Every day, organisations rely on encryption to protect online banking, healthcare records, corporate communications, cloud infrastructure, and digital identities.
Much of today's public-key cryptography relies on mathematical problems that are extremely difficult for conventional computers to solve. RSA and elliptic-curve cryptography, for example, underpin important parts of secure communication and digital authentication.
Quantum computing introduces a potential challenge to these systems. A sufficiently powerful, fault-tolerant quantum computer could use specialised quantum algorithms to break widely deployed public-key cryptographic schemes.
Such a machine is not currently available at the scale required to break modern cryptography in practice. However, organisations cannot safely assume that their sensitive data will remain protected indefinitely.
An attacker could collect encrypted information today and retain it until future technology makes decryption feasible. This strategy is known as harvest now, decrypt later.
The response is post-quantum cryptography (PQC): cryptographic algorithms designed to resist attacks from both classical and quantum computers.
The challenge for security teams is to identify vulnerable cryptographic systems, plan a controlled migration, and protect sensitive information before quantum computing capabilities advance further. <Cite refs={["turn855884search0","turn855884search2"]}/>
Quantum computers process information using quantum bits, or qubits. Unlike conventional bits, qubits can exhibit quantum properties that enable certain algorithms to solve specific problems differently from classical computers.
The security concern is not that quantum computers make every encryption algorithm ineffective. Their impact depends on the mathematical foundations of the cryptographic system.
RSA security relies on the difficulty of factoring sufficiently large integers using known classical methods.
A sufficiently capable quantum computer running Shor's algorithm could efficiently factor those integers, undermining RSA's security assumptions.
Elliptic-curve cryptography (ECC) is used for key agreement and digital signatures. Its security relies on the difficulty of solving certain discrete logarithm problems.
Shor's algorithm also threatens these mathematical foundations, meaning widely used elliptic-curve schemes would require replacement with quantum-resistant alternatives.
Symmetric algorithms, such as AES, are affected differently.
Grover's algorithm can theoretically reduce the search effort for certain brute-force problems, but it does not break symmetric cryptography in the same way Shor's algorithm threatens RSA and ECC.
Appropriate key sizes and sound implementation remain important. Quantum risk therefore requires an algorithm-by-algorithm assessment rather than abandoning all existing cryptography.
One of the strongest reasons to prepare for post-quantum cryptography before a cryptographically relevant quantum computer exists is the possibility of retrospective decryption.
Imagine a financial institution transmitting sensitive records over an encrypted connection. An attacker who obtains a copy of the encrypted traffic may be unable to decrypt it today.
If the attacker retains the data and a future quantum computer can break the public-key mechanisms protecting the relevant session keys, some of that previously captured information could become readable.
The exact exposure depends on the protocol, cryptographic implementation, and how session keys were established. Modern forward-secret key exchange can limit some risks, but quantum-vulnerable key establishment remains a concern.
Information particularly worth protecting includes:
Government and defence communications.
Healthcare and genetic information.
Long-term financial and commercial records.
Intellectual property and research data.
Credentials, secrets, and authentication material.
Sensitive information exchanged with third parties.
The key question is not only how long it may take to build a capable quantum computer. It is how long the information must remain confidential.
If information must remain secret for decades, delaying migration could create a risk that persists long after the original communication occurred. <Cite refs={["turn855884search0","turn855884search25"]}/>
Post-quantum cryptography uses mathematical approaches designed to remain secure against known attacks from both classical computers and sufficiently capable quantum computers.
Unlike quantum key distribution, PQC does not require a quantum communication channel or a quantum computer. Its algorithms can be implemented on conventional computing hardware, subject to compatibility and performance considerations.
