Understanding Classical and Post‐Quantum Cryptography and Solutions
Jai Singh Arun, Ray Harishankar, Walid Rjaib · 2025
This chapter reviews classical cryptography and its applications, and shows which subset thereof is vulnerable to attacks leveraging a cryptographically relevant quantum computer. Symmetric algorithms, asymmetric algorithms, hashing algorithms, digital signatures, digital certificates, and certificate authorities are the building blocks on which solutions to real-world security problems are built. The chapter describes three key examples where these building blocks are put to work: code signing, secure communication, and data-at-rest encryption. It explores the looming threat posed by quantum computers, particularly their ability to break widely used asymmetric cryptography via Shor's algorithm while also weakening symmetric cryptography and hashing through Grover's algorithm. The chapter contrasts post-quantum cryptography with other quantum-safe technologies such as quantum key distribution and quantum random number generators, highlighting their distinct roles and deployment implications.