We Sent a Cryptographically-Signed AI Agent Payment Over 868 MHz Radio. No Internet. No Cloud. Just Trust. By Raza Sharif, CEO/Founder | contact@agentsign.dev Airplane mode. Two Heltec LoRa boards. A signed MCPS frame crossed 868 MHz radio and settled in under 2 seconds. No internet. No Lightning node. No cloud infrastructure. No blockchain. Just a cryptographic signature, a nonce, and a trust level — travelling at the speed of radio. This is what happened, how we built it, and why it matters for every AI agent you are shipping right now. The Problem Nobody Is Talking About MCP (Model Context Protocol) has 97 million SDK downloads . Over 13,000 servers are publicly listed. It is the fastest-growing AI integration standard in history. It shipped with no message signing. Not "limited signing." Not "optional signing." Zero. Any process on the network can forge a tool call. Any captured frame can be replayed indefinitely. A server has no cryptographic way to verify the agent calling it is who it claims to be.…