Abstract: Various embodiments of a system and method for backing up a plurality of copies of a file are described. A first copy of the file may be owned by a first user, and a second copy of the file may be owned by a second user. The file is split into a plurality of segments, and each segment is encrypted with a respective segment key. Each encrypted segment is transmitted to and stored on a server computer system. De-duplication techniques are used to ensure that only a single instance of each encrypted segment is stored. The segment keys used to encrypt the file segments are also stored on the server computer system in an encrypted form. De-duplication techniques may be utilized so that only a single instance of the encrypted segment keys is stored.