Partitioned Private User Storages in End-to-End Encrypted Online Social Networks

In secure Online Social Networks (OSN), often end-to-end encryption is used to ensure the privacy of the communication. To manage, store, or transfer cryptographic keys from one device to another, encrypted private storages can be used. To gain access to such storages, login credentials, only known to the user, are needed. Losing these credentials results in a permanent loss of cryptographic keys and messages because the storage is encrypted. We present a scheme to split encrypted user storages into multiple storages. Each one can be reconstructed with the help of other participants of the OSN. The more of the storages can be reconstructed, the higher the chance of successfully reconstructing the complete private storage is. Therefore, regaining possession of the cryptographic keys used for communication is increased. We achieve high rates of successful reconstructions, even if a large fraction of the distributed shares is not accessible anymore because the shareholders are inactive or malicious.