Scalability Bottlenecks in Quantum-Resilient Distributed Ledgers: A Comparative Analysis of Post-Quantum Blockchain Implementations
Distributed ledger technologies (DLTs) form critical infrastructure for decentralized applications, yet their security relies heavily on classical asymmetric cryptographic primitives that are vulnerable to quantum attacks. Post-quantum cryptography (PQC) provides candidate algorithms designed to resist such threats, but integrating these schemes into operational blockchain systems introduces significant architectural and performance trade-offs. This paper presents a comparative review of five blockchain implementations that incorporate PQC mechanisms across multiple platforms, including Hyperledger Fabric, Ethereum, and LACChain. We classify these systems using an architectural taxonomy based on the layer at which PQC is integrated, including identity-layer, key-generation, and consensus-layer modifications. To enable cross-study comparison, we apply relative delta normalization (Δ) to isolate the performance overhead introduced by PQC from differences in experimental environments. Our analysis shows that straightforward replacement of classical signatures at the identity layer can substantially increase certificate sizes by up to 925% in some implementations leading to measurable reductions in throughput and increases in transaction latency. In contrast, approaches that redesign consensus mechanisms using techniques such as identity-based encryption and aggregate signatures can mitigate these costs and, in some cases, improve throughput relative to classical baselines. These findings highlight key trade-offs between cryptographic security levels and system performance, providing practical insights for the design of scalable quantum-resistant blockchain systems.