过分伤痛An obvious, albeit naive, alternative to the proposed metering scheme is to just add a disconnected extra piece of programmable memories which carries the ID mark of a spe-cific manufactured IC or to add extra identification code to the software. The first advan-tage of the proposed distributed and integrated within design hardware metering scheme over this straightforward scheme is that it has lower hardware overhead, since it leverages a part of don’t-care signals in the finite state machine of the hardware design or an unused state in the software program. However, since the overall overhead for both schemes is low, there is a number of much more important advantages. What is common to all these attacks is that they externally induced controllability or observability. The approach also provides some level of protection against reverse engineering. For example in hardware, the presence of programmable control path instead of hard-wired logic makes reverse engineering more difficult since essentially all reverse engineering schemes require multi-ple chips to be dissected [1, 24]. Since, now each chip is slightly different but has the same functionality, the reverse engineering process is more difficult.
Furthermore, distributed programmable resources in the control part have a number of potential positive side effects. For example, they can be used to facilitate debugging [31] and engineering change during the design phase or testing once the chip is manufactured [10].
Finally, it is interesting and important to discuss the relationship of the proposed hardware metering scheme with fingerprinting schemes for IP protection [5]. For exam-ple, fingerprinting-based metering solution is to give the manufacturer the number of IPs as stated in the licensing agreement, each IP has a unique fingerprint and implements the same functionality [20]. If the manufacturer uses one piece of IP more than once, then they face risk of being caught by the IP provider from detecting multiple copies of the same fingerprint. However, this challenges the mass foundry production line since each IP requires the unique mask and makes tuning of parameters of the foundry line to design much more difficult. Also, fingerprinting will inevitably introduce a significantly large overhead since it aims at placing hidden information in all parts of the hardware/software design and follows random signature driven constraints.
1.2 Motivational Example
To illustrate the key ideas behind the hardware metering approach, consider the sec-ond order continued fraction IIR filter [9] shown in Figure 1. For simplicity, we assume
