Quantum computing has the potential to transform scientific research, financial modelling, logistics and data analysis. At the same time, it creates a major cybersecurity challenge. Many cryptographic algorithms used to protect digital communications, identities and sensitive information were not designed to withstand attacks from large-scale quantum computers.

A cryptographically relevant quantum computer is not available today, and its arrival cannot be predicted with certainty. However, waiting for that moment would leave organizations with little time to identify vulnerable systems and replace deeply embedded cryptography. NIST has already encouraged organizations to begin transitioning to finalized post-quantum cryptography standards. For security professionals, quantum security is therefore becoming a present-day risk management and resilience priority, requiring them to focus on combating emerging quantum threats.

Key Emerging Quantum Threats  

1. Public-Key Cryptography Could Become Vulnerable

The most widely discussed quantum threat is the potential compromise of public-key cryptography. Algorithms such as RSA and elliptic-curve cryptography are used for secure web connections, virtual private networks, certificates, email security, digital identities and key exchange.

These algorithms rely on mathematical problems that are extremely difficult for classical computers to solve. A sufficiently powerful quantum computer running Shor’s algorithm could solve some of these problems much faster, weakening the security foundations of many digital systems.

2. Harvest Now, Decrypt Later Attacks

“Harvest now, decrypt later” is one of the most immediate quantum security risks. Attackers can collect encrypted information today and retain it until future quantum systems are capable of decrypting it.

This threat is particularly relevant to information that must remain confidential for many years, including payment data, financial records, intellectual property, government information, healthcare records and strategic business communications.

A structured quantum risk assessment can help organizations identify high-priority data assets and cryptographic dependencies.

3. Digital Signatures and Identity Systems May Be Undermined

Quantum threats extend beyond encryption. Public-key cryptography also supports digital signatures that verify software, transactions, documents, users and devices.

If attackers can compromise these signature mechanisms, they may be able to impersonate trusted entities, forge certificates, sign malicious software or manipulate digitally approved records. The result could be a breakdown of trust across public key infrastructure, software supply chains, cloud services and machine-to-machine communication.

4. Symmetric Encryption May Lose Part of Its Security Margin

Symmetric encryption algorithms such as AES are generally more resistant to quantum attacks than public-key cryptography. However, they are not completely unaffected.

Grover’s algorithm could theoretically accelerate the search for encryption keys, reducing the effective security margin of some symmetric configurations. Stronger key sizes can help address this concern, but organizations must also evaluate implementation quality, key management, rotation practices and the sensitivity of the protected information.

5. Hidden Cryptography Can Delay Migration

Most organizations do not have a complete view of where cryptography is used. Algorithms, certificates and keys may be embedded across applications, APIs, databases, cloud platforms, hardware security modules, backups, connected devices and third-party products.

These hidden dependencies can make post-quantum migration complex and disruptive. A vulnerable algorithm may be deeply embedded in a critical application or supported by a vendor that has not yet developed an upgrade path.

6. Poorly Planned PQC Migration Can Create New Risks

Moving to post-quantum cryptography is not a simple software update. Post-quantum algorithms may have different key sizes, signature sizes, performance requirements and compatibility limitations.

A rushed implementation could introduce outages, latency, interoperability problems or security gaps. Organizations may also need to operate hybrid environments that support classical and post-quantum algorithms during the transition.

7. Third-Party Systems Can Extend Quantum Exposure

An organization may modernize its internal cryptography while remaining exposed through cloud providers, software vendors, payment partners, APIs and other connected services.

Third-party products may rely on vulnerable algorithms or have long upgrade cycles. Procurement and vendor risk programs should therefore assess each supplier’s post-quantum roadmap, algorithm support, certificate practices and ability to deliver cryptographic updates.

Building Practical Quantum Security Capabilities

Preparing for quantum threats requires more than awareness.  

The first step towards quantum security readiness is to establish cryptographic visibility. Security teams should build an inventory of algorithms, certificates, keys, libraries, protocols and business systems, then prioritize them according to exposure and business impact.

SISA Institute’s Certified Quantum Security Professional (CQSP) program helps security professionals build practical capabilities across quantum-safe cryptography, quantum risk assessment, post-quantum migration and alignment with standards from NIST, ISO and ETSI. The program combines theoretical foundations with hands-on labs and real-world scenarios to help professionals move from understanding quantum threats to planning an effective response.

The timeline for cryptographically relevant quantum computing remains uncertain, but the actions required are already clear. By improving cryptographic visibility, protecting long-lived data, strengthening cryptographic agility and building internal expertise, organizations can move from quantum awareness to measurable readiness.

‍