Abstract: A multi-user file storage service and system enable each user of a pre-subscribed user group to communicate with a remote file server node via a wide area network and to access the files of the file group via the respective client node. More than one user of the pre-subscribed user group is permitted to access the file group at the remote file server node simultaneously. Integrity of the files at the remote file server node are maintained by controlling each access to each file at the remote file server node so that each access to files at the remote file server is performed, if at all, on a respective portion of each file as most recently updated at the remote file server node. Additionally, an encrypted key is transferred from the file server node to a particular client node via a secure channel. The encrypted key uses an encryption function and a decryption function not known locally at the remote file server.