1. End of the Road for RSA, ECC, DH by Shor’s Algorithm
Quantum computers running Shor’s algorithm can break the mathematical problems at the foundation of most public-key systems in use today:- It factors 2048-bit RSA keys in polynomial time.
- It solves the discrete logarithm problem for Diffie-Hellman and elliptic-curve cryptography.
2. Symmetric Ciphers and Hashes Lose Half Their Security Strength, Grover’s Algorithm
Grover’s algorithm speeds up brute-force searches, like guessing AES keys or reversing hash functions, by giving a quadratic speed-up. The result:- AES-128 drops from 128-bit to 64-bit security.
- AES-256 drops to 128-bit security, still acceptable for most data in the long term.
3. The New Ecosystem: Post-Quantum Cryptography (PQC)
To replace vulnerable public-key systems, researchers are standardizing a fresh set of algorithms that resist both classical and quantum attacks. By August 2024, NIST finalized its first three PQC standards:- CRYSTALS-Kyber (now called ML-KEM): general encryption / key encapsulation (TLS, e-mail, VPN).
- CRYSTALS-Dilithium (ML-DSA): lattice-based digital signatures.
- SPHINCS+ (SLH-DSA): hash-based backup signature method (NIST, Fortinet).
4. What This Means in Practice
Store-now-decrypt-later
Encrypted data intercepted today, no matter how strong, could be recorded and later decrypted once a quantum-capable adversary obtains a working machine. Critical organisations handling health, government, intellectual property, and legal data must act now.Crypto agility and migration
- Start migrating TLS, VPN, SSH, and document signing systems to PQC-hybrid and eventually PQC×PQC modes.
- Hybrid mode (e.g. combining X25519 with Kyber in a key agreement) is seen as prudent; Signal’s PQXDH protocol is an example (Wikipedia).
- Vendor tools such as OpenSSL 3.2 and Windows 2025+ are including PQC algos.
5. Physical Security of Keys: Quantum Key Distribution (QKD)
While PQC protects the math, QKD offers complimentary protection at the physical layer:- Quantum key distribution encodes keys into photons so any eavesdrop attempt is detectable.
- In April 2025, Toshiba Europe demonstrated twin-field QKD over 254 km of standard fibre between Frankfurt and Kehl, without cryogenic cooling (Tech Monitor, spectrum.ieee.org).
- UK start-up KETS is embedding QKD modules inside telecom switches in BT’s test network (Tech Monitor).
6. Updating Common Algorithms , What to Do Now
| Algorithm / Protocol | Status Today | Quantum-Safe Replacement |
|---|---|---|
| RSA-2048 or ECDSA/ECDH | Broken by Shor’s algorithm | Use Kyber (key exchange), Dilithium or SPHINCS+ (signatures) |
| AES-128, MD5/SHA-256 | Weakened by Grover’s algorithm | Move to AES-256, SHA-384 or SHA-512 |
| Diffie-Hellman handshakes | Compromised by quantum attackers | Migrate to PQKEM like Kyber or hybrid approach |
| Digital Signatures | Falsifiable by quantum forgers | Use PQ signature schemes: Dilithium, FALCON, SPHINCS+ |