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ATH Protocol Specification v0.1

This document defines the ATH (Agent Trust Handshake) protocol specification. ATH is a lightweight, decentralized application-layer security protocol that establishes trusted connections between AI agents and external services.

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Status

Version: 0.1 (Current) This is the initial release of the ATH specification, covering:
  • Agent identity model (URI-based Agent_ID + signed JWT attestation)
  • Three discovery modes (manual, gateway catalog, service-side .well-known)
  • Trusted handshake flow (Phase A: agent registration, Phase B: user OAuth consent)
  • Scope intersection enforcement
  • API endpoints (register, authorize, token, proxy, revoke)
  • Security considerations
  • Three adoption levels (gateway → agent-aware OAuth → native ATH)

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Core Principle

An agent can access a service only when both conditions are met:
AuthorizationWho decidesWhat it answers
App-sideService provider / agent registry”Is this agent allowed to use this service?”
User-sideEnd user”Does this user allow this agent to act on their behalf?”
Neither authorization alone is sufficient.

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Specification Sections

Handshake Flow

The trusted handshake protocol

Client Handshake

Client-side handshake flow

Client Reference Impl

Client reference implementation

Server Handshake

Server-side handshake flow and API endpoints

Server Reference Impl

Server reference implementation

Schema

JSON Schema reference

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Conformance

The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL” in this specification are to be interpreted as described in RFC 2119.