Chapter 5 / 5.7 / 5.7.3

5.7.3 Impact On Existing Encryption Systems

The effect of quantum computation differs across cryptographic types:

• Symmetric encryption: Algorithms such as AES are not fundamentally broken by quantum computing, but their effective key strength is reduced by Grover’s algorithm. Doubling key length (e.g., using AES-256 rather than AES-128) restores equivalent security.
• Public-key systems: RSA, Diffie–Hellman, and elliptic-curve systems will be rendered insecure once a sufficiently large quantum computer becomes available. Migration to post-quantum schemes is therefore essential for long-term confidentiality.
• Hybrid modes: During the transition period, hybrid cryptography combines classical and post-quantum algorithms—such as RSA + Kyber or ECDH + Dilithium—so that compromise of one component does not expose the session key or signature.