Security of stored data

摘要

In a processing apparatus (1) having a number of source processors (2) and stored files (4), a security circuit (6) automatically encrypts the header of files of confidential data when an authorised processor ceases to access the file. Subsequently, if an unauthorised processor attempts to access the confidential file it does not recognise it as a data file and access is not obtained. If an authorised processor attempts to access the confidential file a decryption circuit within the security circuit (6) automatically decrypts the header so that access is obtained. A cross reference table (8) is used to determine which processor may access which files.