PATH — Protocol for Autonomous Traversal and Handshake: A Threshold-Cryptographic Overlay for Heterogeneous and Non-Terrestrial Transport

We describe an overlay construction for session-establishment traffic in which an ephemeral session key is split via a (t, n) threshold secret-sharing scheme and the resulting shares are dispatched across deliberately divergent transport paths, including at least one non-terrestrial path. The construction targets a specific, narrow class of traffic — authentication handshakes, credential exchange, session-token issuance, and command authorization — for which the ratio of per-message value to per-message size is high and conventional TLS-over-IP is known to concentrate vulnerability at the handshake. The construction extends a core cryptographic model with a proximity-mesh relay layer, a self-routing payload architecture, an Interference-Adaptive Band Orchestration (IABO) model for power-efficient multi-band dispatch, a CSS physical layer with satellite link budget analysis, indoor penetration characterization, a universal mesh architecture thesis, a return path architecture, a tiered federation operator model, and a phased commercialization roadmap. The cryptographic primitives are individually mature and well-studied. The contribution is their composition on a transport substrate — cellular, Wi-Fi, NTN satellite, and short-range mesh, all available on commodity hardware under open standards — combined with a self-routing payload model and an intelligent radio orchestration layer that together eliminate the infrastructure dependencies that make current alternatives fragile. This paper is released as a defensive publication to establish public prior art.