ALScA: A Framework for Using Auxiliary Learning Side-Channel Attacks to Model PUFs

Physical unclonable functions (PUFs) have emerged as potent hardware primitives owing to their intrinsic properties of being secret key-free, clone-proof, and lightweight. However, PUFs cannot avoid the threats of machine learning modeling and side-channel attacks (SCAs). Nevertheless, almost all attacks neglect the correlations between the mathematical model and side-channel models introduced by PUF internal parameters; thus, such attacks fail to exploit related data and struggle in modeling complex PUFs. To address this problem, we propose a framework for using auxiliary learning SCAs to model strong PUFs by learning multiple related tasks together. Side-channel information predictions are introduced as auxiliary tasks to facilitate the primary task of predicting response. The parameters hard for the primary task to learn can be shared by the auxiliary tasks that learn the same parameters more straightforwardly. Based on the proposed framework, we design a specific auxiliary learning power SCA that employs power level prediction as the auxiliary task. The proposed attack is implemented with the hard-parameter sharing and hierarchy sharing deep neural networks. Experimental results demonstrate that the proposed attack succeeds in modeling XOR APUF, MPUF, and iPUF and outperforms the state-of-the-art methods in modeling MPUF and iPUF. We evaluate the influences of task relatedness, architecture, and loss weight ratio. Furthermore, we propose a fine-grained classification-based method to generate the auxiliary task with an enhanced relationship to the primary task. According to the response, the class corresponding to a specific side-channel state is further divided into two subclasses. Experimental results demonstrate that the generated auxiliary task promotes performance and alleviates the adverse effects of improper architecture and parameters.