Harvest Now, Decrypt Later: How the Quantum Threat Already Affects Your Data

The answer, up front

Harvest now, decrypt later (HNDL) means an attacker copies encrypted data today and stores it until a quantum computer can decrypt it 1. Data is at risk if it must stay secret longer than a quantum computer takes to arrive plus the time your migration takes. If data must stay secret 10 years or more, treat it as exposed.

What HNDL is

The Canadian Cyber Centre defines an HNDL threat as a threat actor intercepting encrypted information, storing it, and decrypting it later when sufficiently powerful quantum computers exist 2. The June 2026 executive order describes the same risk and uses it to justify accelerated federal migration 1.

The attacker needs no quantum computer today. Recording traffic on a network path costs far less than building a machine that can break RSA. The quantum computer is the only missing piece.

Why HNDL changes the deadline

Most organizations ask, "When will a quantum computer arrive?" That question hides the more useful one: "How long must this data stay secret?"

The Global Risk Institute frames the planning problem with three variables: data shelf life, migration time, and the quantum threat timeline 3. The report names the combined test the Mosca inequality, after Michele Mosca's 2013 work 3. In plain terms:

If shelf life + migration time is greater than time until a quantum computer arrives, your data is already at risk.

You control the first two numbers. You do not control the third, which is why you cannot wait for it.

The 10-year test

The 10-year threshold is ArcQubit's rule of thumb, not a figure from a standard or a regulator. We use it because it is easy to apply and errs on the side of caution. Your own shelf-life, migration and threat estimates may move the line, so treat the test as a triage tool and not a verdict.

Ask this about each data set:

Does this data need to stay secret for 10 years or more?

• Yes: Treat it as exposed. Prioritize it for migration now.
• No, but it needs 5 to 10 years: Put it in your second wave and confirm your migration timeline fits.
• No, under 5 years: Standard planning applies.

Then run three follow-up checks:

1. Does anyone see this data in transit over a public network? The Cyber Centre tells departments to treat systems that protect confidentiality in transit over public network zones as high priority because of HNDL 2.
2. Will the data still be sensitive in 2030? OMB tells agencies to prioritize systems that hold data expected to remain mission-sensitive in 2030 4.
3. Do you know where the data travels and which algorithms protect it? If not, you need an inventory first. Cryptographic Inventory and CBOM Guide covers how to build one.

Which data usually fails the test

Look first at:

• Health and genomic records
• Financial account records and long-term contracts
• Intellectual property and trade secrets
• Government and defense communications
• Identity and credential data that people reuse for years

The Cyber Centre's guidance names information lifespan and the impact of compromise as prioritization factors 2.

HNDL threatens confidentiality, not authentication

HNDL applies to encrypted data captured in transit or at rest. A stolen signature has no future value if the attacker cannot forge new ones today. That is why both the U.S. order and Cloudflare split the work in two phases: key establishment first, then signatures and authentication 1, 5. The executive order sets Dec. 31, 2030, for key establishment and Dec. 31, 2031, for digital signatures 1.

Cloudflare reports that post-quantum encryption, which it enabled for all websites and APIs in 2022, mitigates HNDL for that traffic, while it targets full post-quantum authentication by 2029 5. On Sep. 29, 2026, Cloudflare reported that about 70% of browser-generated traffic reaching its network used hybrid ML-KEM key exchange 6.

What to do about HNDL this quarter

1. Rank your data by shelf life. Use the 10-year test.
2. Find the links that carry long-lived data. Start with public-network paths: VPNs, TLS endpoints, APIs, and partner connections.
3. Turn on hybrid key exchange where you can. Hybrid vs. Pure Post-Quantum explains the hybrid approach.
4. Ask vendors and cloud providers for dates. The Cyber Centre also advises building PQC into procurement clauses 2.
5. Record what you find in a cryptographic bill of materials. Cryptographic Inventory and CBOM Guide shows the fields.

What this means for executives and the board

HNDL turns a technical topic into a governance topic. The attack has a quiet start. Nobody notices a copy of encrypted traffic, and nobody sends a ransom note. The harm arrives years later, after the window to fix the problem has closed.

That timing shapes who owns what. Your CISO owns the technical plan. Your CEO and board own the question of how long the organization promises to keep certain information secret. Your general counsel owns the contracts and regulatory duties that set those promises. Your CFO owns the budget that a multi-year migration needs. No single executive can answer the shelf-life question alone.

Frame the risk in business terms, not cryptographic ones:

• The exposure is a stock, not a flow. Data already captured cannot be recalled. Every month of delay adds to the pile that a future attacker could read. ArcQubit guidance: treat this as a one-way risk.
• Nobody can confirm who is collecting what. No public source confirms which data sets adversaries have gathered. The U.S. executive order still treats HNDL as a reason to accelerate migration 1. Plan around the risk and do not wait for proof.
• The fix is mostly key exchange. NIST says current applications can keep using AES with 128, 192 or 256-bit keys 7. The exposed part is the public-key exchange that sets up a session 4. That narrows the scope, which helps your budget conversation.

