Evaluation of Grover’s algorithm toward quantum cryptanalysis on ChaCha

Article Type

Research Article

Publication Title

Quantum Information Processing


In this work, we have analyzed ChaCha against Grover’s search algorithm. We designed a reversible quantum circuit of ChaCha and then estimated the resources required to implement Grover. We showed that for MAXDEPTH = 2 40, the ChaCha20 256-bit key can be recovered using Grover’s search algorithm with a gate count of 1.233 · 2 251, which is less than the NIST’s requirement of 2 258. We also showed that implementing Grover’s algorithm greatly depends on the number of rounds in ChaCha. We deduced that ChaCha would require approximately 166 rounds so that implementing a non parallelized Grover would require a 2 298 gate count. We implemented a ChaCha-like toy cipher in IBMQ simulator and recovered key using Grover’s algorithm.



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