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Post-Quantum Cryptography

Post-quantum cryptography is public-key cryptography designed to resist attacks from both conventional and future large quantum computers. It replaces quantum-vulnerable key establishment and digital signatures while continuing to run on ordinary computers and networks.

itIdentity, access, and cryptography

Don't Panic — Post-Quantum Cryptography

Post-quantum cryptography is public-key cryptography that runs on ordinary computers while resisting attacks from both conventional and quantum machines. It replaces the key-establishment and signature algorithms that a future quantum computer could break — not symmetric encryption, not hashing, not your entire cryptographic stack.

The surprise for most people is that the deadline is not "when quantum computers arrive." An attacker who records your encrypted traffic today can attempt to decrypt it later. This harvest-now-decrypt-later risk means migration begins before any quantum computer exists, because the data you are encrypting tonight may still need to be confidential in ten years.

Everything else hangs off three ideas. First, NIST's standards separate two distinct jobs: ML-KEM establishes shared secrets, and ML-DSA and SLH-DSA handle signatures. A KEM is not a signature. Mixing them up is the fastest way to build a system that protects the wrong thing. Second, you replace one layer at a time — but every layer depends on the ones above and below it. Swapping a key-exchange algorithm does not fix a quantum-vulnerable certificate signature. Third, cryptographic agility — the ability to swap algorithms by configuration rather than recompilation — is what turns a decade-long crisis into a manageable program.

Here is the thing that will surprise you: this is a deployment problem wearing a cryptography costume. The algorithms were chosen in 2022 and standardized in 2024. The hard part is that post-quantum keys and signatures are much larger than their classical predecessors. Hybrid TLS handshakes can exceed 15 KB. Middleboxes drop them. Hardware security modules need replacement before they can hold the new key formats. Certificate chains built with post-quantum signatures can exceed 10 KB. None of these are problems with the mathematics. They are engineering problems with real systems that assumed cryptographic inputs would always be small.

And here is the part nobody tells you: PKI has to move before applications can. Applications consume certificates. Certificates come from infrastructure. Infrastructure depends on hardware modules that may need firmware updates or physical replacement. The dependency chain runs deeper than most migration plans account for.

The Landscape tab shows the products and vendors operating in this space. The Timeline tab traces the years-long standardization process that got us here. The Field Notes tab carries the hard-won judgments from teams who have already migrated — what they got wrong, what they underestimated, and what they would do differently. Start there if you want to know what the standard path costs in practice.

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