What is ZRTP?

ZRTP is a secure transmission protocol for voice communication. The name is an acronym for Z (a reference to its inventor, Phil Zimmermann) and Real-time Transfer Protocol. Diffie-Hellman keys are generated on each session, building on each successive conversation, bolstered by the sharing of a randomly generated session secret, ensures that ZRTP is not reliant on any 3rd party authentication, such as PKI infrastructure.

ZRTP offers protection against man in the middle (MitM) attacks by having the caller and recipient to confirm a randomly generated Short Authentication String with each other. The SAS is used to authenticate the key exchange, which is essentially a cryptographic hash of the two Diffie–Hellman values. A mismatch of the numbers read to the conversation partner alerts both parties that there is a listener on the call. Because the session secret uses elements of keys from previous conversations, no listener can enter into a conversation already underway.

ZRTP offers:

  • Perfect Forward Secrecy – keys are destroyed at end of each session, preventing future calls from being compromised by previous key materials
  • Peer to Peer topology – no reliance on server or PKI infrastructure
  • MitM protection – A Short Authentication String protects the initial session from potential listeners, and future sessions are protected by key material caching from previous sessions. Without access to the initial call, the listener is barred from later sessions.

Secure Chat offers VoIP calls and keeps your communication private via ZRTP end-to-end encryption. Follow this link to learn more about the Secure Chat app and its features.

Updated on April 18, 2018

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