In addition to text messaging, users can make voice and video calls, send multimedia, locations, voice messages, and files. The verification level of each contact is displayed in the Threema application as dots next to the corresponding contact. Threema knows three levels of authentication (trust levels of the contact's identity). Using this strong authentication feature, 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. 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. Users can verify the identity of their Threema contacts by scanning their QR code when they meet physically. Hence, the service can be used anonymously. Linking a phone number or email address to a Threema ID is optional. It is possible to find other users by phone number or email address if the user allows the app to synchronize their address book.

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. This helps anonymize the users to a degree. The service claims to be based on the privacy by design principles by not requiring a phone number or other personally identifiable information. Threema is available on iOS and Android and has clients for Windows, macOS, Linux, and can be accessed via web browser but requires a mobile app to function. Unlike many other popular secure messaging apps, Threema does not require phone numbers or email address for registration, only a one-time purchase. Users can make voice and video calls, send photos, files, and voice notes, share locations, and make groups. The service operates on a decentralized architecture and offers end-to-end encryption.

Threema is a paid cross-platform encrypted instant messaging app developed by Threema GmbH in Switzerland and launched in 2012. ( November 2015) ( Learn how and when to remove this template message) The references used may be made clearer with a different or consistent style of citation and footnoting. This article has an unclear citation style.

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