The present invention relates to a data carrier comprising an information layer (1) itself comprising a specific area (4) able to deliver a first optical signal and a second optical signal when illuminated by a light source. Said data carrier also comprises an additional layer (2) able to deliver an electrical signal when illuminated by the second optical signal, said electrical signal corresponding to a predetermined pattern. The combination of the first optical signal and of the electrical signal forms a cryptographic key that is required to decrypt encrypted data contained in the information layer. This invention is particularly relevant to the read out of data stored on optical discs of the Read Only Memory type.