In August 2024, the US National Institute of Standards and Technology (NIST) finalised three major post-quantum cryptography standards. Organisations can use these standards as the basis for migration planning. <Cite refs={["turn855884search5","turn855884search1"]}/>
<box gap={3}> <row align="start" gap={3}> <box background="surface-secondary" radius="lg" size="64px" align="center" justify="center"> <icon name="key-round" size="2xl" /> </box> <box flex="1" gap={1}> **ML-KEM — FIPS 203**
<text color="secondary" size="sm">Module-Lattice-Based Key-Encapsulation Mechanism</text> ML-KEM establishes a shared secret between communicating parties over a public channel. That secret can then be used with symmetric cryptography to protect communications. It is derived from the CRYSTALS-Kyber algorithm. </box></row> <divider color="subtle" /> <row align="start" gap={3}> <box background="surface-secondary" radius="lg" size="64px" align="center" justify="center"> <icon name="file-check" size="2xl" /> </box> <box flex="1" gap={1}> **ML-DSA — FIPS 204**
<text color="secondary" size="sm">Module-Lattice-Based Digital Signature Algorithm</text> ML-DSA provides digital signatures used to verify authenticity and detect unauthorised changes. It is derived from CRYSTALS-Dilithium. </box></row> <divider color="subtle" /> <row align="start" gap={3}> <box background="surface-secondary" radius="lg" size="64px" align="center" justify="center"> <icon name="shield-check" size="2xl" /> </box> <box flex="1" gap={1}> **SLH-DSA — FIPS 205**
<text color="secondary" size="sm">Stateless Hash-Based Digital Signature Algorithm</text> SLH-DSA provides a hash-based digital-signature alternative with different mathematical foundations from lattice-based schemes. It is derived from SPHINCS+. </box></row> </box>
These standards serve different purposes. ML-KEM is for key establishment, while ML-DSA and SLH-DSA provide digital signatures. They are not interchangeable, and migration requires choosing algorithms appropriate to each cryptographic function. <Cite refs={["turn855884search1","turn855884search5"]}/>
Post-quantum migration is broader than updating one encryption library. Public-key cryptography appears throughout enterprise infrastructure, often inside systems that organisations do not directly manage.
Potentially affected areas include:
TLS and VPNs: Key establishment used to protect network communications.
Digital certificates and PKI: Certificates and signature mechanisms used to establish trust.
Code signing: Signatures used to validate software and firmware updates.
SSH and administrative access: Public-key authentication and key exchange.
Cloud services: Cryptographic mechanisms embedded in managed services and APIs.
Databases and backups: Encryption and key-management systems protecting stored information.
IoT and operational technology: Devices that may have limited processing capacity or long replacement cycles.
Identity and authentication systems: Digital signatures and public-key credentials used to verify identities.
A system may use multiple cryptographic algorithms at different layers. Replacing one component does not automatically make the entire system quantum-resistant.
Organisations should therefore discover where cryptography is used, identify the algorithms and dependencies involved, and determine which components can be upgraded or replaced.
A successful migration begins with visibility and prioritisation, not an organisation-wide algorithm replacement performed without testing.
Identify systems, applications, services, devices, protocols, and vendors that depend on public-key cryptography.
Record the algorithms used, key sizes, certificate dependencies, data sensitivity, system owners, vendor support, and upgrade constraints.
Automated cryptographic discovery can help, but it may not identify every embedded or externally managed dependency.
Assess how long information must remain confidential and how damaging future exposure would be.
Prioritise data that could remain valuable for many years, along with critical infrastructure and systems that have long procurement or replacement cycles.
Identify where RSA, elliptic-curve key exchange, elliptic-curve signatures, and other quantum-vulnerable mechanisms are used.
Determine whether the cryptography protects confidentiality, authentication, integrity, or multiple functions.
Ask technology providers about their PQC roadmaps, supported standards, compatibility requirements, deployment timelines, and update mechanisms.
Third-party dependencies are especially important when cryptography is embedded in managed platforms, appliances, firmware, or software libraries.
Define owners, priorities, dependencies, milestones, testing requirements, and funding.
Begin with high-risk systems and components that can be migrated safely. Ensure that cryptographic changes are coordinated across clients, servers, certificates, protocols, and supporting infrastructure.
Post-quantum algorithms can change key sizes, signature sizes, handshake behaviour, bandwidth use, memory requirements, and processing demands.
Test realistic workloads and failure scenarios before deploying new cryptographic configurations to production.
Cryptographic agility is the ability to replace or update cryptographic algorithms and implementations without requiring a complete redesign of the surrounding system.
Use supported libraries, centralised configuration, documented dependencies, and controlled update mechanisms so that future cryptographic changes can be implemented more efficiently.
Verify that quantum-resistant algorithms are actually negotiated or used where intended. Monitor failed handshakes, unsupported clients, certificate issues, performance changes, and unexpected fallback to older algorithms.
A migration should be measured by effective coverage, not merely by the number of products labelled quantum-ready.
These steps align with the preparation and migration guidance published by NIST, CISA, and NSA. <Cite refs={["turn855884search2","turn855884search1"]}/>
Consider an organisation that operates a customer-facing web platform, internal VPN, code-signing infrastructure, and long-term encrypted backups.
A quantum-readiness assessment finds that these systems depend on different public-key mechanisms and are maintained by separate teams.
