14 DAY TRIAL // For those that need to keep a tight rein over the people who accesses their files stored in the cloud, there is a neat solution called Cloudfogger, which is designed to offer client-side encryption for the data before it gets uploaded.
The application is free of charge and uses AES 256bit on-the-fly encryption with RSA key protection. This means that the encryption is done on your computer and then the data is uploaded in the cloud. It also works with all popular online storage services, such as Dropbox, Box, Google Drive or Microsoft’s SkyDrive.
Even if it encrypts your files, the application still allows you to share data with your friends, as long as you create a Cloudfogger account. All encrypted data is available through a virtual drive from where it can be accessed unhindered.
You can download Cloudfogger from this page.