Abstract In this paper, we analyse the impact of the HHL quantum algorithm on stream ciphers in a black-box setting. We assume a black-box access to an oracle
MS M S defining the output of the stream cipher. For a state k encapsulating the key material, the value
MS⋅k M S · k is the keystream
(k1′,k2′,...,kN′) ( k 1 ′ , k 2 ′ , . . . , k N ′ ) generated by some stream cipher S. We translate this scenario into the quantum setting and describe how the HHL algorithm could be used to attack this construction. Further, we give simple and verifiable criteria under which a black-box attack on stream ciphers with the HHL algorithm is not efficiently feasible. Usually, these criteria follow from already known design principles for symmetric ciphers and should apply to the ciphers used today. We complement the criteria with a simple test, which confirms the resistance of said cipher. Moreover, we use our technique to test the currently used stream ciphers: Trivium, HC-128, and Salsa20.
This paper is the part-II of the previous paper and introduces the world of Yuen's concept. In the theory of cryptology, the Shannon impossibility theorem states that the upper bound of the security of a plaintext against a ciphertext-only attack is the entropy of the secret key. At the same time, it gives the upper bound of the unicity distance against a known plaintext attack. Hence the development of a new symmetric key cipher requires finding a way to undo or lift this theorem. Such challenges have been attempted with quantum stream cipher and quantum data locking as block cipher. Both ciphers are designed by means of differentiating the receiving performance of Bob with key and Eve without key according to the principle of quantum communication theory. Thus, the origin of security of both ciphers come from the principle of keyed communication in quantum noise (KCQ) proposed by Yuen. In this paper, we explain and compare the principles and features of both cipher and assist to improve the quantum data locking scheme. Then we will introduce experimental research on quantum stream cipher towards commercialization, which has performance superior to conventional cipher.
A quantum noise stream cipher scheme (QNSC) based on triangular quadrature amplitude modulation (TQAM) and the secret probabilistic shaping (SPS) is studied. Compared with rectangular quadrature amplitude modulation (QAM), TQAM is a more compact symmetrical structure, which results in better transmission performance and greater noise masking number. Then, SPS is realized, where the probabilistic shaping information as the secret key is masked into noise and transmitted with the encrypted signal simultaneously. The combination of SPS and QNSC makes it impossible for an attacker to obtain the ciphertext, which enhances the security of QNSC scheme without introducing additional key. TQAM and probabilistic shaping improve the transmission performance of QNSC scheme. Under 7% forward error correction (FEC) threshold in back-to-back system, compared with QAM/QNSC systems, TQAM/QNSC provides an OSNR gain of ∼ 0.6 dB, and SPS-TQAM/QNSC provides an OSNR gain of ∼ 1.2 dB. The proposed scheme is demonstrated with the net data rate of 34.28 Gbit/s over 140 km single-span standard single mode fiber.