Contemporary cryptographic algorithms are resistant to the strongest threats to cybersecurity and high-profile cyber-attacks. In recent times, information security scientists and researchers had developed various cryptographic schemes that defeated attacks using the most sophisticated (in terms of processor speed) classical computer. However, this resistance will soon erode with the arrival of quantum computers. In this paper, we profiled quantum computers and quantum algorithms based on their widely believed threat against currently secure cryptographic primitives. We found that Grover’s and Shor’s quantum-based algorithms actually pose a threat to the continued security of symmetric cryptosystems (e.g. 128-bit AES) and asymmetric (public key) cryptosystems (e.g. RSA, Elgamal, elliptic curve Diffie Hellman (ECDH), etc.) respectively.We discovered that the source of the algorithms’ cryptanalytic power against the current systems, stems from the fact that they (Grover and Shor) both equipped their respective algorithms with a quantum circuit component that can execute the oracle in parallel by applying a single circuit to all possible states of an n-qubit input. With this exponential level of processing characteristic of quantum computers and quantum-based algorithms, it is easy for the current cryptosystems to be broken since the algorithms can existentially solve the underlying mathematical problems such as integer factorization, discrete logarithm problem and elliptic curve problem, which formed the basis of the security of the affected cryptosystems. Based on this realization and as part of our readiness for a post quantum era, we explored other mathematical structures (lattices, hashes, codes, isogenies, high entropy-based symmetric key resistance, and multivariate quadratic problems) whose hardness could surpass the cryptanalytic nightmare posed by quantum computers and quantum-based algorithms. Our contribution is that, based on the findings of this research work, we can confidently assert that all hope is not lost for organizations heavily relying on protocols and applications like HTTPS, TLS, PGP, Bitcoin, etc., which derived their security from the endangered cryptosystems.

Recommender systems (RSs) effectively curb information overload by providing personalized suggestions of items to users across different online domains. Their widespread use in e-commerce enhances user engagement, personalizes shopping experiences, and drives sales growth. However, despite the effectiveness of these systems at generating recommendations for users, they still raise major privacy and security concerns as their data could be exploited for malicious purposes, which can lead to data breaches and misuse. Therefore, this paper presents a comprehensive and systematic review of the underlying causes of privacy and security challenges in RS. It also provides a detailed taxonomy categorizing these concerns based on their targets and the risks they create. It further presents potential solutions that have been used in the literature while identifying challenges and possible research directions to pursue in a bid to address privacy and security concerns in RSs. This paper will be a useful resource for current and upcoming researchers in the domain of RSs. It will support knowledge advancement and steer appropriate research directions.