The Next Wave of Cyber Threats
Cybersecurity has always evolved alongside technology, but quantum computing represents a once-in-a-generation disruption.
Unlike incremental changes such as cloud migration or AI adoption, quantum computing introduces a fundamental shift in computational power that would let attackers break the public-key cryptography securing the digital world today.
No quantum computer can do this yet, but the risk to data is no longer theoretical.
Technology companies, national laboratories and start-ups around the world are racing to build large-scale, fault-tolerant quantum computers. Among the problems such machines could solve are the very equations that keep your encrypted data safe.
The Quantum Threat to Encryption
The most common public-key systems used today, such as RSA, Diffie-Hellman and elliptic-curve cryptography (ECC), depend on mathematical problems like factoring large integers (the product of two large primes) or solving discrete logarithms.
A large enough quantum computer running Shor’s algorithm could solve these problems efficiently, breaking this traditional public-key cryptography. Symmetric encryption such as AES-256 is far less exposed and remains considered secure.
This means that, if a cryptographically relevant quantum computer (CRQC) emerges:
- Recorded TLS sessions (used in HTTPS) that relied on RSA or (EC)DH key exchange could be decrypted.
- Digital signatures could be forged, undermining certificates and software updates.
- Long-term encrypted data archives and communications could be fully exposed.
This potential future event is often called Q-Day: the moment quantum computers can break today’s public-key encryption standards.
How Close Is Q-Day?
Nobody knows the date, but the evidence points to the next decade rather than the distant future:
- Expert opinion: in the Global Risk Institute’s Quantum Threat Timeline Report 2025 (Michele Mosca and Marco Piani, published 9 March 2026), the 26 experts surveyed judged a CRQC “quite possible” (28–49%) within the next 10 years and “likely” (51–70%) within 15 years.
- Falling resource estimates for RSA: in May 2025, Google’s Craig Gidney estimated that RSA-2048 could be factored in under a week with fewer than one million noisy qubits, down from about 20 million in his 2019 estimate with Martin Ekerå. The estimate assumes a 0.1% gate error rate.
- Falling estimates for ECC: in March 2026, Google Quantum AI estimated that 256-bit elliptic-curve keys could be broken with fewer than 1,200 logical qubits (or 1,450 for a faster variant), or fewer than 500,000 physical qubits on a superconducting machine, in a matter of minutes.
Today’s largest machines are still far from these requirements, but the gap is narrowing from both directions.
What Is “Harvest Now, Decrypt Later” (HNDL)?
Even before quantum computers reach full strength, attackers can exploit the time gap. By collecting encrypted data today (medical records, financial transactions, military communications and intellectual property), they can decrypt it in the future once quantum capabilities mature.
This approach is known as “Harvest Now, Decrypt Later” (HNDL). NIST describes it in IR 8547 (October 2026) as a threat “in which adversaries collect encrypted data now with the goal of decrypting it once quantum technology matures”, and calls it one of the main reasons the transition is urgent.
The threat does not wait for Q-Day: data harvested today is already at risk.
Why This Matters
- Sensitive data often has long confidentiality lifetimes: years or even decades.
- Compromised data could lead to national security risks, regulatory breaches or loss of trust years after it was collected.
- Many organisations are unaware that their current encryption lifecycle exposes them to this risk.
In other words:
Even if quantum decryption is not here yet, the quantum threat timeline has already started.
How Harvest Now, Decrypt Later Works
- Interception or Access: attackers intercept encrypted network traffic or exfiltrate encrypted data.
- Storage: they keep this encrypted data in large-scale storage.
- Wait: they wait until quantum computing or new cryptanalysis methods allow decryption.
- Decryption: once capable, they decrypt the data, gaining access to years of harvested confidential information.
This type of attack is hard to spot because nothing at the time of collection reveals that decryption will follow: it looks like ordinary interception or exfiltration. By the time decryption becomes possible, it is too late to revoke or rotate keys; the data is already exposed. Signatures are different: they cannot be harvested in advance, but once a CRQC exists they could be forged, so signature migration matters before Q-Day too.
