation to data and privacy protection, but lost marks due to its closed-source nature.[56]

Along with Cryptocat and Surespot, Threema was ranked first in a study evaluating the security and usability of instant messaging encryption software, conducted by the German PSW Group in June 2014.[57]

As of November 2015, Threema had a score of 6 out of 7 points on the – now withdrawn and outdated – Electronic Frontier Foundation's "Secure Messaging Scorecard". It received points for having communications encrypted in transit, having communications encrypted with keys the provider doesn't have access to (i.e. having end-to-end encryption), making it possible for users to independently verify their correspondent's identities, having past communications secure if the keys are stolen (i.e. implementing forward secrecy), having its security design well-documented and having completed an independent security audit. It lost a point because its source code was not open to independent review (i.e. it was not open-source).[58]

See also
  • Comparison of instant messaging clients

References
  1. Schurter, Daniel (13 December 2012). "Die Schweizer Antwort auf WhatsApp" [The Swiss answer to WhatsApp]. 20min.ch (in German). Retrieved 5 July 2014.
  2. "‎What's New - Threema". threema.chlanguage=en-us. Retrieved 2021-02-05.
  3. "What's New - Threema". threema.ch. Retrieved 2021-02-05.
  4. "Threema Source Code on GitHub".
  5. "App Remote Protocol on GitHub".
  6. Happich, Julien (23 September 2014). "Privacy gains traction with secure messaging apps". Electronic Engineering Times Europe. Retrieved 21 December 2015.
  7. "Cryptography Whitepaper" (PDF). Retrieved October 30, 2020.
  8. "FAQ – Privacy Protection". Retrieved October 30, 2020.
  9. "What is a Threema ID?". threema.ch.
  10. "What features does Threema offer?". threema.ch.
  11. "Threema Web". Retrieved October 30, 2020.
  12. "Threema". Google Play Store. Retrieved 5 July 2014.
  13. Swiss Confederation. "Swiss company registry entry for Threema GmbH". zefix.ch. Retrieved 5 July 2014.
  14. "About - Threema: Best-Selling Chat App".
  15. "Verschlüsselte Botschaften".
  16. Metzler, Marco (28 June 2015). "Kryptografie-App Threema: Schweizer sorgen für Privatsphäre" [Cryptography app Threema: Swiss ensure privacy]. Neue Zürcher Zeitung (in German). Retrieved 8 October 2015.
  17. "Im Interview: Threema". Mailify (in German). 23 July 2014. Archived from the original on 2 August 2014. Retrieved 11 October 2015.
  18. Tanriverdi, Hakan. "Der Schlossherr". Der Freitag (in German). ISSN 0945-2095. Retrieved 11 October 2015.
  19. Price, Rob (18 June 2015). "Germany's most popular paid app is a secure messenger loved by millions — now it's taking on the US". Business Insider UK. Retrieved 11 October 2015.
  20. Dillet, Romain (21 February 2014). "Bye Bye, WhatsApp: Germans Switch To Threema For Privacy Reasons". TechCrunch.
  21. "Threema GmbH, Pfäffikon SZ". Shabex.ch. Retrieved 11 October 2015.
  22. "iOS-Highlights: Die besten Apps des Jahres" [The best apps of the year]. Focus (in German). 9 December 2014. Retrieved 1 March 2016.
  23. Cimpanu, Catalin (August 11, 2020). "Threema joins the ranks of E2EE chat apps that support encrypted video calls". ZDNet. Retrieved October 30, 2020.
  24. Cimpanu, Catalin (September 4, 2020). "Threema E2EE chat app to go 'fully open source' within months". ZDNet. Retrieved October 30, 2020.
  25. "WhatsApp-Konkurrenten verzeichnen starken Nutzeranstieg". Die Zeit (in German). 13 January 2021. Retrieved 13 January 2021.
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  31. "Big Update for Android". threema.ch.
  32. "The messenger for organizations". work.threema.ch.
  33. "Pricing Threema Work".
  34. Iseli, Marc (28 September 2015). "US-Feldzug von Threema gerät ins Stocken" [US campaign of Threema is stalled]. Handelszeitung (in German). ISSN 1422-8971. Retrieved October 12, 2015.
  35. "Threema GmbH". GitHub. Retrieved September 20, 2017.
  36. "Broadcast Blog-Post".
  37. "Threema Education: Framework Contract with educa.ch". September 10, 2020. Retrieved October 25, 2020.
  38. "Reference Sheet Privacy and Security" (PDF). threema.ch. p. 2.
  39. "Threema Cryptography Whitepaper" (PDF). threema.ch. p. 11.
  40. "Will my address book data be sent to your servers?". threema.ch.
  41. "How can I unlink my Threema ID from an email address or phone number?". threema.ch.
  42. "Revoke your ID". threema.ch.
  43. "Threema Cryptography Whitepaper" (PDF). threema.ch. p. 5.
  44. "Are messages encrypted when they are stored on my device?". threema.ch.
  45. "Transparency Report". threema.ch.
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