Quantum Security 101
Quantum computers will eventually break the public-key cryptography that protects enterprise data in transit and at rest. Understand what that means, why the clock has already started, and what to do now.
The Threat
The same break in public-key cryptography undermines both the confidentiality of stored data and the integrity of digital signatures.
One exposes what you kept secret. The other lets an attacker forge what others trust.
Adversaries intercept and store encrypted data today, waiting to decrypt it when a sufficiently powerful quantum computer arrives.
A stolen encrypted file can be read the moment that computer succeeds. The exposure is retroactive and cannot be undone after the fact.
The public-key cryptography behind digital signatures and certificates can also be broken by a quantum computer.
An attacker could forge signatures at internet scale: impersonating trusted vendors, signing malicious firmware, issuing fraudulent certificates, and backdating transactions.
One layer down, the mechanism is Shor’s algorithm (1994), which breaks both RSA and elliptic-curve cryptography. Elliptic-curve signatures, used across PKI and code-signing, are expected to fall sooner than RSA encryption because they require far fewer quantum operations.
Q-Day Timeline
Q-Day is the point at which a cryptographically relevant quantum computer can break RSA and elliptic-curve cryptography, the mathematics underpinning almost all internet security today.
The Global Risk Institute’s Quantum Threat Timeline Report, which surveys more than 30 global experts, places the most likely window in the 2030s, with conservative forecasts reaching into the 2040s.
Announced by Google’s security engineering leadership in March 2026, a full year ahead of the NIST deprecation target of 2035.
Planning Horizons
The Math
In 2015, cryptographer Michele Mosca formalized quantum risk into a single inequality that every board should understand.
Your total protection time (A + B)
Threat arrival time (C)
If A + B > C, your organization is already vulnerable.
Most enterprises need years to migrate cryptography completely, and large, complex estates can need well over a decade. If your data must stay confidential beyond 2030, the time to start is now.
3–5 yr
Small enterprise
8–12 yr
Mid-market
12 yr+
Large or complex estate
Regulatory Landscape
Quantum-safe migration is a compliance obligation, not only a security upgrade. Standards bodies and regulators across major markets have finalized algorithms or set dated migration targets.
Industry Exposure
Exposure is not uniform. Sectors that combine long data-confidentiality lifetimes with heavy regulation are first in line, and for many of them quantum readiness is already an audited or contractual requirement.
01
Transaction and customer records carry decade-plus retention. DORA, PCI DSS 4.0, and the EU PQC Roadmap will surface in upcoming audit cycles.
02
Classified communications have the longest secrecy requirements of any sector. CNSA 2.0 mandates quantum-safe acquisitions from January 2027.
03
Patient records carry 7 to 30 year retention. Genomic data is permanently sensitive and cannot be re-encrypted once exposed.
04
Grids, water, satellites, and telecom rely on industrial control systems with multi-decade replacement cycles. The EU PQC Roadmap targets migration by 2030.
05
Devices shipped today will operate for 10 to 20 years. PQC-capable firmware will be required, and non-upgradeable hardware will become unsellable to regulated buyers.
06
Oracle attestations, L2 fraud proofs, cross-chain messages, and smart-contract signatures use ECC. Institutional partners will inherit PQC deadlines.
07
Transport hardware has the longest lifecycles of any commercial sector. Vehicles deployed in 2026 without quantum resistance remain vulnerable for full service life.
08
Identity data persists indefinitely. Credentials issued today on ECC-signed systems remain permanently vulnerable to retroactive forgery.
Recommended Actions
None of these require waiting for a quantum computer to exist. Each is a planning step you can start this quarter.
01
Map where RSA and elliptic-curve algorithms live across TLS, PKI, HSMs, certificates, code-signing, and third-party services.
02
Rank systems by how long their data must stay confidential, measured against the harvest-now window.
03
Make the ability to swap algorithms a procurement and architecture standard for new systems now.
04
Confirm the post-quantum migration plans of your cloud, VPN, and software providers, as Google has urged the industry to do.
05
Commission an independent, human-led snapshot that tells the board where to act first.
Board Meeting Material
The briefing explains the threat without technical overhead, anchors the timeline to current expert data and regulatory mandates, and gives the board five concrete actions they can approve in a single meeting.
It is a decision-support tool for the room where quantum risk either gets funded or ignored.
What to do now
Start with a quantum threat assessment. You cannot migrate what you cannot see.
Horizen Labs runs a human-led cryptographic exposure assessment that requires no software deployment and makes no changes to live systems, producing a board-ready exposure snapshot.
Talk to the Quantum Security teamMore education and awareness
Common questions
Harvest now, decrypt later (HNDL) is an attack in which adversaries store encrypted data today and decrypt it once a capable quantum computer exists. It makes quantum risk present-tense: any data that must stay confidential for years is already exposed.
Both. A code-breaking quantum computer does not exist yet, with most expert forecasts pointing to the 2030s. But because of harvest-now-decrypt-later, and because migration takes years, the risk and the work are present-day.
Quantum-safe migration is already a compliance obligation in several markets. NIST finalized its first quantum-resistant standards (FIPS 203, 204, 205) in August 2024, the EU’s DORA requires cryptographic resilience, and the US NSA’s CNSA 2.0 sets dated targets through the 2030s.
Typically three to five years for a small enterprise, eight to twelve for mid-market, and well over a decade for a large or complex estate. Against regulatory deadlines and the harvest-now window, most programs are already behind.
The same thing. Post-quantum cryptography (PQC) is the research and standards term; quantum-resistant is the plainer, equivalent term Horizen Labs uses. Both describe algorithms designed to withstand a quantum computer.
Start by understanding your exposure before planning a migration. A cryptographic exposure assessment shows where vulnerable algorithms live and tells your board where to act first.
