Classical PKI vs Post-Quantum PKI

The core PKI trust model remains the same, but the cryptographic primitives change. Classical PKI relies on RSA and ECC for key exchange and digital signatures, which are vulnerable to quantum attacks. Post-Quantum PKI replaces or augments these with quantum-resistant algorithms such as ML-KEM and ML-DSA. This shift affects key sizes, certificate structures, validation performance, storage requirements, and interoperability across PKI components.

Certificate lifecycle management becomes more critical with PQC. Larger keys and signatures increase processing costs, making long-lived certificates less desirable. Organizations are expected to shorten certificate lifetimes, automate issuance and renewal, and improve visibility into certificate usage. PKI systems must support faster rotation, scalable revocation mechanisms, and automated monitoring to manage the increased operational load.

No. The industry is moving toward hybrid PKI, where classical and post-quantum algorithms are used together. Hybrid certificates or hybrid key exchanges ensure security even if one algorithm is later compromised. This approach provides backward compatibility, aligns with NIST and NSA guidance, and allows organizations to transition gradually without breaking existing trust relationships.

Post-quantum algorithms use significantly larger public keys and signatures than RSA or ECC. For example, an ECC public key may be only a few dozen bytes, whereas a PQC public key or signature can be several kilobytes. This increases certificate sizes, TLS handshake payloads, OCSP responses, and log storage. PKI systems must therefore handle higher bandwidth usage, larger databases, and increased memory consumption.

• In TLS, PQC primarily affects key exchange and authentication, increasing handshake sizes and potentially latency.
• For code signing and document signing, larger signatures affect storage, transmission, and verification times.
• Long-term validation (LTV) becomes more important, as documents and binaries must remain verifiable even after classical algorithms are deprecated.
• PKI architectures must adapt to ensure performance and compliance are maintained.

Partially. Core PKI concepts such as CAs, trust anchors, and certificate chains remain valid, but many components require upgrades. Cryptographic libraries, HSMs, CAs, and validation services must support PQC algorithms and hybrid modes. Systems that are crypto-agile can adapt more easily, while legacy or hard-coded environments may require replacement or significant redesign.