Quantum exhaustive key search with simplified-DES as a case study.

Area of Science:

• Quantum Computing
• Cryptography
• Information Security

Background:

• Evaluating symmetric cryptosystem security against quantum attacks requires quantum implementation.
• Classical block ciphers are vulnerable to quantum algorithms like Grover's search.

Purpose of the Study:

• To propose and verify a quantum implementation of a classical block cipher.
• To assess the security of this quantum cipher against quantum key recovery attacks.

Main Methods:

• Developed a quantum circuit for a classical block cipher using a polynomial number of quantum gates.
• Tested the implementation on the libquantum simulator.
• Applied Grover's algorithm as a quantum attack to recover the secret key.

Main Results:

• Verified the functionality of the quantum cipher, comparing results with the classical version.
• Demonstrated that Grover's algorithm can recover an n-bit key in O(sqrt(N)) steps, where N is the key space size.
• The quantum cipher was used as a black box for quantum search, with the oracle querying ciphertext.

Conclusions:

• The quantum implementation of the classical block cipher is feasible and verifiable.
• The study highlights the potential vulnerability of such ciphers to quantum attacks, specifically Grover's algorithm.
• This research contributes to understanding quantum security implications for symmetric cryptosystems.