Post-Quantum Cryptography
Also known as: PQC, Quantum-Resistant Cryptography
Definition
A family of cryptographic algorithms — including lattice-based, hash-based, and code-based schemes — designed to resist cryptanalysis by both classical and quantum computers, intended as an algorithmic replacement for RSA and elliptic curve cryptography within existing protocol and public key infrastructure frameworks.
Key Points
- Unlike quantum key distribution, PQC requires no quantum hardware — it runs entirely on classical computers and integrates into existing protocols (TLS, certificate infrastructure) as an algorithm substitution
- Standardized by NIST through a multi-year public evaluation process, with the first finalized algorithm standards published in 2024
- Most PQC algorithms have significantly larger key and signature sizes than RSA or elliptic curve equivalents, a real bandwidth and storage cost for constrained or high-frequency-handshake environments
- Migration is typically implemented as a hybrid approach — combining a classical algorithm with a post-quantum algorithm in the same handshake — to hedge against undiscovered weaknesses in newer PQC schemes during the transition period
- Directly addresses the "harvest now, decrypt later" threat model by protecting today's encrypted traffic against future quantum decryption, independent of when a cryptographically relevant quantum computer actually arrives
Concept
PQC does not change how PKI is architected — certificate authorities, trust chains, and key exchange handshakes remain structurally the same — it changes which mathematical algorithm underlies the keys and signatures those structures carry. A certificate signed with a PQC algorithm slots into the same X.509 certificate format and TLS handshake process as an RSA-signed certificate; the difference is invisible at the architectural level and consequential only in the underlying math's resistance to quantum attack.
Explainer
The primary operational friction PQC introduces is size, not incompatibility: most standardized lattice-based algorithms produce keys and signatures several times larger than their RSA or elliptic curve counterparts, which matters directly for bandwidth-constrained links and high-frequency handshake scenarios — a satellite link renegotiating a PQC-based TLS session pays a real, measurable bandwidth cost per handshake that a classical algorithm would not. This is why most production PQC deployments today use a hybrid approach, running a classical and a post-quantum algorithm side by side in the same handshake, accepting the larger overhead as insurance against the currently unlikely but non-zero possibility that a newer, less-studied PQC algorithm has an undiscovered classical weakness. For CE verticals, PQC migration is a practical near-term action independent of when quantum computers actually mature: government and defense systems, along with critical energy and industrial control infrastructure carrying long-lifetime sensitive configuration data, are the highest-priority migration candidates precisely because "harvest now, decrypt later" risk accrues today, while lower-sensitivity, short-lifetime commercial traffic can reasonably defer migration further given the real bandwidth and compatibility costs involved.
Cite this entry
Post-Quantum Cryptography. ConnectedEarth Knowledge Base. https://connectedearth.space/knowledge-base/post-quantum-cryptography/ (updated 13 September 2026).