Devices, systems, and methods of user authentication. A system includes a spatial challenge unit to distinguish between a human user and a non-human user. The spatial challenge unit requires the user to perform one or more spatial operations that modify the spatial properties of an electronic device operated by the user. Correct performance of the required spatial operations, indicates that the user is human. The system also includes a spatial password unit, which tracks a manner in which a human user handles the electronic device while the user enters a password; and then utilizes this user-specific manner for user authentication, by checking whether a manner in which the user enters his password matches a reference manner of password entry or a historical manner of password entry. The system also utilizes sequence of spatial operations or spatial gestures, as a pure spatial password or purely-spatial user-authentication factor.