Empirical Evaluation of Large Language Models for Migration of Code Fragments to Post-Quantum Cryptography

Computer Science > Cryptography and Security [Submitted on 5 Jun 2026] Empirical Evaluation of Large Language Models for Migration of Code Fragments to Post-Quantum Cryptography Javier Pallarés de Bonrostro, Ana I. González-Tablas, María Isabel González Vasco The transition to post-quantum cryptography (PQC) requires not only replacing vulnerable cryptographic primitives, but also refactoring the surrounding software logic. While existing PQC migration frameworks provide organizational guidance, practical code-level remediation remains largely manual and error-prone. This paper evaluates whether large language models (LLMs) can be trained to assist in the migration of pre-quantum cryptographic code fragments to post-quantum counterparts while preserving functional correctness. To this end, we introduce a reproducible experimental framework built around a synthetic dataset of 800 paired Python code fragments covering six cryptographic families and combined multi-primitive cases. Each pair is validated through category-specific functional tests, enabling both dataset quality control and objective evaluation of model-generated migrations. Four models are assessed: GPT-4.1 in a zero-shot setting, and fine-tuned versions of GPT-3.5-turbo, GPT-4.1-mini, and CodeLlama-7B-Instruct. The results show that domain-specific fine-tuning is essential for reliable cryptographic migration. The fine-tuned GPT-4.1-mini model achieves the best overall performance, with a mean static similarity of 0.9072 and a dynamic functional correctness rate of 92.5%, substantially outperforming the zero-shot baseline. A complementary validation on six open-source repositories further shows that the approach can produce useful migrations in localized cryptographic modules, while also revealing limitations in larger projects with complex dependencies and cross-module interactions. These findings suggest that fine-tuned LLMs can serve as practical components in future crypto-agile migration pipelines, provided they are coupled with automated verification and dependency-aware validation. Subjects: Cryptography and Security (cs.CR) Cite as: arXiv:2606.07341 [cs.CR]   (or arXiv:2606.07341v1 [cs.CR] for this version)   https://doi.org/10.48550/arXiv.2606.07341 Focus to learn more Submission history From: Ana I. González-Tablas [view email] [v1] Fri, 5 Jun 2026 14:53:00 UTC (19,382 KB) Access Paper: HTML (experimental) view license Current browse context: cs.CR < prev   |   next > new | recent | 2026-06 Change to browse by: cs References & Citations NASA ADS Google Scholar Semantic Scholar Export BibTeX Citation Bookmark Bibliographic Tools Bibliographic and Citation Tools Bibliographic Explorer Toggle Bibliographic Explorer (What is the Explorer?) Connected Papers Toggle Connected Papers (What is Connected Papers?) Litmaps Toggle Litmaps (What is Litmaps?) scite.ai Toggle scite Smart Citations (What are Smart Citations?) Code, Data, Media Demos Related Papers About arXivLabs Which authors of this paper are endorsers? | Disable MathJax (What is MathJax?)