Paper 2025/569 Original: eprint.iacr.org/2025/569 ↗

Solving Data Availability Limitations in Client-Side Validation with UTxO Binding

Abstract

Issuing tokens on Bitcoin remains a highly sought-after goal, driven by its market dominance and robust security. However, Bitcoin's limited on-chain storage and functionality pose significant challenges. Among the various approaches to token issuance on Bitcoin, client-side validation (CSV) has emerged as a prominent solution. CSV delegates data storage and functionalities beyond Bitcoin’s native capabilities to off-chain clients, while leveraging the blockchain to validate tokens and prevent double-spending. Nevertheless, these protocols require participants to maintain token ownership and transactional data, rendering them vulnerable to data loss and malicious data withholding. In this paper, we propose UTxO binding, a novel framework that achieves both robust data availability and enhanced functionality compared to existing CSV designs. This approach securely binds a Bitcoin UTxO, which prevents double-spending, to a UTxO on an auxiliary blockchain, providing data storage and programmability. We formally prove its security and implement our design using Nervos CKB as the auxiliary blockchain.