I have watched capable CISOs hesitate on quantum computing in a way they never would on cloud architecture or a new cryptographic protocol, and the reason is almost always the same: a feeling that this particular subject requires physics they never studied. It doesn't. The perceived barrier is real, but it is higher than the actual conceptual load required. Your job is not to understand quantum mechanics. It is to understand which cryptographic systems are affected by which quantum algorithms and what the organisational response is. That is a bounded, learnable set of facts, not a physics degree.
This article is deliberately narrow. It does not cover how to brief your board, how to build the investment case, or ongoing governance framing; QSECDEF already has dedicated coverage of each of those. This one addresses the step before all three: getting to a working understanding in the first place, without wading through mathematics you do not need.
The barrier feels bigger than it is because of where the unfamiliarity sits, not because of its actual depth. CISOs routinely master genuinely difficult, unfamiliar technical domains as a normal part of the role: cloud architecture, cryptographic protocol design, container security, the internals of a new SIEM platform. None of that is easy, and none of it stops a competent CISO for long. Quantum computing feels different mainly because the vocabulary (superposition, entanglement, qubits) sounds like physics rather than infrastructure. Strip the vocabulary away and what is left is a smaller, more familiar problem: a new class of hardware that changes which cryptographic assumptions still hold, and a fixed set of facts about which ones break and when.
The four facts that matter, and nothing else
Shor's algorithm, published by Peter Shor in 1994, threatens RSA, ECC, and Diffie-Hellman because it solves integer factorisation and the discrete logarithm problem in polynomial time on a sufficiently capable quantum computer. Those are the mathematical problems that make current public-key cryptography hard to break classically. Shor's algorithm removes that hardness. You do not need to follow the proof to use this fact correctly.
Grover's algorithm, published by Lov Grover in 1996, provides only a quadratic speedup against symmetric encryption. This is a materially smaller threat than Shor's, and it is addressed by moving to longer key lengths: AES-256 and hash outputs of SHA-384 or SHA-512 retain adequate margin. AES-128 does not. This is why the migration conversation for symmetric cryptography looks completely different from the migration conversation for RSA and ECC.
The hardware to run Shor's algorithm at cryptographically meaningful key sizes does not exist yet. Estimates for breaking RSA-2048 run to hundreds of millions of physical qubits under current error-correction approaches; today's machines have thousands. That gap is measured in orders of magnitude, not a generation of incremental improvement.
NIST has already standardised the replacement algorithms. FIPS 203 (ML-KEM), FIPS 204 (ML-DSA), and FIPS 205 (SLH-DSA) were finalised in August 2024. You do not need to understand the lattice mathematics behind ML-KEM to know that it is the standardised replacement for RSA and ECC key establishment. That is a fixed migration target, not an open research question, and it is the fact that turns quantum risk from an abstract worry into a planning input.
Read those four back. If you can repeat them accurately to a colleague, you have the core of what this article set out to give you.
The one concept that changes the timeline: HNDL
Harvest Now, Decrypt Later requires no physics at all, and it is the single addition to your mental model that matters most beyond the four facts above. Encrypted data captured today can be stored and decrypted later, once capable hardware exists. That means the migration window is already open for any data with a long confidentiality requirement, regardless of when a cryptographically relevant quantum computer actually arrives. The risk is not a future event on a calendar. It is a present exposure for specific categories of data your organisation is generating right now.
Once you understand HNDL, the natural next step is assessing your own exposure. QSECDEF's post-quantum risk assessment tool walks through that assessment without requiring a cryptographic background to use it.
Put HNDL in terms of your own data, not an abstract adversary. Financial models with a multi-year confidentiality requirement, clinical trial data, source code for a product still years from release, communications under legal privilege: any of these encrypted today with RSA or ECC key exchange is potentially exposed the day a cryptographically relevant quantum computer arrives, regardless of when that day actually falls on a calendar. The migration decision is not "wait until the threat is closer." For data with a long confidentiality window, the threat is already accumulating in whatever an adversary has already captured and stored.
Sessions 1, 2, and 4 of the QSECDEF Summer Bootcamp cover this material in full, with no prior background required.
Where a CISO goes from here
With the four facts and HNDL in hand, the next steps are ones QSECDEF has already written up in detail, and there is no point repeating them here. For how to communicate this upward, our guide to briefing your board covers structuring a briefing that produces a decision rather than just awareness. For building the investment case once the risk is understood, the CISO's case for quantum security investment gives you the financial exposure proxies and the specific ask to bring to a CFO. For the fuller technical picture behind the four facts above, our overview of quantum computing and cybersecurity goes deeper without assuming a physics background either.
Delegating the mathematics to your technical team is correct. Delegating the governance judgement, the timing decision, the board communication, is not; that stays with you, informed by technical staff rather than replaced by them. This distinction matters in practice more than it sounds like it should. A cryptographic architect can tell you precisely how many systems still depend on RSA-2048 and how long each migration workstream will take. What a cryptographic architect cannot decide on your behalf is whether the organisation starts that migration this budget cycle or the next one, how it gets sequenced against every other security priority competing for the same engineering time, or how the risk gets framed for a board that has never heard of ML-KEM. Those are governance calls, and the four facts and HNDL concept above are what let you make them from a position of actual understanding rather than deference to whoever in the room sounds most confident.
None of this requires you to become the technical expert in the room. It requires you to be able to ask the right question of the technical expert in the room, and to recognise a genuinely well-reasoned answer when you get one. That is a lower bar than "understand quantum mechanics," and it is the bar this article was written to clear.
If you want to extend this same access-barrier removal beyond yourself to the wider team who will actually execute a migration, upskilling your team without hiring a physicist is the article to read next.
