The invention concerns a protected optical disk for storing data. It also concerns a method for protecting said disk. The invention is characterized in that said disk firstly comprises a portable object comprising a memory including at least one secret key, and secondly data exchange means, said key making it possible to decrypt the data of said disk whilst remaining in said portable object, said exchange means making it possible to exchange said data between said portable object and said disk. The invention can be applied in particular to CD-ROMs.