Quantum-Resilient Cryptography: A Survey on Classical and Quantum Algorithms

The rapid advancement of quantum computing is poised to disrupt the foundations of classical cryptography, calling into question the long-term security of widely used algorithms. Classical cryptographic techniques, including symmetric key algorithms like DES, 3DES and AES, asymmetric schemes such as RSA and ECC, and essential primitives like hash functions and the One-Time Pad (OTP), have been the cornerstone of secure digital communication since their inception. However, the progress of quantum algorithms, spearheaded by Shor and Grover, poses serious threats to these schemes, necessitating a shift in cryptographic design. This paper presents an all-encompassing review of classical cryptographic techniques, along with emerging post-quantum cryptographic (PQC) algorithms that have been developed to provide quantum-resistant security while maintaining compatibility with classical infrastructure. Concurrently, the quantum key distribution (QKD) introduces a radical shift, leveraging quantum mechanics principles to attain unconditional security. This paper elaborates both Discrete Variable (DV-QKD) and Continuous Variable (CV-QKD) approaches, highlighting their operational principles and security models. By providing a relative analysis of classical cryptographic methods, PQC, and quantum cryptography, including QKD protocols and quantum-safe primitives, this work targets to provide a consolidated insight into modern cryptographic landscape and further research toward secure communication in the quantum era.