An optical card apparatus including a recording device for recording in each of a plurality of data blocks in a card-like recording medium user data to be recorded along with data protecting information inhibiting the user data from being carelessly read out, and a reproducing device for reproducing...http://www.google.de/patents/US5311498?utm_source=gb-gplus-sharePatent US5311498 - Recording and reproducing apparatus provided in each data block with a secret information number