The organisation could proceed as follows:
SystemKey concernPreparation priorityCustomer-facing TLSQuantum-vulnerable key establishment and protocol compatibilityReview vendor support and test PQC-capable configurationsInternal VPNKey exchange and interoperability across clients and gatewaysValidate supported algorithms and migration dependenciesCode-signing infrastructureLong-term trust in software and firmware signaturesPlan signature migration and protect signing keysLong-term backupsConfidentiality of retained dataAssess data secrecy lifetime and encryption/key-management dependenciesLegacy operational devicesLimited upgrade support and long replacement cyclesIdentify compensating controls and replacement timelinesThe organisation should not assume that every system can be upgraded at the same time. The migration sequence should reflect risk, technical feasibility, and dependencies.
Older systems may rely on cryptographic libraries that no longer receive updates or hardware that cannot support newer algorithms.
Defence: Identify unsupported components early, evaluate isolation or compensating controls, and plan replacements for systems that cannot be upgraded.
Larger keys, certificates, or signatures can affect bandwidth, memory, latency, and storage. Protocols may also fail when one endpoint supports a new algorithm and the other does not.
Defence: Conduct interoperability testing and performance benchmarking under realistic conditions.
Organisations may not control the cryptographic implementation used by a cloud provider, vendor appliance, or managed service.
Defence: Establish vendor requirements, track product support, and include cryptographic readiness in procurement and supplier-risk reviews.
Cryptography may be embedded in applications, firmware, libraries, and protocols without a central inventory.
Defence: Combine automated discovery, architecture reviews, software inventories, and vendor assessments.
An incorrect migration can weaken security, introduce implementation vulnerabilities, or cause services to fall back to older cryptographic mechanisms.
Defence: Use established standards and vetted implementations, validate configuration, test rollback procedures, and monitor negotiated algorithms.
A migration can involve software development, hardware replacement, certificate changes, testing, and staff training.
Defence: Prioritise by risk, align work with existing upgrade cycles, and phase changes to reduce disruption.
“Quantum computers can already break all modern encryption.”
No. A cryptographically relevant quantum computer capable of breaking widely deployed public-key cryptography at practical scale has not been demonstrated. The exact timeline remains uncertain. Preparation is necessary because migration takes time and sensitive data may remain valuable for years. <Cite refs={["turn855884search0","turn855884search9"]}/>
“Post-quantum cryptography requires a quantum computer.”
No. PQC algorithms are designed to run on conventional computing systems while resisting known quantum attacks.
“All encryption must be replaced.”
No. The impact differs by algorithm and use case. Public-key key establishment and digital signatures are major priorities, while symmetric cryptography and hashing require separate assessments.
“Buying a quantum-safe product completes the migration.”
No. The organisation must verify algorithm use, interoperability, certificate dependencies, fallback behaviour, and the security of the complete implementation.
“There is no urgency because the threat is in the future.”
This ignores the possibility of harvest-now-decrypt-later attacks and the time required to upgrade complex infrastructure.
Security and infrastructure teams can begin with a focused readiness programme:
Inventory cryptographic assets and dependencies.
Identify data with long confidentiality requirements.
Prioritise systems using quantum-vulnerable public-key algorithms.
Request migration plans from critical vendors.
Review support for NIST's finalised PQC standards.
Test quantum-resistant implementations in controlled environments.
Establish cryptographic agility and update procedures.
Track migration progress and residual exposure.
For SOC teams, the transition also creates monitoring and governance opportunities. Teams should track changes to cryptographic configurations, certificate infrastructure, key-management systems, and security policies. They should investigate unexpected fallback to legacy algorithms where that behaviour violates approved policy.
The SOC is not responsible for redesigning cryptographic protocols alone, but it can help verify that migration controls are enforced and that configuration changes remain visible.
Post-quantum cryptography is a necessary step in preparing digital infrastructure for future advances in quantum computing.
The main challenge is not simply selecting a new algorithm. It is discovering where vulnerable cryptography is used, prioritising the information and systems most at risk, coordinating changes across complex dependencies, and validating that the new protections work correctly.
NIST's ML-KEM, ML-DSA, and SLH-DSA standards provide a foundation for this transition. Organisations should use them as part of a structured programme that includes cryptographic inventory, vendor engagement, interoperability testing, and long-term cryptographic agility.
The exact arrival date of a cryptographically relevant quantum computer remains uncertain. The time required to prepare complex systems is much less uncertain: it can be substantial.
The best time to prepare is before the technology capable of breaking today's protections becomes practical.
Further Reading
NIST: Post-Quantum Cryptography
NIST: What Is Post-Quantum Cryptography?
NIST: Migration to Post-Quantum Cryptography
CISA, NSA and NIST: Quantum-Readiness Guidance
NIST: Cryptographic Standards and Guidelines
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