Hardware Obfuscation of Digital FIR Filters

Hybrid Protection of Digital FIR Filters

“…Although there exist many efficient high-level and behavioral obfuscation methods proposed for protecting IPs [8]- [13], digital FIR filters require specialized obfuscation techniques, since they should behave according to their specifications, such as passband and stopband frequencies and ripples [14]. However, there exist only a limited number of techniques proposed to obfuscate DSP circuits and especially, digital filters [15]- [18]. The technique of [15] generates the desired filter and also its obfuscated versions, grouped in two categories as meaningful and unmeaningful in terms of filter behavior, using high-level transformations, and combines these realizations using a key-based finite state machine and a reconfigurator.…”

“…To make the reverse engineering of coefficients harder for an end-user, adding input and output noises was proposed in [16]. Recently, we introduced a hardware obfuscation technique that hides the filter coefficients behind decoys [17], [18]. In [17], decoys can be selected based on their Hamming distance to reduce the hardware complexity or chosen randomly to increase the corruption at the filter output.…”

“…In [17], decoys can be selected based on their Hamming distance to reduce the hardware complexity or chosen randomly to increase the corruption at the filter output. Since an obfuscated FIR filter may still generate the desired behavior under a wrong key in [17], decoys are selected in such a way that the obfuscated filter presents the desired behavior only when the secret key is provided in [18]. To do so, the lower and upper bounds of each filter coefficient are found and decoys are selected beyond these bounds.…”

“…To do so, the lower and upper bounds of each filter coefficient are found and decoys are selected beyond these bounds. In [17], [18], the folded design of an FIR filter is considered as a case study and its Time-Multiplexed Constant Multiplication (TMCM) block is obfuscated at Register-Transfer Level (RTL).…”

“…In this article, we initially introduce the query attack, which can discover the original filter coefficients hidden behind decoys [17], [18] or replaced by key bits [9]. Then, we propose a hybrid technique, which includes both hardware obfuscation and logic locking, for the protection of digital FIR filters.…”