Threema is a paid messenger for text messages and voice, video and group calls. The Threema Private app costs CHF 6 once and runs on Android and iPhone; a desktop app is in beta for Windows, Mac and Linux, and a web client works in the browser. Instead of a phone number, each account gets a randomly generated Threema ID.

Threema AG, the company behind the app, is based in Switzerland and runs its servers in two data centres near Zurich. At the beginning of 2026 ownership passed from the investment firm Afinum to Comitis Capital, a German private equity firm.

Threema’s strength is that it asks for no personal data and stores little on its servers: chats, contact lists and groups live on your devices. The weak point is verifiability, because the chat servers are not open source and the desktop app is still a beta.

Cryptography & Protocol

Threema uses its own messenger protocol, built on the NaCl library with Curve25519 key exchange. End-to-end encryption is on by default for private chats, media and voice and video calls. In groups each message is encrypted separately for every member and sent to each of them, and group calls are end-to-end encrypted as well.

Since December 2022 a second layer called Ibex sits on top of the base protocol. It adds forward secrecy with a ratchet that derives a new key for each message and erases the previous one. Forward secrecy has been on by default since Threema 5.1 for Android and 5.4 for iOS.

Ibex does not cover every setup. While the multi-device protocol is in use, messages have no forward secrecy; Threema’s cryptography whitepaper calls bringing it to that protocol “ongoing work in progress”. The whitepaper does not describe post-compromise security, so there is no stated way for a conversation to recover its secrecy after a key is stolen.

In 2023 three researchers from the Chair of Applied Cryptography at the University of Erlangen-Nuremberg formally proved the confidentiality, integrity, authenticity and forward secrecy of Ibex.

Metadata Privacy

Threema asks for no phone number or email. The sign-up identifier is a randomly generated 8-character Threema ID. Linking a phone number or email to the ID is optional.

Contact discovery through the address book is optional too. If you turn it on, the app uploads hashes of the phone numbers and email addresses in your contacts, and the directory server discards them as soon as it has returned the matching Threema IDs.

The servers need to know who sends a message to whom in order to deliver it. Threema says it does not log this, and it deletes each message from the server as soon as it reaches the recipient. The servers do not know which groups exist or who belongs to them. This metadata protection rests on what Threema collects and deletes, not on a network design that hides the sender from the server.

On a valid court order Threema can hand over the date a Threema ID was created, the date it last logged in, the hash of a linked phone number or email, and a push token if the app uses a third-party push service. Threema says it is below the revenue limits that trigger mandatory metadata retention under Swiss law. Its transparency report counts 423 requests from authorities in 2025, with data provided in 402 cases covering 1,505 Threema IDs; from January to 30 June 2026 there were 444 requests, with data provided in 438 cases.

Push notifications depend on the platform. On Android the app uses either Threema’s own push service or Google’s, with an empty payload. On iOS notifications go through Apple, with a payload encrypted under a key Apple does not know.

Group calls can pass through Threema media routers located abroad. These routers see the participants’ IP addresses while the call is under way, and Threema says it does not log them.

The privacy policy describes no analytics in the apps, and crash reports contain no personal data. The debug log reaches Threema only if you send it manually. In practice this means no telemetry.

Transparency & Verifiability

The Android, iOS, desktop and web apps are open source under the AGPL-3.0 license. The Android app offers reproducible builds, so you can confirm that the installed app was built from the public code. Threema says that Apple’s restrictions make this hard to offer for iOS, and the iOS app has none.

Threema runs a centralized service, and the chat, directory and mediator servers are not published. Only two side components are public: the push relay and the SaltyRTC signalling server.

Cure53 audited the source code of the mobile apps in 2020, over 16 person-days, and found no serious vulnerabilities. In January 2024 five Cure53 testers spent 16 days on the beta of Desktop 2.0. They found 7 issues, 3 of them vulnerabilities, and none rated critical or high. Between those two audits came the 2023 formal analysis of Ibex by the University of Erlangen-Nuremberg. Threema’s audit page also lists a 2019 audit by the Lab for IT Security at Münster University of Applied Sciences. No audit of the server code is listed.

Threema runs a bug bounty programme on GObugfree.

The 2023 research on Threema’s protocol

In January 2023 three researchers from ETH Zurich, Paterson, Scarlata and Truong, published “Three Lessons from Threema: Analysis of a Secure Messenger”. They described seven attacks on Threema’s cryptographic protocols, with working proof-of-concept code. The attacks assume one of three situations: an attacker on the network, a compromised Threema server, or someone forced to hand over an unlocked phone.

