​​AWS Wickr for enterprises with auditing and regulatory requirements:

https://aws.amazon.com/blogs/aws/aws-wickr-a-secure-end-to-end-encrypted-communication-service-for-enterprises-with-auditing-and-regulatory-requirements/

End-to-End Encryption
☐ Wickr provides secure communication between two or more correspondents. It means that the system provides authenticity and confidentiality: no unauthorized party can inject a message into the system, and no unintended party can access or understand the communications without being given them by one of the correspondents.
☐ Each message gets a unique AES encryption key and a unique ECDH public key to negotiate the key exchange with other recipients. The message content (text, files, audio, or video) is encrypted on the sending device (your iPhone, for example) using the message-specific AES key. The message-specific AES key is exchanged with recipients via a Diffie-Hellman EDCH521 mechanism. This ensures that only intended recipients have the message-specific AES key to decrypt the message.

#Wickr