Dropbox: On-the-fly Encryption for cloud storage...
BoxCryptor encrypts your files using the AES-256 standard. This makes your data secure - no matter which cloud storage provider you use.
Access your encrypted files on all devices. We have BoxCryptor for Windows, Android and iOS - and even support Mac OS X and Linux.
Encrypt your files the quick and easy way. Each file is encrypted individually in real-time and stored in a folder of your choice, e.g. your Dropbox folder.