What are Threema calls?

Threema calls impress with crystal-clear voice quality and brilliant video quality. Since they are end-to-end encrypted, they are tap-proof. Instead of a phone number, the Threema ID serves as unique identifier.

• The call connection is established using Threema messages in the background; therefore, voice calls are just as trustworthy as chats, and the same verification levels apply
  
• If possible, a direct connection between caller and callee is established (peer to peer) after the connection buildup*
  
• Calls with verification level 1 (red) IDs are routed through the Threema server in order to obscure the IP address (in “Settings > Secure calls” (Android) or “Settings > Threema Calls” (iOS), there’s an option to route all calls through the Threema server)*
  
• Because a constant bit rate is used for audio encoding, no conclusions about the content can be drawn from the size of the transmitted data packets*
  
• Video transmission is an option of Threema calls that can be enabled at any time during an ongoing call. Once a Threema call is established, both parties can independently enable and disable video transmission by tapping the camera icon.
• Thanks to Threema’s contact verification, Man-in-the-Middle attacks can be effectively prevented, and there’s no need to manually verify a code for the purpose of authentication

*) Only applies to 1:1 calls, not to group calls.

For detailed technical information in regard to Threema calls’ security, please refer to the Cryptography Whitepaper.