Migrating to Post-Quantum Cryptography

Scope and Authorization: This skill describes defensive cryptographic-migration engineering on systems you own or operate. Cryptographic discovery scanning can touch sensitive key material and production traffic — run inventory tooling only with authorization and in line with your organization's change-management and data-handling policies.

Overview

A cryptographically relevant quantum computer (CRQC) running Shor's algorithm will break the public-key cryptography that secures almost all of today's communications and signatures: RSA, finite-field and elliptic-curve Diffie-Hellman (DH/ECDH), and ECDSA. Symmetric primitives (AES) and hashes (SHA-2/3) are only weakened (Grover gives a quadratic speedup, mitigated by larger key/output sizes), but asymmetric algorithms are catastrophically broken. The most urgent threat is harvest-now, decrypt-later (HNDL): adversaries capturing encrypted traffic today to decrypt once a CRQC exists, which puts long-lived secrets (health records, state secrets, intellectual property, root-of-trust keys) at risk now.

On 13 August 2024 NIST finalized the first post-quantum standards: FIPS 203 (ML-KEM, Module-Lattice KEM, formerly CRYSTALS-Kyber) for key establishment, FIPS 204 (ML-DSA, Module-Lattice digital signatures, formerly CRYSTALS-Dilithium), and FIPS 205 (SLH-DSA, the stateless hash-based signature scheme SPHINCS+). The migration playbook (NIST SP 1800-38, Migration to Post-Quantum Cryptography) is: (1) build a cryptographic inventory / CBOM, (2) prioritize by HNDL exposure and crypto-agility, (3) deploy hybrid schemes (a classical algorithm AND a PQC algorithm combined, e.g. X25519MLKEM768) so a break in either leg does not compromise the session, and (4) re-key and rotate.

This skill maps to ATT&CK T1573 – Encrypted Channel: the same cryptographic channels adversaries abuse for stealthy C2 are the channels defenders must make quantum-resistant; understanding the algorithms in use is foundational to both attack detection and defensive migration. The NIST CSF outcome is PR.DS-02 (data-in-transit protection) — and by extension data-at-rest for HNDL-sensitive stores.

When to Use

• When building an enterprise cryptographic inventory / Cryptography Bill of Materials (CBOM) for quantum-readiness.
• When prioritizing which systems must migrate first based on data lifetime and HNDL exposure.
• When enabling hybrid post-quantum key exchange (X25519MLKEM768) on TLS endpoints, VPNs, or SSH.
• When issuing PQC or hybrid certificates and testing PQC signature verification.
• When evaluating crypto-agility — the ability to swap algorithms without re-architecting applications.