The "Top Secret" level applies an End-To-End security model, with audio model encrypts audio data encrypted on one end point of the call and decrypted it decrypts audio stream on the other end point one without any possibility to intercept it in the middle. middle point exchange. When using End-to-End Security model,

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relies on ZRTP protocol so there is no need to deploy a any PKI infrastructure, but a it's required human verification is required on each call, so to exclude the presence of a possible MITM (Man In The Middle) attacker.

Verifying call security

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Professional uses an encryption and security system based on ZRTP protocol. This protocol is based on " human " verification of two words (called Short Authentication String or SAS) displayed at the beginning of a call. The SAS are made up of two words in English, randomly generated for each call. The same SAS displayed on the two phones must be verbally compared by the two callers to guarantee call security. After the security was verified the two peers could trust each other.

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