Boxcryptor

Boxcryptor protects files in the cloud whether you use Dropbox, Google Drive, Microsoft onedrive, SugarSync, Box, or any other cloud storage. Once installed, the program creates a virtual disk drive that is linked directly to the selected cloud storage. To encrypt data, just invoke the context menu in the program on the selected folder or file. The free version of the program has some severely limited features and uses the 256-bit AES encryption algorithm.