Abstract: An apparatus for determining the identity or authenticity of a document and/or the identity of a user of a document to determine if such person is authorized to do so, and which document is formed as a data carrier, comprising readers for data which can be automatically read and applied to the document. A keyboard or equivalent structure is provided for the infeed of a secret code, such as a number(s), letter(s) or other characters, as is also an evaluation circuit. The evaluation circuit comprises a fixed storage where there can be stored constant data and data processing programs, an access circuit which evaluates parts of the automatically readable data of the document and/or the secret code written in by means of the keyboard in the form of select addresses.