The Quantum Threat.
By Devyansh Lilaramani
Introduction
For over two decades, global digital infrastructure has relied on cryptographic systems such as RSA, elliptic curve cryptography (ECC), and AES, all built on the assumption that the mathematical problems underlying them are computationally infeasible to solve. The emergence of quantum computing challenges this foundation directly. With the development of algorithms such as Shor’s and Grover’s, the security guarantees that protect financial systems, communication networks, government databases, and critical infrastructure now face a measurable and time-bound risk.
Quantum computing and the erosion of classical assumptions
Shor’s algorithm demonstrated that integer factorization and discrete logarithm problems, which form the basis of RSA and ECC, can be solved in polynomial time on a sufficiently powerful quantum computer. Present-day machines lack the stability and qubit count required to compromise real-world cryptographic parameters, but experimental demonstrations of small-scale factoring confirm that the underlying method works in principle. Grover’s algorithm reduces the effective security of symmetric systems by providing a quadratic speedup for brute force key search. This does not break algorithms like AES outright, but it significantly narrows their safety margins.
A present threat created by long-term data value
The most immediate risk does not come from a future quantum computer that can break RSA in a single day. It comes from a strategic behaviour that is already occurring. This behaviour is often described as the harvest now, decrypt later model. Encrypted data intercepted today can be stored indefinitely. Once quantum hardware matures, this archived data may become readable, regardless of how secure it appeared when it was collected. Communications with long-term value, including diplomatic, medical, financial, and corporate records, are therefore vulnerable even if quantum computers remain limited in the near term.
Post-quantum cryptography as a structural response
Mitigating these risks requires replacing vulnerable public key systems rather than attempting to reinforce them. Post-quantum cryptography provides a family of mathematical constructions that remain secure against both classical and quantum attacks while still being deployable on existing hardware.
Several approaches have emerged as leading candidates:
Lattice-based systems.
Schemes such as CRYSTALS Kyber, standardized as ML KEM, and CRYSTALS Dilithium rely on the hardness of problems such as Learning With Errors. These systems provide strong security and practical performance, making them suitable replacements for RSA and ECC. They also offer relatively small key sizes and efficient operations, which allows them to integrate into existing communication protocols with minimal disruption.
Hash-based signatures.
SPHINCS Plus, standardized as SLH DSA, derives its security from cryptographic hash functions rather than number theoretic assumptions. This results in conservative and long term signature security that is less sensitive to unforeseen mathematical breakthroughs. Although signature sizes are larger than those of classical systems, their predictable behaviour and lack of hidden structure make them attractive for high assurance environments.
Code-based cryptography.
Systems such as Classic McEliece and the newly selected HQC rely on the difficulty of decoding general error correcting codes without structural information. They are robust and well studied, although some require large public keys. Their long history of surviving extensive cryptanalytic efforts provides additional confidence that they will remain secure even as quantum hardware progresses.
Multivariate schemes.
These systems rely on the difficulty of solving systems of quadratic equations over finite fields. Several candidates initially appeared promising, but work such as the successful attack on Rainbow demonstrated significant weaknesses. Continued research may yield more resilient variants, but the field currently demands caution until additional schemes demonstrate stronger resistance to real-world attacks.
The NIST standardization effort has created a clear pathway for global adoption by selecting algorithms that balance security requirements with performance and implementability.
The scale of the migration challenge
The transition to post-quantum systems presents a far more complex challenge than simply replacing one algorithm with another. Cryptographic protocols are deeply embedded within operating systems, industrial control systems, embedded devices, browsers, payment networks, and global communication infrastructure. Many devices cannot be updated easily. Others rely on long life hardware cycles that delay coordinated upgrades.
Effective migration will require cooperation between governments, standards organizations, software vendors, hardware manufacturers, and service providers. Without this coordination, even mathematically secure post quantum algorithms may not deliver the level of protection required.
Conclusion
Quantum computing does not yet possess the capability to break modern cryptographic standards, but its trajectory makes the long term reliability of classical systems increasingly uncertain. The demonstrated feasibility of quantum attacks, combined with ongoing hardware improvements and the persistence of stored encrypted data, introduces a clear and urgent need to transition toward quantum resistant standards.
Post quantum cryptography provides a viable foundation for future security. Its success, however, will depend on timely global migration and careful implementation. The stability of digital trust, spanning government systems, financial infrastructure and personal privacy, now rests on how quickly and effectively this transition is executed.
