Nonvolatile memory unlock for an electronic postage meter

Abstract

An electronic postage meter is disclosed which includes one or more nonvolatile memories (NVM) for storing a hierarchy of secure data including the meter's unique serial number, accounting information, and various parameters which define its operating characteristics. The portion or portions of NVM containing the serial number and the aforementioned information and parameters may be totally or partially 'locked' by firmware that causes one or more 'lock bits' to be set. The setting of the lock bits is designed to prevent unauthorized access to a program which can alter the contents of predetermined portions of NVM. The disclosed postage meter is further operable to enable authorized personnel to 'unlock' said program in order to initialize, modify and/or reconfigure the meter both during the manufacturing process and after the meter has been placed in the field. Once authorized changes have been specified the meter is operative to verify that proper values have actually been placed in NVM and then relock the memory. The disclosed methods and apparatus eliminate the need to physically remove NVM in order to accomplish initialization, modification and/or reconfiguration by providing controlled access to all or part of the memory storing the hierarchy of secure data.