International Association
for Cryptologic Research

The development of quantum computers, which employ a different paradigm of computation, is posing a threat to the security of cryptography. Narrowing down the scope to symmetric-key cryptography, the Grover search algorithm is probably the most influential in terms of its impact on security. Recently, there have been efforts to estimate the complexity of the Grover’s key search for symmetric key ciphers and evaluate their post-quantum security. In this paper, we present a depth-optimized implementation of a quantum circuit for ASCON, which is a symmetric key cipher that has recently been standardized in the NIST (National Institute of Standards and Technology) Lightweight Cryptography standardization. As far as we know, this is the first implementation of a quantum circuit for the ASCON AEAD (Authenticated Encryption with Associated Data) scheme. To our understanding, reducing the depth of the quantum circuit for the target cipher is the most effective approach for Grover’s key search. We demonstrate the optimal Grover’s key search cost for ASCON, along with a proposed depth-optimized quantum circuit. Further, based on the estimated cost, we evaluate the post-quantum security strength of ASCON according to relevant evaluation criteria and state-of-the-art research.