Post-Quantum Cryptography

Also Known As

TL;DR

Explanation

Quantum computers running Shor's algorithm can break RSA and ECC (the basis of current TLS) in polynomial time. NIST 2024 standards: ML-KEM (Kyber — key encapsulation, replaces ECDH), ML-DSA (Dilithium — digital signatures, replaces ECDSA/RSA), FALCON (compact signatures), SPHINCS+ (hash-based, conservative choice). Harvest now, decrypt later: adversaries collect encrypted traffic today to decrypt once quantum computers exist — a real threat for data that must remain confidential for 10+ years. OpenSSL 3.x with the OQS provider supports PQC algorithms.

Common Misconception

Why It Matters

Common Mistakes

• Waiting for quantum computers to appear before starting migration
• Not considering hybrid classical+PQC algorithms — use both during transition
• Using AES-128 instead of AES-256 — Grover's algorithm halves effective key size
• Hard-coded algorithm choices that make future migration difficult

Code Examples

// RSA key exchange — vulnerable to future quantum attack:
$key = openssl_pkey_new(['private_key_bits' => 2048, 'private_key_type' => OPENSSL_KEYTYPE_RSA]);
// Current security: excellent
// Security in 2035 when quantum computer exists: zero
// Data encrypted today: potentially decryptable then

// Cryptographic agility interface — enables algorithm swap:
interface KeyExchange {
    public function generateKeyPair(): KeyPair;
    public function encapsulate(PublicKey $pk): array;
}
// Today: implement with X25519 (classical)
// Migration path: swap to X25519+Kyber (hybrid)
// No application code changes needed

References

• ↗ https://csrc.nist.gov/Projects/post-quantum-cryptography

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