Securing IEEE 1687-2014 Standard Instrumentation Access by LFSR Key

IEEE 1687-2014 Standard provides an effective method for accessing on-chip instruments for testing, debugging and board configuration. The standard, however, causes a safety problem because anyone can access the chip instruments, set inputs and obtain safety critical information. In recent work, a lock in the segment insertion bit (SIB) and a corresponding unlocking key application procedure have been proposed for securing the 1687. This paper provides a linear feedback shift register (LFSR) based key generation mechanism that enhances the security of 1687 very significantly. By reconfiguring m (a small number) scan flip-flops into an LFSR that generates the key to unlock the SIB, we show a substantial increase in the expected break-in time.