Patent ID: 6757832
Filing Date: 2004-06-29
Classification: G06F,G11C,H04L

Abstract:
In an authentication chip having secret information stored within it, including secret data and non sensitive data stored in multi-level flash memory, the multi-level flash memory having invalid and valid (intermediate) voltage stages, a method of protecting the authentication chip from unauthorised modification of values stored in the flash memory, the method including the steps of:using an internal command to store the secret information, including the secret data and a checksum for the data, where the secret information can only be accessed by one or more further commands; storing the secret data in intermediate states of the multi-level flash memory between the minimum and maximum voltage level states; performing a data validity check on non-sensitive data by detecting invalid states in the multi-level memory; performing a data validity check on secret data items before allowing the data items to be read out by a command accessing them, the validity check involving calculation of a checksum and comparison of the result with the checksum stored using the internal command.