How do they offer so much storage for free? By sharing duplicates rather than uploading them over and over. At least Google uses the sharing technology as a feature. Steve
Dropbox saves storage space by analyzing users’ files before they are uploaded, using what’s known as a hash — which is basically a short signature of the file based on its contents. If another Dropbox user has already stored that file, Dropbox doesn’t actually upload the file, and simply “adds” the file to the user’s Dropbox.
The keys used to encrypt and decrypt files also are in the hands of Dropbox, not stored on each user’s machines.
