Kryptochat is a secure messaging app based on military-grade encryption.
The available features are:
Encrypted One-to-One Messaging
Encrypted Group Messaging
Encrypted Audio Messages
Audio, Video, File Transfer
GPS Location Sharing
Encrypted Voice Calls (*)
Encrypted Video Calls One-to-One(*)
Encrypted Audio Conferencing One-to-Many (*)
Kryptochat uses a military-grade encryption of the level RSA 8192 bit for asymmetric encryption, AES 256-bit algorithm for symmetric encryption and SHA-512 for signature algorithm.
Kryptochat also uses protocols like Transport Layer Security (TLS), Off The Record (OTR) Protocol for chat, ZRTP for VOICE, and other security features like certificate pinning on dedicated Certification Authority.
The app does not access to your contacts list, it keeps a dedicated directory in its encrypted storage.
(*) it does need "Kryptotel - Secure Voip" installed.