I am creating a php API for Android and iOS apps where I want the data to be encrypted during transmission - so that no one can view the data between the connection. But the problem is that I can't get right library for encryption and decryption for the three languages( PHP, swift, android).

Am I going in the right way? Will my API slow down because of encryption? I also think that we can go for the SSL. Is this the right approach?

Kindly suggest me.