Paper 2024/024 Original: eprint.iacr.org/2024/024 ↗

FlexHi: A Flexible Hierarchical Threshold Signature Scheme

Abstract

Threshold signature schemes have gained prominence in enhancing the security and flexibility of digital signatures, allowing a group of participants to collaboratively create signatures while maintaining a predefined threshold of participants for validity. However, conventional threshold signatures treat all participants equally, lacking the capability to accommodate hierarchical structures often seen in real-world applications. Hierarchical Threshold Signature Schemes (HTSS) naturally extend the concept of simple threshold signatures, offering a solution that aligns with hierarchical organizational structures. Our paper introduces a novel, efficient, and flexible HTSS that employs independent polynomials at each hierarchical level, removing limitations on threshold values. This adaptability enables us to tailor the scheme to diverse requirements, whether signing requires only top-level nodes or lower-level participants' involvement. Based on our analysis, our FlexHi integrated into the FROST scheme outperforms Tassa's hierarchical scheme on FROST and operates approximately 30% to 40% faster, depending on the number of participants and the chosen threshold values. This demonstrates that, in addition to flexibility, our scheme has practical benefits through improved performance.