Encryption / Decryption of contents on Android / IOS, classed needed

I need to secure contents on Android and IOS devices. To do this i want to - encrypt images, html, PDFs and other file data on Linux - decrypt this contents on Android and IOS again. I need you provide an encryption mechanism which runs on Linux and encrypts the data - provide classes for Android and for IOS to allow on-the-fly decryption. The target is to provide a minimum of security and a maximum of decryption speed. The main aim is to obfuscate the contents on Android devices so that a user cannot access the data. The classes need work like I can pass the local file location to the class as a parameter Lets discuss details on how you would approach this thru messages.