35. A knowledge-based authentication server for restricting access of a user to a restricted resource, comprising: a memory; and at least one hardware device, coupled to the memory, operative to implement the following steps: challenging said user with one or more questions requiring knowledge by said user, wherein said user previously provided one or more answers to said one or more questions during a set-up phase, wherein at least one of said answers provided by said user encode one or more of historical, inter-relational and contextual information of said user using an encoding scheme defined between said server and said user to signal a fraudulent access attempt; receiving a response from said user to said one or more questions, wherein at least a portion of said response is encoded by said user using said encoding scheme defined between said server and said user to signal said fraudulent access attempt; and granting access to said restricted resource if one or more predefined response criteria are satisfied, wherein said one or more predefined response criteria comprises an assessment of whether said encoded portion of said response satisfies said encoding scheme.
35. A knowledge-based authentication server for restricting access of a user to a restricted resource, comprising: a memory; and at least one hardware device, coupled to the memory, operative to implement the following steps: challenging said user with one or more questions requiring knowledge by said user, wherein said user previously provided one or more answers to said one or more questions during a set-up phase, wherein at least one of said answers provided by said user encode one or more of historical, inter-relational and contextual information of said user using an encoding scheme defined between said server and said user to signal a fraudulent access attempt; receiving a response from said user to said one or more questions, wherein at least a portion of said response is encoded by said user using said encoding scheme defined between said server and said user to signal said fraudulent access attempt; and granting access to said restricted resource if one or more predefined response criteria are satisfied, wherein said one or more predefined response criteria comprises an assessment of whether said encoded portion of said response satisfies said encoding scheme. 42. The server of claim 35 , wherein said encoding scheme comprises determining an index based on answers of said user to a plurality of control questions, wherein said index identifies one of a plurality of possible queries that can be answered in a database containing information that is personal to the user.