Quantum computing introduces a fundamental threat to modern digital security. While classical computers process bits (0 or 1), quantum computers utilise qubits, enabling them to perform calculations through superposition and entanglement.

Two primary algorithms pose specific risks:

• Shor’s Algorithm: Capable of solving integer factorization and discrete logarithm problems exponentially faster than classical machines. This effectively breaks widely used public-key encryption standards like RSA and Elliptic Curve Cryptography (ECC).

• Grover’s Algorithm: Offers a quadratic speed-up for searching unsorted databases, reducing the effective security of symmetric encryption (e.g., AES) and hash functions. This necessitates doubling key sizes (e.g., moving to AES-256) to maintain security.

Harvest Now, Decrypt Later (HNDL)

Although a cryptographically relevant quantum computer (CRQC) may not exist until the 2030–2035 timeframe, the threat is immediate due to Harvest Now, Decrypt Later (HNDL) attacks. Adversaries are currently intercepting and storing encrypted data with the intent to decrypt it once quantum technology matures. Consequently, any data with a long secrecy lifespan—such as government secrets, financial records, or healthcare data—is already at risk.

Post-Quantum Cryptography (PQC) Standards

To counter this, the US National Institute of Standards and Technology (NIST) has standardised Post-Quantum Cryptography (PQC)—algorithms based on mathematical problems (like lattice structures) that remain difficult for both quantum and classical computers.

As of August 2024, NIST finalised three primary standards:

1. ML-KEM (FIPS 203): A lattice-based key encapsulation mechanism derived from CRYSTALS-Kyber. It is the primary standard for general-purpose encryption and key exchange.

2. ML-DSA (FIPS 204): A lattice-based digital signature algorithm derived from CRYSTALS-Dilithium. It balances security and performance for authentication.

3. SLH-DSA (FIPS 205): A stateless hash-based signature scheme derived from SPHINCS+. It serves as a conservative backup relying on different mathematical assumptions.

Additionally, FN-DSA (based on Falcon) and HQC (code-based) are being prepared for future standardisation to provide alternative options.

Implementation Challenges

Migrating to PQC involves significant challenges:

• Performance Overhead: PQC algorithms often require larger key sizes and signatures than classical methods (e.g., ML-DSA signatures are significantly larger than ECDSA), which can impact bandwidth, storage, and latency, particularly in resource-constrained environments like IoT or consumer electronics.

• Hybrid Approaches: To ensure security during the transition, a hybrid model is recommended. This combines classical algorithms (for tested reliability) with PQC algorithms (for future-proofing), ensuring data remains secure even if one method is compromised.

• Inventory Management: Organisations are urged to create a Cryptographic Bill of Materials (CBOM) to identify and manage vulnerable cryptographic assets within their infrastructure