인천대학교 인디고클랫폼 인천대학교 기술지원허브

Autonomous AI agents are increasingly discovering and purchasing digital services on behalf of their owners, making secure agent-to-agent payments an essential capability. Although the x402 protocol standardizes machine-to-machine payment negotiation, it does not provide decentralized agent authentication, policy-compliant autonomous payment, or atomic coupling between payment and service delivery. Because AI agents are often ephemeral, their identities disappear once execution terminates, making long-term accountability difficult to establish. This paper presents an authenticated, atomic, and policy-aware transaction protocol that extends x402 by integrating decentralized identity, account abstraction, and adaptor signatures. Mutual authentication based on decentralized identifiers (DIDs) and verifiable credentials (VCs) enables ephemeral agents to inherit delegated identities from persistent owners while maintaining a verifiable link to those owners. ERC-4337 smart accounts enforce owner-defined spending policies, preventing agents from exceeding their delegated authority. ECDSA adaptor signatures cryptographically couple payment authorization with service delivery, so that completing the payment authorization necessarily enables recovery of the key required to decrypt the service result, without relying on a trusted intermediary. We implement the proposed protocol on Ethereum Layer 1 and Arbitrum Layer 2 testnets and evaluate the gas consumption of smart-account setup and payment settlement, together with end-to-end service latency. The results demonstrate that the proposed protocol incurs only limited overhead and remains compatible with existing x402 and ERC-4337 infrastructures. These properties make it practical for trustworthy commerce among autonomous AI agents.