Home/Cryptography/Post-Quantum

Post-Quantum Cryptography

Preparing for Quantum Computers

12 min read Updated 2024

The Quantum Threat

Quantum computers can break RSA and ECC using Shor's algorithm. When large-scale quantum computers exist, current public-key cryptography becomes useless.

!

Harvest Now, Decrypt Later: Adversaries are storing encrypted data today, waiting to decrypt it when quantum computers are available. Long-term secrets need post-quantum protection NOW.

NIST Standards (2024)

ML-KEM (Kyber)

Key encapsulation based on lattices

Key Exchange

ML-DSA (Dilithium)

Digital signatures from lattices

Signatures

SLH-DSA (SPHINCS+)

Hash-based signatures

Signatures

Approach Categories

Lattice-basedMost promising, basis for Kyber/Dilithium
Hash-basedWell-understood security (SPHINCS+)
Code-basedMcEliece - large keys but proven
Isogeny-basedSIKE broken in 2022, research continues
MultivariateBased on solving polynomial equations

Migration Strategy

  • Inventory cryptographic dependencies
  • Use hybrid approaches (classical + PQ)
  • Signal already supports PQXDH
  • Chrome/Firefox testing PQ in TLS
  • Prioritize long-term secrets first
  • Test performance impacts

Symmetric Crypto Status

Good News
AES-256: Safe (Grover's algorithm halves security)
SHA-256: Safe with 256-bit output
ChaCha20-256: Safe

Just double key sizes for equivalent security!