Trustworthy Hardware Design: Combinational Logic Locking Techniques by Muhammad Yasin & Jeyavijayan (JV) Rajendran & Ozgur Sinanoglu

Author:Muhammad Yasin & Jeyavijayan (JV) Rajendran & Ozgur Sinanoglu
Language: eng
Format: epub
ISBN: 9783030153342
Publisher: Springer International Publishing

When the foundry is trusted and protection is required only against malicious end-users, the tree inputs may be camouflaged by inserting INV/BUF camouflaged gates at each of the tree input. Figure 5.5 also shows the camouflaging counterpart of the locked AND-tree.

5.4.1 Security Analysis

The security of ATD is dictated by the size of the largest non-decomposable tree in the circuit, i.e., a tree where all internal nodes have a fan-out of one. If the internal nodes of a tree have multiple fan-outs, an attacker can partition the tree into subtrees and target the subtrees on an individual basis. An example non-decomposable AND-tree and a decomposable tree is presented in Fig. 5.6a, b, respectively. To achieve sufficient security against the SAT attack, large non-decomposable AND/OR-trees, e.g., with 64 or 128 inputs, are required. Such large trees are rare in common benchmark circuits. We elaborate on this in Sect. 7.​3. For the upcoming discussion in this section, we assume that non-decomposable AND-trees exist in a netlist. Furthermore, we assume that all the tree inputs are primary inputs, representing the best possible security achievable by ATD.

Fig. 5.6(a) A non-decomposable AND-tree, and (b) a decomposable AND-tree [1]. Attacks on the decomposable tree can leverage divide-and-conquer strategies

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