In the last years, Physical Unclonable Functions (PUFs) became a popular security primitive, which is nowadays also used in several products. As a lightweight solution for key storage, they are frequently suggested in an environment where attackers have direct access to the hardware. This triggered the evaluation of PUFs regarding side-channel weaknesses and the development of corresponding countermeasures. One primitive to overcome such attacks is the Interleaved Challenge Loop PUF (ICLooPUF). While the first analyses seem to support the resilience of this novel PUF against side-channel attacks, we identify in our work two leakage sources: First, we show that a yet unreported weakness of the counters used to measure the ICLooPUF period lengths allows for an attack. Second, we show that interleaving can be considered a modulation. As a consequence, the PUF leaks via its sidebands of the power spectrum in the frequency domain. Theoretical analysis provides an understanding of the root cause of the leakage; Practical experiments show the significance of the leakage sources and the feasibility of the attack. Potential countermeasures and the impact on the Loop PUF and its derivatives are discussed.     «

In the last years, Physical Unclonable Functions (PUFs) became a popular security primitive, which is nowadays also used in several products. As a lightweight solution for key storage, they are frequently suggested in an environment where attackers have direct access to the hardware. This triggered the evaluation of PUFs regarding side-channel weaknesses and the development of corresponding countermeasures. One primitive to overcome such attacks is the Interleaved Challenge Loop PUF (ICLooPUF)....     »