SECURING A PRINTHEAD IN A CLOSED SYSTEM METERING DEVICE

摘要

A closed system meter that secures the link between the accounding device (3 2) and printer (34) utilizing a Linear Feedback Shift Register (LFSR) based stream encryption is provided. The accounting device (32) includes an LFSR that comprises a plurality of stages, with one or more taps that are passed through a logic gate to provide a "feedback" signal to the input of the LFSR , to generate a pseudo-random pattern output. Preferably, a Shrinking Key Generator (SKG) is utilized to further ensure privacy of the data. The outpu t data from the accounting unit is encrypted utilizing the output from the LFS R and sent to the printing device (34). The printing device (34) includes a similar LFSR, which is utilized to decrypt the output data from the accounti ng unit (32) and enable printing.