What it costs to wait

We do not put numbers on this, because every organization differs. We do name the costs, and you can rank them for your own business.

• Data you already sent stays sent. Traffic that crossed a public network with classical key exchange is outside your control today. Switching later protects future traffic, not past traffic.
• Procurement takes time. Your vendors and cloud providers must ship post-quantum support before you can turn it on. The Cyber Centre advises building PQC into procurement clauses 2. Contracts you sign this year set what you can demand next year.
• Supplier dependence limits your speed. Your migration can move only as fast as your slowest critical supplier. Cloudflare, for example, reports that about 70% of browser-generated traffic reaching its network used hybrid ML-KEM key exchange 6. Your own partners may sit far behind that figure. Ask them.
• Audit and regulatory exposure grows. The executive order sets Dec. 31, 2030, for key establishment 1. OMB tells agencies to prioritize long-lived sensitive data 4. Regulators and customers who follow federal guidance may ask you the same questions. A vague answer costs credibility.
• You cannot prioritize what you have not found. An inventory takes time to build. Every quarter without one delays every other step.

Questions to ask your team this week

Put these to your CISO, CIO and heads of data and legal. Expect written answers, not verbal reassurance.

1. Which data sets must stay secret for 10 years or more, and who owns each one?
2. Which of those data sets cross a public network, and over which links (VPNs, TLS endpoints, APIs, partner connections)?
3. Which data will still be sensitive in 2030 4?
4. Do we know which algorithms protect each of those links? If not, when will the inventory be done?
5. Where do we already use hybrid key exchange, and where can we turn it on next?
6. Which vendors and cloud providers have given us dates for post-quantum support, and which have not?
7. Do our contracts and renewals include post-quantum language 2?
8. Who signs off on the shelf-life assumptions, and when did that person last review them?

Decisions leadership must make in the next 90 days

ArcQubit guidance: keep the first quarter small and concrete.

1. Name one accountable owner. Pick a single executive for HNDL exposure. Give that person authority across security, legal and procurement.
2. Approve the shelf-life ranking. Your data owners propose, your CISO challenges, and your board sees the result. Use the 10-year rule of thumb as a starting point and adjust it with evidence.
3. Fund the inventory. You cannot rank links you cannot see. Approve the time and tools to find them.
4. Set a vendor-dates rule. Require every critical supplier to state its post-quantum plan in writing before its next renewal.
5. Pick a first wave. Choose the long-lived data on public-network paths and start there.

A worked example

Consider a generic mid-sized organization that stores long-term client contracts and keeps a research archive. It runs a site-to-site VPN to a partner, a public API for customers, and a cloud storage service.

The team runs the 10-year test on each data set. The contracts must stay confidential for well over 10 years, so they fail the test. The research archive needs 5 to 10 years, so it lands in the second wave. Routine marketing files need under 5 years, so standard planning applies.

Next, the team asks where the contract data travels. It finds two paths over public networks: the partner VPN and the customer API. Those become the first wave. The team also finds that nobody can say which algorithms protect the VPN, so it adds an inventory task.

Then the CISO asks the VPN vendor and the cloud provider for post-quantum dates. The API sits behind a provider that already supports hybrid key exchange, so the team turns it on. The VPN vendor gives no date, so the general counsel adds post-quantum language to the renewal terms. The team records every finding in a cryptographic bill of materials and reports the ranking, the gaps and the owners to the board.

None of these steps needs a quantum computer, a new standard or a large budget. They need a decision to start.

Common mistakes and how to avoid them

• Waiting for a quantum computer date. You control shelf life and migration time. You do not control arrival. Plan with the first two.
• Treating all encryption as broken. AES remains in NIST's guidance 7. Focus on the key exchange and the public-key layer.
• Confusing HNDL with signature risk. A stolen signature has no future value if the attacker cannot forge new ones today. Sequence key establishment first, then signatures 1, 5.
• Skipping the inventory. Without it, your ranking is a guess.
• Leaving it to the security team alone. Shelf life is a business call. Your data owners and legal team must weigh in.
• Claiming certainty about attackers. Do not tell your board that a named adversary holds your data. No public source supports that claim. Say that the risk is real and the plan is sound.

How to brief your board

Use these talking points, and adapt them to your context.

1. "Attackers can copy encrypted data now and read it once quantum computers can break today's key exchange 1."
2. "Our exposure depends on how long each data set must stay secret plus how long our migration takes."
3. "We have ranked our data by shelf life and named an owner for each first-wave item."
4. "Federal deadlines give a useful benchmark: key establishment by Dec. 31, 2030, and signatures by Dec. 31, 2031 1."
5. "We need your support for the inventory, supplier dates and a quarterly progress report."

How ArcQubit approaches it

ArcQubit's QuCode runs read-only scans and can also ingest the output of scanners you already use. It produces a ranked Quantum Exposure Report with an owner for each finding, sold directly as a fixed-scope discovery. QuTrust then keeps a living migration roadmap and the evidence that shows your board and auditors what changed.