The rapid proliferation of autonomous AI agents is driving a shift toward Machine-to-Machine (M2M) commerce, where software agents are expected to autonomously invoke and pay for Web 2.0 services. While Web 3.0 payments offer a programmable foundation for such interactions, the recently proposed x402 standard fails to enforce end-to-end atomicity across service execution, payment, and result delivery. In this paper, we present A402, a trust-minimized payment architecture that securely binds Web 3.0 payments to Web 2.0 services. A402 introduces Atomic Service Channels (ASCs), a new channel protocol that integrates service execution into payment channels, enabling real-time, high-frequency micropayments for M2M commerce. Within each ASC, A402 employs an atomic exchange protocol based on TEE-assisted adaptor signatures, ensuring that payments are finalized if and only if the requested service is correctly executed and the corresponding result is delivered. To further ensure privacy, A402 incorporates a TEE-based Liquidity Vault that privately manages the lifecycle of ASCs and aggregates their settlements into a single on-chain transaction, revealing only aggregated balances. We implement A402 and evaluate it against x402 with integrations on both Bitcoin and Ethereum. Our results show that A402 delivers orders-of-magnitude performance and on-chain cost improvements over x402 while providing trust-minimized security guarantees.

翻译：自主AI代理的快速普及正在推动机器对机器（M2M）商务的发展，其中软件代理被期望能自主调用Web 2.0服务并为其支付费用。虽然Web 3.0支付为此类交互提供了可编程基础，但最近提出的x402标准未能强制执行服务执行、支付和结果交付之间的端到端原子性。本文提出A402，一种信任最小化的支付架构，可将Web 3.0支付安全地绑定到Web 2.0服务。A402引入了原子服务通道（ASC），这是一种将服务执行集成到支付通道中的新型通道协议，能够为M2M商务实现实时、高频的微支付。在每个ASC内部，A402采用一种基于TEE辅助适配器签名的原子交换协议，确保当且仅当请求的服务被正确执行且相应结果被交付时，支付才最终完成。为了进一步确保隐私，A402集成了一个基于TEE的流动性保险库，该保险库私有地管理ASC的生命周期，并将其结算聚合为单笔链上交易，仅公开聚合后的余额。我们实现了A402，并在比特币和以太坊上集成了x402进行对比评估。结果表明，与x402相比，A402在提供信任最小化安全保证的同时，实现了数量级的性能和链上成本改进。