Agent Identity Protocol (AIP): Verifiable Delegation for AI Agent Systems

This document specifies the Agent Identity Protocol (AIP), a protocol for verifiable, delegable identity for AI agent systems. AIP introduces Invocation-Bound Capability Tokens (IBCTs) that bind identity, authorization, scope constraints, and provenance into a single cryptographic artifact. Two token modes are defined: a compact mode using JSON Web Tokens (JWT) with Ed25519 signatures for single-hop interactions, and a chained mode using Biscuit tokens with append-only blocks and Datalog policy evaluation for multi-hop delegation chains. Protocol bindings are specified for the Model Context Protocol (MCP), Agent-to-Agent Protocol (A2A), and generic HTTP APIs. The protocol addresses authentication gaps in current AI agent infrastructure where a survey of approximately 2,000 MCP servers found all lacked authentication.