Patent ID: 8351609

Claim:
A method for invalidating an encryption/decryption key stored in a key storage file and used for encrypting/decrypting a content file, said content file comprising a header portion containing location information which indicates the location of the key in the key storage file, by means of a key navigation file containing status information that indicates whether the key stored in the key storage file is valid or not, comprising: performing the following in a memory device configured to communicate with a host device: opening the key navigation file; finding in the key navigation file an entry which does not correspond to a location of a valid key in one or more key storage files; generating the encryption/decryption key; encrypting/decrypting the content file with the encryption/decryption key; storing the encryption/decryption key at the location in the one of the key storage file(s) corresponding to the entry; obtaining from the header portion of the content file, location information of the key in the key file; locating the status information of the key in the key navigation file using the location information; altering the status information of the key in the key navigation file to indicate that the key is invalid; and obtaining, from location of said entry in the key navigation file, key navigation information for the content file; said method using a plurality of key storage files each having m entries, wherein the key navigation information comprises an index which has a different value for each entry in the key navigation file, said method further comprising finding the location in the one or more key storage files corresponding to the entry for storing the encryption/decryption key, wherein said finding includes dividing the index by m to obtain a quotient, to obtain an integer equal to the integer portion of the quotient, and an offset equal to the remainder portion of the quotient.