Imara Labs This document specifies the Secure Agent Delegation Protocol (SADP), an experimental end-to-end encrypted communication layer for user-to- agent and agent-to-agent workflows. SADP defines task capsules: signed, encrypted, individually routable protocol objects that carry agent tasks, tool invocations, and results across untrusted brokers, queues, and orchestration infrastructure. SADP provides asynchronous session establishment using signed prekey bundles, per-message forward secrecy and post-compromise recovery through a Double- Ratchet-style message ratchet, an optional hybrid post-quantum key- agreement profile based on ML-KEM-768, and an authenticated opaque- broker profile with replay protection. SADP is transport agnostic and is designed to be carried over HTTP, message queues, and existing agent protocols such as A2A and MCP without requiring those systems to be trusted with plaintext task content. Capability-based delegation semantics and scoped context disclosure are specified in a companion document.