Quantum Cryptanalysis on A5/1 Stream cipher

Abstract

In this Paper, we present Quantum Cryptanalysis on A5/1. We focus on the fundamental query, Are Symmetric Ciphers really insecure against quantum adversary? We tried to understand this question by considering A5/1 symmetric key stream cipher. The hardware implementation of symmetric key Block cipher designs under combinational circuits, where symmetric key Stream cipher, in particular, LFSR based ciphers(A5/1 etc.) circuits belong to the sequential circuit group. In this paper we presented to get a clearer view about the quantum attack on A5/1 and hence on sequential circuit. By exploiting Grover’s algorithm one can bypass the huge off-line computation required for classical Time/Memory/Data Tradeoff attack. We have been focusing on practical implementation of this quantum attack in IBM quantum computer interface. We also implemented reduced version of Quantum A5/1(10-bit) using Qiskit programming and also estimated number of gates and working qubits required for full scale implementation of A5/1 cipher.