The program
Prioritizing when everything cannot move at once
A migration budget is finite and the inventory is long — prioritize by data lifetime, exposure, and harvestability, not by algorithm counts.
5 min read
What you'll be able to do
- Prioritize systems and data using data lifetime, exposure, and harvestability rather than counting weak algorithms.
- Explain crypto agility as a durable capability rather than a one-time project.
- Recognize why a fixed list of algorithms today does not mean the list is finished.
An inventory tells you what exists. It does not tell you what to do first. With a finite budget and a long list, prioritization is the decision that determines whether the program delivers risk reduction in year one or spends a year moving low-risk systems simply because they were easy.
- How long the data behind a system must stay confidential — the X in the Mosca heuristic from the previous module.
- Whether traffic is exposed to passive collection at all. Internet-facing beats partner-facing beats internal-only; a system that cannot be harvested is not urgent no matter how weak its cryptography looks on paper.
- How reachable and exploitable the system is today, independent of the quantum question. A system with other open problems should not wait for a post-quantum-only conversation.
- How confident you actually are in the evidence. A finding from an automated scan and a finding confirmed by a person carry different weight in a prioritization meeting.
A one-time swap is not the goal, because the list of algorithms is not finished. HQC was only selected as a backup key-establishment algorithm in March 2025, and a FALCON-based signature standard is still a draft. An architecture that can swap a cryptographic primitive without a redesign, called crypto agility, survives that kind of change. An architecture that hard-codes today's choice repeats this entire project the next time a primitive is deprecated.
| If your team says | What it usually means |
|---|---|
| We are fully post-quantum now | Worth asking whether that claim covers authentication as well as key exchange — most organizations are hybrid on the latter and still classical on the former |
| We picked one library and moved on | A one-time swap, not agility — ask what happens when the next algorithm is deprecated |
| We prioritized by counting flagged algorithms | A count, not a risk ranking — ask about data lifetime and exposure next |
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