SpexPay: A Privacy-Preserving Pay-As-You-Go System for Dynamic Spectrum Sharing
Cryptography and Security
Summary
The authors present SpexPay, a system designed to allow wireless spectrum users to pay for usage without revealing their identities. Unlike existing centralized systems that pose privacy and accountability problems, SpexPay uses advanced cryptography and blockchain smart contracts to ensure payments are fair, private, and auditable. They built and tested a prototype showing it works quickly and cheaply, even on small devices like a Raspberry Pi. This system aims to support the future of more open and large-scale spectrum sharing markets.
Authors
Mohaimin Al Barat, Hexuan Yu, Shaoyu Li, Yang Xiao, Yi Shi, Eric W. Burger, Y. Thomas Hou, Wenjing Lou
Abstract
Dynamic Spectrum Sharing (DSS) is a cornerstone of next-generation wireless systems, yet existing solutions such as Spectrum Access Systems (SAS) rely on centralized administrators that expose sensitive operational metadata and lack cryptographic transaction accountability. Though SAS administrators, such as Google, have introduced pay-as-you-go pricing models, these approaches still face significant privacy and accountability challenges as DSS evolves toward a more open and large-scale spectrum marketplace. We present SpexPay, a privacy-preserving and auditable pay-as-you-go spectrum usage framework that enforces fine-grained, usage-linked payments without revealing user identities. Spexpay integrates BBS+ verifiable credentials, unlinkable session pseudonyms, and selective-disclosure proofs to enforce privacy-preserving access authorization, while leveraging Solidity-based smart contracts to realize automated and non-repudiable escrow settlement. By recording only pseudonymous usage evidence and hash-chained metering data on-chain, the system achieves strong unlinkability while preserving verifiable accountability and auditability. A full prototype demonstrates low end-to-end latency ($\approx$150 ms) and modest on-chain cost ($\approx$603K gas or $\approx$\$0.9), showing that SpexPay is practical for real-world DSS deployments. We also evaluated the user-side cryptographic operations on a Raspberry Pi 5 to assess scalability and suitability for edge-class hardware. Our code and artifacts are publicly available at https://github.com/iambarat/SpexPay.