Jack Wallen/ZDNET Follow ZDNET:  Add us as a preferred source  on Google. ZDNET's key takeaways Encrypting files on Android is easy. You can encrypt and decrypt files with this simple app. OpenKeyChain is free to use and open-source. If you take mobile security seriously (and you should), then you might want to consider file encryption. I'm not talking about saving a file in an encrypted folder to tuck it away from prying eyes.  No. This is all about encrypting files that you can either leave on your device and view when needed or share with others, knowing they can be viewed only by the recipient. This is made possible by the OpenKeyChain app. This app is all about encryption, and although it makes the process easy, there are some things you'll need to know before diving in. Let's do just that. It's all about keys If you've ever used public key encryption on your desktop to securely send a file to someone, you already understand it. If not, let me explain.…