In one embodiment, a method for securing data on a semi-trusted server is implemented on a computing device and includes: receiving at least a current session key from a user device for use during a current session, where the current session key is suitable for encrypting data and for decrypting data encrypted with the current session key, decrypting communications received from the user device during the session with said session key, encrypting with the session key at least one of communications to be sent to said user device and personal data generated during the session, storing the encrypted personal data, and discarding the current session key upon completion of the session, thereby limiting possible access to the stored encrypted personal data other than during the session. Related apparatus and methods are also described.