You are designing a mobile chat application. You want to ensure people cannot spoof chat messages, by providing a message were sent by a specific user. What sho...

You are designing a mobile chat application. You want to ensure people cannot spoof chat messages, by providing a message were sent by a specific user.
What should you do?

A. Tag messages client side with the originating user identifier and the destination user. B. Encrypt the message client side using block-based encryption with a shared key. C. Use public key infrastructure (PKI) to encrypt the message client side using the originating user's private key. D. Use a trusted certificate authority to enable SSL connectivity between the client application and the server.