Organisations at Risk
Organisations dealing with long-lived data and high-value intellectual property face higher exposure. The lifetimes below are indicative, based on how long such data typically stays sensitive; set your own values from your data classification and retention obligations:
|
Organisation Type
|
Data Type
|
Indicative Confidentiality Lifetime
|
|---|---|---|
|
Banking, Finance, Insurance
|
Transaction records, customer data, compliance data
|
30+ years
|
|
Healthcare
|
Patient data, research results, genomics
|
20+ years
|
|
Government, Defence
|
Classified intelligence, diplomatic cables, PII
|
50+ years
|
|
Telecom & Communications
|
Encrypted communications, PII, IoT
|
Continuous
|
|
Critical Infrastructure, Utilities
|
Critical infrastructure data, Cyber Physical Systems Data (OT, IoT)
|
Michele Mosca’s widely used rule of thumb: if the number of years your data must stay secret, plus the years it will take you to migrate, is greater than the years until a CRQC arrives, you are already exposed. With migrations commonly taking many years, even data that must stay confidential for five years or so can be at risk today.
Organisations that begin crypto-agility and PQC migration now will be prepared before the quantum threat becomes operational.
Responding to the Threat: Quantum Readiness Starts Now
Regulators have set the pace. NIST IR 8547, Transition to Post-Quantum Cryptography Standards (final, 27 October 2026), deprecates quantum-vulnerable public-key algorithms after 2030 and disallows them under NIST standards after 2035. The UK NCSC (20 March 2025) asks organisations to complete discovery and an initial plan by 2028, priority migrations by 2031 and full migration by 2035. US OMB Memorandum M-26-15 (24 June 2026) requires federal high value assets and high impact systems to use PQC for key establishment by 31 December 2030 and for signatures by 31 December 2031. The EU’s Coordinated Implementation Roadmap (v1.1, June 2025) asks Member States to take first steps by the end of 2026 and protect high-risk use cases by the end of 2030.
A Post-Quantum Cyber Readiness roadmap should include the following actions:
Start Crypto Discovery Now: map where and how encryption is used, including certificates, APIs, applications and endpoints. An Enterprise Cryptographic Exposure Management platform such as Quantum Sentinel supports PQC discovery, cryptographic inventory (CBOM), exposure assessment and migration planning using read-only metadata collection.
Classify Data by Longevity: identify data that needs long-term protection. These are your most quantum-exposed assets and the first candidates for migration.
Deploy Crypto Agility Frameworks: build systems that can switch from RSA/ECC to quantum-safe algorithms without major re-engineering.
Adopt PQC Pilots: test NIST’s final standards (ML-KEM, ML-DSA, SLH-DSA), starting with hybrid ML-KEM key exchange in TLS 1.3, which counters HNDL directly.
Integrate Quantum Readiness into Policy: embed quantum-risk assessments into enterprise governance, vendor contracts and data-protection strategies.
Educate Leadership: ensure that board members and executives understand that quantum risk means long-term data exposure, not just a technical issue.
The Invisible Breach Has Already Begun
Quantum threats are not only about tomorrow’s technology; they are about today’s inaction.
Every encrypted dataset harvested today could become tomorrow’s breach headline.
The shift to Post-Quantum Cryptography is one of the most important cybersecurity transformations of our time.
Preparing for it now means protecting not just your systems, but your organisation’s future.
Organisations that act now will:
Meet regulator and customer expectations as PQC deadlines arrive.
Protect customer trust and brand reputation.
Gain a competitive edge as quantum-ready pioneers.
Sources: Global Risk Institute, Quantum Threat Timeline Report 2025 (9 March 2026); C. Gidney, arXiv:2505.15917 (May 2025); Google Quantum AI, Safeguarding cryptocurrency by disclosing quantum vulnerabilities responsibly (31 March 2026); NIST IR 8547, final (27 October 2026); UK NCSC, Timelines for migration to post-quantum cryptography (20 March 2025); US OMB M-26-15 (24 June 2026); EU NIS Cooperation Group, Coordinated Implementation Roadmap for the Transition to Post-Quantum Cryptography v1.1 (23 June 2025).
Our Post-Quantum Readiness Series
This article is Part 2 of our Post-Quantum Cyber Readiness Series, which explains complex quantum-security concepts in practical terms.
The series covers:
For a current view of deadlines and regulator expectations, see also PQC Migration Readiness in 2026.
Each article is written to help CEOs, CISOs, IT leaders and architects navigate the quantum transition with confidence.
