Evaluation of Grover’s algorithm toward quantum cryptanalysis on ChaCha
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.
Bathe, Bhagwan; Anand, Ravi; and Dutta, Suman, "Evaluation of Grover’s algorithm toward quantum cryptanalysis on ChaCha" (2021). Journal Articles. 1669.