International Association
for Cryptologic Research

The ARADI block cipher is developed by the U.S. National Security Agency (NSA) as part of its efforts to design secure and efficient cryptographic algorithms. In this paper, we present the first detailed analysis of the lightweight block cipher ARADI under differential fault attacks. Although ARADI is structured around word-wise operations, its security fundamentally depends on bit-level properties, making it vulnerable to carefully crafted fault models. Bit-based fault models require a large number of faults, while word-based models reduce the number of faults but make precise identification of fault locations difficult. To overcome these limitations, we introduce a new nibble-based approach using permissible nibble differences (PNDs). This model provides an effective tradeoff between the number of required faults and the complexity of identifying fault positions. In our attack, the adversary randomly injects nibble faults before the last two rounds and constructs differential equations involving unknown key variables without knowing the exact fault values. Our results demonstrate that, with at most 108 random fault injections, the entire master key of ARADI can be recovered within a practical time complexity. This work reveals previously unexplored vulnerabilities of ARADI under fault attacks and highlights the need to evaluate lightweight cipher designs using nibble-level fault models, along with the traditional bit- and word-level analyses.