The researchers reported the issues to Threema on 3 October 2022 and published them on 9 January 2023. They wrote that they believe all the vulnerabilities have been mitigated by Threema’s patches, and that some may have been present in Threema for a long time. They also wrote that previous independent audits of Threema did not review the cryptographic core of the app.

The research covered the protocol before Ibex. The researchers stated that they did not audit Ibex. The paper was presented at USENIX Security 2023, and its page reports no attacks used against real users. This was research on the protocol, not a leak of user data.

Usability & Reach

On Android, Threema is available on Google Play, F-Droid, Huawei AppGallery and from the Threema Shop; on iPhone, from the App Store. Desktop App 2.0 is a beta for Mac, Windows and Linux (as a Flatpak), and the older Desktop App 1.0 is still offered. The web client runs at web.threema.ch.

Multi-device use is limited. A Threema ID cannot be used on several phones at the same time; the desktop app and the web client connect to the phone where the ID is set up.

The app is paid, and the license is tied to the store you bought it from. Moving from Android to iPhone, or back, means buying the app again.

Threema Safe is the backup for an account. It stores the Threema ID and its keys, nickname, profile picture, contacts, group memberships and some privacy settings. It does not include chats or media files.

Besides voice, video and group calls, Threema has polls, emoji reactions, editing and deleting of sent messages, and hidden chats protected by a passcode. Distribution lists are available on Android only.

Funding & Sustainability

Threema’s funding model is mixed. Individuals pay CHF 6 once for Threema Private, with no subscription and no paid extra features. Businesses pay for separate products, Threema Work and Threema OnPrem. Threema says the app price covers development and server costs, so it has no need to make money from user data.

The company has changed owners twice. In 2020 the investment firm Afinum Management bought a majority stake, and at the beginning of 2026 ownership passed to Comitis Capital GmbH, a German private equity firm. Threema says its mission, values, management, headquarters and servers stay the same and that nothing will change for users. Privacy Guides, reporting the sale in January 2026, wrote that it is unclear whether Comitis will make significant changes.

Pros and Cons

No phone number or email is needed to sign up; each account gets a random Threema ID
Private chats, groups, media and calls are end-to-end encrypted by default
The Ibex layer adds forward secrecy, formally proved by researchers at the University of Erlangen-Nuremberg in 2023
Messages are deleted from the server once delivered, and the servers do not know which groups exist
The apps are open source under the AGPL-3.0 license, with reproducible builds on Android
Cure53 audited the mobile apps in 2020 and the desktop app in 2024, finding no critical or high-rated issues in the desktop app
A one-time price of CHF 6, with no subscription and no paid extra features
Android users can install it from F-Droid or the Threema Shop without Google Play

Forward secrecy is switched off while the multi-device protocol is in use
The chat, directory and mediator servers are not open source
The iOS app has no reproducible builds
A Threema ID cannot be used on two phones at the same time, and the desktop app is still a beta
Threema Safe backups do not include chats or media files
Group calls can pass through media routers abroad that see participants' IP addresses
The license cannot be moved between Android and iPhone, so switching platforms means paying again
Since early 2026 a private equity firm owns Threema, and it is unclear whether the new owner will make significant changes

Our Rating

Cryptography & Protocol7.5/10
Private chats, groups, media and calls are end-to-end encrypted by default, and the Ibex layer adds forward secrecy that researchers at the University of Erlangen-Nuremberg formally proved in 2023. Forward secrecy is switched off while the multi-device protocol is in use, and the whitepaper does not describe post-compromise security.
Metadata Privacy7.5/10
Sign-up needs no phone number or email, and Threema says it does not log who writes to whom and does not know which groups exist. The servers still see who sends a message to whom while routing it, and media routers abroad see participants' IP addresses during group calls.
Transparency & Verifiability7.0/10
The apps are open source under the AGPL-3.0 license, the Android app has reproducible builds, and Cure53 audited the mobile apps in 2020 and the desktop app in 2024. The chat servers are not published, and the iOS app has no reproducible builds.
Usability & Reach6.5/10
Threema runs on Android, iPhone and the web, and its desktop app is still a beta. The app costs CHF 6, a Threema ID cannot be used on two phones at once, and the Threema Safe backup does not include chats.
Funding & Sustainability7.0/10
A one-time price of CHF 6 and paid business products fund Threema, with no subscription and no paid extra features. Since early 2026 a German private equity firm has owned the company, and it is unclear whether the new owner will make significant changes.

Overall7.2/10

Cryptography & Protocol 30% · Metadata Privacy 25% · Transparency & Verifiability 20% · Usability & Reach 15% · Funding & Sustainability 10%

See our rating methodology →