Determining SPHINCS+ Readiness for Standardization of SLH-DSA Signature

As quantum computing advances, public-key cryptographic algorithms risk becoming obsolete, requiring the development and implementation of quantum-resistant alternatives. This thesis evaluates SPHINCS+, a stateless hash-based digital signature scheme recently standardized by NIST under the FIPS 205 standard named Stateless Hash-Based Digital Signature Algorithm (SLH-DSA), which was selected for being a conservative and robust choice due to its reliance solely on well-understood cryptographic primitives. In the context of the growing need for quantum-resistant cryptographic solutions, determining the readiness of SPHINCS+ involves assessing its practical viability across different application domains and evaluating how well it meets today’s and future needs. To achieve this, we analyze SPHINCS+ in the following areas. Our analysis begins by benchmarking SPHINCS+ against classical and post-quantum signature schemes such as the Elliptic Curve Digital Signature Algorithm (ECDSA) and ML-DSA, measuring key generation, signing, and verification times, as well as signature sizes across multiple variants. The scheme’s performance is evaluated in constrained environments such as Vehicle-to-Vehicle (V2V) communication, simulating its integration into mock blockchain transactions and TLS-like protocols to assess feasibility and scalability. In addition, this work investigates hybrid cryptographic models that combine SPHINCS+ with classical schemes to ensure backward compatibility and cryptographic agility, as a transitional solution during this post-quantum migration period. The findings suggest that, while SPHINCS+ offers strong security against quantum computers and has been standardized by NIST, its substantial performance drawbacks raise critical concerns about its practicality. These limitations indicate that SPHINCS+, despite its conservative design, may not be suitable for many real-world applications. As such, we believe it is imperative that an alternative signature scheme be developed and standardized alongside the current selection to ensure feasibility across all types of applications.