Equivalent Non-linear Shift Register Transformations and Espresso

Anirban Ghatak, Kaushik Sarkar, Anupam Chattopadhyay, Ambrish Awasthi, Indivar Gupta · 2026 · Research Square

DOI: 10.21203/rs.3.rs-9706347/v1 · cited by 0 works (OpenAlex) · open-access PDF

Abstract

The stream cipher Espresso was designed by E. Dubrova and M. Hell as a hardware-efficient candidate for 5G security. It has two components - a 256-bit binary non-linear feedback shift register (NFSR), with 14 feedback taps, and a 20-variable non-linear output function. However, the security of Espresso with regard to several standard cryptanalytic attacks are estimated using an alternate NFSR, which has only two feedback taps. The above analysis is based on the claim that this alternate NFSR is obtained using a transformation algorithm which preserves the output sequence of the original NFSR.

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Topics: Linear feedback shift register, Arithmetic, Shift register, Transformation (genetics), Computer science, Stream cipher

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