Stateless leakage resiliency from NLFSRs

Stateless cryptographic functions are required whenever the two communicating parties are not synchronized (have no memory of previous connection). It is widely accepted that these functions can only be efficiently secured against Side-Channel Analysis (SCA) using the regular countermeasures (masking and hiding). On the other hand, leakage resiliency tries to design new cryptographic functions with inherent security against SCA attacks. Generally, there are two methods to design stateless leakage resilient functions: tree structures and key-dependent algorithmic noise. Unfortunately, the first method is computationally intensive, while the current designs under the second method offer low security guarantees. In this paper, we follow the second approach to design a stateless leakage resilient function using non-linear feedback shift registers (NLFSRs). Our results show that the uncertainty on an n-bit key after any SCA attack exceeds n/2 bits, the birthday boundary, and can approach n bits, the brute-force boundary. We validate security of our structure with mathematical models and Monte Carlo simulation at noise-free conditions.