Quantum computing matters for security in two opposite ways. Shor's algorithm could break the public-key encryption we rely on today, while quantum mechanics itself can be used to protect communication. This module covers both sides, then looks at what quantum computers are realistically good for.
It starts with quantum key distribution: the BB84 and E91 protocols, and why measuring a quantum state reveals an eavesdropper. Next it covers the threat to RSA from Shor's algorithm and the "store now, decrypt later" problem, followed by post-quantum cryptography, the new lattice-based and hash-based schemes designed to resist quantum attacks. It closes with the applications where quantum computers may genuinely help, from simulating molecules to optimization.
Watch the lessons in order, then put it all into practice in the course Projects.
How photon polarization can be used to share a secret key: the BB84 protocol, the no-cloning theorem, quantum networks, and Ekert's entanglement-based E91 protocol.
Veritasium on how Shor's algorithm breaks RSA, the "store now, decrypt later" threat, and the lattice-based schemes chosen by NIST to replace it.
Computerphile on Grover's and Shor's algorithms, the NIST standardization effort, lattice-based and hash-based schemes, and hybrid key exchange already used on the web.
IBM's lesson on how problems are classified by difficulty, why only some suit quantum computers, and recent examples in simulation, optimization, and finance.